| T O P I C R E V I E W |
| Ampzilla |
Posted - 2011/04/08 : 23:35:17
Manual om H.Wolcott och hans konstruktioner .
Och intresset finns på andra sidan atlanten för dessa konstruktioner.
Så kommer Jag att visa hans lösningar från JBL PL-100( 1960) till föregångarn för hans Presence förstärkare(1975) i en serie artiklar .
Introduction:
Amplifier designs and information that is not readily available in cumulative
form elsewhere.
This is information collected under a long period because of the difficulties to
get the information from H.Wolcott.
He is/was a man who kept his secrets and did not put in all components in the schematics.
Henry Wolcott left some components out in the schematic drawings so they where not complete.
The reality and the schematics differ a little bit.
It was a common procedure for many manufactures.
This did it more difficult to copy a amplifier design correct without buying
one.
to be continued:
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| 25 L A T E S T R E P L I E S (Newest First) |
| Bubbel |
Posted - 2011/06/20 : 09:52:55
quote:
Denna artikel är nog inte slut för mig. Får läsa fler gånger för att denna mängd med information skall sjunka in. Gott jobbat.
Kan bara hålla med.
Anders |
| Bardis |
Posted - 2011/06/20 : 05:44:49
Denna artickel är nog inte slut för mig. Får läsa fler gånger för att denna mängd med information skall sjunka in. Gott jobbat. |
| Ampzilla |
Posted - 2011/06/19 : 21:41:29
AVSLUTAS HÄR:
Här kommer det sista för dom som håller på med rör
--------------------------------------------------------------
Då jag nu avslutar detta ämne.
Så vill jag bara förhands tipsa om att det kommer att bli en del instrument till salu inom snar framtid
bla en Avo VCM163
+ en massa rör ca 2000st
En transistor testare BK530
Förstärkare rör och transistor
+ en massa annat
(Lista finns för dom som är intresserade) |
| Ampzilla |
Posted - 2011/06/02 : 15:30:43
Jag hoppas det har varit intressant läsning.
Det var det mesta jag fått tag på om dessa förstärkare
Det som finns kvar är patentbeskrivningarna på hans högtalare "OMNISPHERE SPEAKER SYSTEM"
---------------------------------------------------------------
Nu om ni orkar så kommer lite Bonus Material .
+Lite annat som använts inom Försvaret .
Jag börjar med denna förstärkare
HOLT Ava1962
Jag missade när dom gick i skrotlådan.
Poweramplifier:
This section is a high feedback, linear designed to operate with low distortion at the specified loads, frequencies and voltages.
It consist of a triode preamplifier,V3B, followed by a grounded grid phase inverter,V4.
V5 is a push pull amplifier stage with plate positive feedback supplied from the output stage. V6 is push-pull cathode follower driver stage, followed by the output stage which is composed of four 5881#8217;s,V7,V8,V9 and V10, operating in push-pull parallel.
The output stage is operated in class AB-1 with current flowing in each half during approximately 300 degrees of the cycle.
The output transformer, T3 primary is divided into matched plate and cathode windings so that the stage is DC self-balancing.
The output transformer secondary is composed of two windings. One winding supplies a voltage which is fed back degeneratively to the cathode of the first stage preamplifier.
The negative feedback in this loop is approximately 22dB. The other winding is tapped to provide the output voltage.
Power Supply:
The power supply voltages ar derived from the plate and filament transformers.
Filament transformer ,T2, has tree 6.3 volt output windings.
Two windings supply power to 5881#8217;s in the amplifier output stage, and the other winding supplies all other filament requires. Both the positive and negative DC supplies are driven from the plate transformer T1.
The positive DC supply is composed of a full wave rectifier and capacitor, input pi network filter which provides approximately +420volts to the amplifier output stage and the two push-pull stages, and to the two positive DC supply voltage regulators.
The +250 volt regulator is a shunt regulator stage, V1, which supplies the plate potential for the amplifier phase inverter stage.
The +40 volt regulator is also a shunt regulator stage, V3A, which provides a very low ripple plate voltage for the first stage preamplifier.
The negative DC supply is a half wave rectifier with an RC filter which supplies #180;250 volt for bias potential in the amplifier cathode follower and output stage. This supply also energizes a #180;105 volt regulator stage,V2 , which provides a stable reference voltage for the +250 and + 140 volt regulators.
http://www.pdf-archive.com/2011/06/02/wiringcolours/wiringcolours.pdf
http://www.burwenaudio.com/Dicks_Tidbits.html
Se Krohnhite UF-101
|
| Ampzilla |
Posted - 2011/05/19 : 18:30:22
(i) sixth means to connect said sixth vacuum tube to said plate bad impedance of said fourth vacuum 25 tube to increase the effective value of said plate bad impedance, and
(j) a connection to each of the cathodes of said fifth and sixth vacuum tubes to provide oppositely phased outputs from said amplifier. 30
14. The amplifier of claim 13 comprising additionally; (a) a power amplifier connected to said fifth and sixth vacuum tubes and having an output transformer with a tertiary winding, and
(b) an impedance connected from said tertiary winding to the input of a said input vacuum tube for providing negative feedback for said amplifier.
15. The amplifler of claim 14 comprising additionally; (a) a fifth impedance connected from the cathode of said fifth vacuum tube to the grid of said fourth vac- 40 uum tube, and
(b) a sixth impedance connected from the cathode of said sixth vacuum tube to the grid of said third vacuum tube,
(c) the elements and connections of (a) and (b) of this claim providing symmetrical internal positive feedback for said amplifier.
16. The amplifier of claim 13 comprising additionally; (a) a power amplifier connected to said aniplifier and having an output transformer with a primary 50 and only a grounded secondary winding, and
(b) an impedance connected from said secondary wind- ing to the grid of said fourth vacuum tube to provide negative feedback for said amplifier.
17. A driver amplifler circuit comprising;
(a) first and second input vacuum tubes each having a grid and a cathode,
(b) first and second transistors each having a base and an emitter,
(c) lirst rneans to connect the cathode of said first input vacuurn tube to the base of said first transitor
and through a first impedance to the emitter of said first transistor to form of said first transistor a cathode impedance for said first input vacuum tube,
(d) second :means to connect the cathode of said second input vacuum tube to the base of said second transistor and through a second impedance to the emitter of said second transistor to form of said see- ond transistor a cathode impedance for said second input vacuum tuhe,
(e) third and fourth vacuum tubes, each having a grid, a cathode, a plate, and also a plate bad impedance connected to said plate,
(f) a third impedance connecting the emitter of said first transistor to the cathode of said third vacuum tube and also to the grid of said fourth vacuum tube,
(g) a fourth impedance connecting the emitter of said second transistor to the cathode of said fourth vacuum tube and also to the grid of said third vacuum tube,
(h) fifth and sixth vacuum tubes, each having a grid, a cathode and a screen grid,
(i) means to connect the grid of said flfth vacuum tube to the plate of said third vacuum tube and equivabent ineans to connect the grid of said sixth vacuum tube to the plate of said fourth vacuum tube,
(j) a fifth impedance connected between the screen grid of said flfth vacuum tube and that end of said plate load impedance opposite to the plate connection thereto of said third vacuum tube to increase the effective value of said plate bad impedance,
(k) a sixth impedance connected between the screen grid of said sixth vacuum tube and that end of said pbate bad impedance opposite to the pbate connection thereto of said fourth vacuum tube to increase the effective value of said plate load impedance,
(1) furst constant-voltage means connected between the screen grid and the cathode of said fifth vacuum tube,
(m) second constant-voltage means connected between the screen grid and the cathode of said sixth vacuum tube,
(n) a seventh impedance connected to the cathode of said fifth vacuum tube to provide a vobtage output therefrom, nnd
(o) an eighth impedance connected to the cathode of said sixth vacuum tube to provide a voltage output therefrom.
References Cited
UNITED STATES PATENTS
2,705,265
2,879,410
2,896,171
3,173,098
3,199,041
3,328711
|
| Ampzilla |
Posted - 2011/05/19 : 18:24:53
(f) the elements of (d) and (e) operative to provide an approximately infinite value of plate load
impedance to said vacuum tube for approximately distortionless amplification by said vacuum tube with a gain determined essentially by the amplification factor of the structure of said vacuum tube.
2. The amplifier of claim 1 in which said unity-gain amplifier comprises a cathode-follower vacuum tube.
3. The amplifier of claim 1 in which said unity-gain amplifier comprises an NPN emitter-follower transistor.
4. The amplifier of claim 1 in which said unity-gain amplifier comprises a PNP transistor having an emitter connected to said output terminal.
5. The amplifier of claim 1 in which said signal-pass ing means comprises a battery.
6. The amplifier of claim 1 in which said signal-passing means comprises a zener diode.
7. The amplifler of claim 6 in which said zener diode is shunted by a capacitor.
8. The amplifier of claim 1 in which said unity-gain amplifier is a cathode-follower vacuum tube having at least two grids.
9. An amplifier effective to direct current in which the amplification of the signal is determined by the amplification factor of a vacuum tube comprising;
(a) a first cathode-follower vaccum tube having a cathode and a flrst source of signal connected to said
vacuum tube,
(b) a second vaccum tube having only a grid, a cathode and a plate and having the said amplification factor,
(c) the cathode of said first cathode-follower vacuum tube connected to the cathode of said second vacuum tube and the cathodes of both said first and second vacuum tubes connected to a common impedance and therethrough to a signal ground,
(d) a second source of signal connected to the grid of said second vacuum tube and having a signal
differentially related to the signal of said first source of signal,
(e) a plate load impedance connected to the plate of said second vacuum tube,
(f) a third cathode-follower vacuum tube having at least grid, cathode and plate electrodes,
(g) said grid electrode connected to the plate of said second vacuum tube,
(h) an isolating impedance connecting said plate bad impedance to a source of energizing potential for the plate of said second vacuum tube,
(i) signal-passing means connecting said cathode electrode of said third cathode-follower vacuum tube to the junction between said plate load impedance and said isolating impedance,
(j) the plate electrode of said third cathode-follower vacuum tube connected to said source of energizing potential, and
(k) an impedance connecting said cathode electrode of said third cathode-follower vacuum tube to a signal ground, across which impedance the output signal of said amplifier appears.
10. The amplifier of claim 9 in which said signal-passing means is a capacitor.
11. The amplifier of claim 9 in which said signalpassing means is a zener diode.
12. The amplifler of claim 9 in which said signalpassing means is a battery.
13. An amplifler comprising;
(a) first and second cathode-follower input vacuum tubes,
(b) first and second emitter-follower transistors,
(c) first means to connect said first transistor as a
cathode impedance for said first vacuum tube and s
second means to connect said second transistor as a
cathode impedance for sak! second vacuum tube,
(d) third and fourth vacuum tubes, each having a grid, a cathode, a plate and a plate bad impedance,
(e) third means inciuding a first impedance to con- 10 nect said first emitter-follower transistor to the cathode of said third vacuum tube and also to the grid of said fourth vacuum tube,
(f) fourth means inciuding a second impedance to connect said second emitter-follower transistor to the cathode of said fourth vacuum tuhe and also to the grid of said third vacuum tube,
(g) fifth and sixth vacuum tubes each cathode-follower connected,
(h) fifth means to connect said fifth vacuum tube to 20 said plate bad impedance of said third vacuum tube to increase the effective value of said plate bad impedance, |
| Ampzilla |
Posted - 2011/05/19 : 18:23:31
In Fig. 6, cathode 95 of triode 90 connects to cathode resistor 85. Plate 96 thereof connects directly to grid 97 of tetrode 94. Plate 96 also connects to plate load impedance resistor 98 and therethrough to isolating resistor 99 and to positive voltage source terminal 100. This may supply a voltage of the order of 450 volts. Plate 101 of the tetrode connects directly to terminal 100, while the screen grid 102 connects to resistor 103, of 60,000 ohms resistance, and therethrough to terminal 100.
As explained in connection with Fig. 5, capacitor 104, of 60 mfd. capacitance, conveys the signal being amplified back to the junetion of resistors 98 and 99. Zener diode 105 stabilizes the potential of screen grid 102 and may have a voltage drop rating of 82 volts. A capacitor 113, of 5 mfd. capacitance, is shunted across the zener diode to insure conveyance of the signal and to eliminate diode-originated electrical noise. Cathode resistor 106 is connected to cathode 107 of tetrode 94 and may have a resistance of 20,000 ohms.
The signal that has been amplified in the recited driver stages acoording to my invention is conveyed to grid 108 of power tube 109 via capacitor 110, of 2 mfd. capacitance and via suppressor resistor 111, which may have a resistance of 100 ohms. Grid 108 is retumned to a grid bias supply #8212;C, of 30 volts negative with respect to ground via resistor 112. This resistor is typically of 100,000 ohms resistance. Cathode 114 connects to ground. Plate 115 conneets to one extremity of primary 116 of output transformer 117. The center tap of primary 116 connects to the positive terminal 118 of a power supply source of typically 450 volts. A useful load, such as a loudspeaker, is attached to secondary 119 of the stepdown output transformer.
It will be recalled that my pre-amplifiers perform excellently without feedback. However, when a power amplifier is added, a tertiary winding 120 is provided upon output transformer 117, wound with equal coupling to both sides of primary 116. The negative feedback circuit of which it is a part may be asymmetrical, one terminal of winding 120 is thus grounded. The opposite terminal connects to resistor 121, which has a resistance in the sub-megohm range, and which connects to input terminal 70. This provides over-all negative feedback. Such feedback may also be taken from secondary 119, as an alternate embodiment.
The circuit of Fig. 6 allows internal symmetrical positive feedback when the negative feedback is employed. With the symmetrical arrangement half the feedback required is provided on each side of the amplifier. Power supply variations thus become common mode variations and are less effective in introducing ripple into the signal. Such positive feedback is provided by capacitor 123, of 0.22 mfd. capacitance, connected to cathode 107 and to resistor 124, of 200,000 ohms resistance, in ,a series relation connected back to summing impedance 84, on the side that connects to grid 86 of tube 87. Resistor 124 may be made variable to realize the optimum degree of positive feedback.
Since there is no change of phase from terminal 70 to the above-defined terminal of summing impedance 84, the over-all feedback resistor 121 can be connected to that defined terminal as an alternate embodiment.
For the alternate embodiment in which secondary 119 takes the place of tertiary 120 the connections to secondary 119 are as to tertiary 120, but the secondary retains its step-down ratio as before.
It is aditionally possible to provide further negative feedback, and of a balanced nature, by connecting capacitor 122, which may have a small capacitance of the order of from one to three mmfd., from plate 115 to grid 86 of triode 87. A symmetrical connection is made from the lower side of the amplifier to grid 89 of triode 90. This feedback is effective at the high frequencies of the signal- handling range of the amplifier.
In order that equal gain be provided for signals applied to both cathode 95 of triode 90 and grid 86 of triode 87, a voltage divider comprised of resistors 85 and 93 is formed to give additional loss in the cathode circuit. The gain of triode 90 (and triode 87 as well) is µ for a signal impressed upon the grid and it is µ + 1 for a signal impressed upon the cathode. The loss is adjusted to make the gain equal to in each case.
It will be noted that input signal e1 is provided as an amplified output from the driver stages at capacitor 110 as a non-phase-inverted signal, while input signal e2 is inverted at that capacitor. The opposite state of affairs holds at corresponding output capacitor 125.
Although specific examples of voltages and values for circuit elements have been given in this specification to illustrate the invention, it is to be understood that these are by way of example only and that consonant departures can be taken therefrom without departing from the inventive concept. Other modifications of the circuit elements, details of circuit connections and alteration of the coactive relation between elements may also be taken under my invention.
Having thus fully described my invention and the man ner in which it is to be practiced, I claim:
1. An amplifier effective to zero frequency comprising;
(a) a vacuum tube having only a grid, a cathode and a plate,
(b) a load impedance connected to said plate,
(c) an other impedance connected to said load impedance and also in series to a positive voltage source,
(d) a non-phase-inverting essentially unity-gain amplifier connected to said plate and to an output terminal,
(e) constant voltage signal-passing means having an impedance low with respeet to that of said load im-
pedance connected from said output terminal to the junction between said load impedance and said other impedance,
to be cont. |
| Ampzilla |
Posted - 2011/05/19 : 18:21:45
Additionally, the cfrcuit of Fig. 5 provides for accepting a differential input signal; this being e1 at input terminal 41 and e2 at input terminal 42. These input terminals are returned to ground via resistors 43 and 44, respectively, each having a resistance of the order of 1 megohm. Each input terminal is connected to the grid of an input vacuum tube; as grid 45 of tube 47 and grid 46 of tube 48, respectively. These tubes may be the two sections of a type 12AX7 vacuum tube. Both cathodes, 49 and 50, are connected together and to a common cathode resistor 51, which has a resistance of 50,000 ohms for a typical example in which the total cathode current is 2 milliamperes. This resistor is in turn connected to the negative terminal of C-battery 52, the positive terminal of which is connected to ground. Typically, this battery has a voltage of 100 volts.
Plate 53 of triode 47 is connected directly to a tap on plate supply battery 54. The whole voltage of this battery is of the order of 400 volts, with the tap being at 150 volts. Both batteries 52 and 54 may be replaced by regulated power supplies, as is known to the art. Triode 47 is connected to be a cathode-follower vacuum tube.
The other triode, 48, becomes the one having the effective infinite plate load impedance, as will be generally recognized from the circuit thereof in relation to the circuits previously described. The plate 56 thereof connects to resistors 57 and 58 in series, which, in turn, are connected to the positive terminal of battery 54. Tetrode 59 (which may also be a pentode) serves in the place of triode 15 of Fig. 2; the possibility of which was previously mentioned. Grid 60 connects directly to plate 56 of triode 48 of Fig. 5. Plate 61 of tetrode 59 connects directly to the positive terminal of battery 54. Screen grid 62 also connects to the positive terminal of battery 54, but through resistor 63. The value of this resistance must be low enough to supply both the screen current and the current to operate zener diode 64, the latter operating to provide a fixed voltage for the screen grid with respect to the potential of cathode 65. The anode of the zener diode is connected to cathode 65. The zener diode may have a constant voltage drop rating within the range of from 30 to 100 volts, depending upon the screen voltage required for the particular type of tube employed for tube 59.
Cathode 65 is also connected to ground through cathode resistor 66, typically having a resistance of 20,000 ohms, and further, to output terminal 67 and to capacitor 40, the latter having been previously identified. The embodiment of Fig. 5 thus provides an amplifier having a differential input and a single-ended output. Fig. 6 shows a complete amplifier, having, for example, a power output capabiity of 250 watts and a gain of the order of 100 times. A double-ended input is provided with a double-ended output from the driver stages, while a push-pull output is had from the power amplifier.
The circuit is symetrical insofar as the amplifier proper is concerned, thus, only the top half of Fig. 6 will be described in detail.
An input signal e1 (differentially related to an opposite signal e2) is impressed at input terminal 70. This connects directly to grid 71 of vacuum tube 72, which vacuum tube may be one section of a 12AX7 type. The grid is returned to ground through resistor 73, of one megohm resistance. Plate 74 is connected directly to a source of plate supply voltage, the positive terminal of which is represented by terminal 75. The voltage here may be 125 volts.
Cathode 76 is connected directly to base 77 of NPN transistor 78 and also to one terminal of resistor 79, which resistor may have a resistance of 3,000 ohms. Emitter 80 of transistor 78 connects to the second terminal of resistor 79. Collector 81 thereof connects directly to positive terminal 82, which may supply a voltage of six volts.
Emitter 80 also connects to resistor 83, of 7,000 ohms resistance, and therethrough to negative voltage source #8212;C, which typically supplies a minus 39 volts potential.
It is seen that transistor. 78 forms a cathode impedance for cathode-follower-connected triode 72 and provides a reduction in driving impedance to the following stages of over 100 times; i.e., from 1,000 ohms to less than 10 ohms.
Transistor 78 also enhances the already good linearity of operation of tube 72 by providing a high effective cathode impedance for the tube. The value of this impedance has a principal component which is equal to the resistance of resistor 79 divided by one minus the voltage gain of transistor 78. This voltage gain closely approaches unity.
This impedance value is shunted by the input impedance of the transistor, which input impedance is approximately equal to the resistance of resistor 83 times the beta value of the transistor.
Emitter 80 also connects to summing impedance 84, which is here shown as a resistor having a resistance of the order of 1,000 ohms. The second terminal of impedance 84 connects to a cathode resistor 85 and also directly to grid 86 of opposed triode 87. An equivalent circuit connects summing impedance 88 directly to grid 89 of triode 90 and to cathode resistor 91 for triode 86. Cathode resistors 85 and 91 have a nominal value of 1,000 ohms each. These are each shunted by a cathode bypass capacitor, as 92, having a capacitance of 0.01 mfd. An additional resistor 93 connects the junction of cathode 95 and resistor 85 to ground. It has a resistance of 50,000 ohms.
Vacuum tubes 90 and 94 may be the triode-tetrode combination in one vacuum envelope known as the ECL86 (European) or 6GW8 (United States). In such tubes the connection from the plate of the triode to the control grid of the tetrode is essentialby internal and a driven shield is provided, all having the effect of lowering the distributed capacitance of the tubes. This increases the bandwidth of operation to a substantial degree. If extension of the upper frequency of operation is not important, then separate vacuum tubes may be used, and, if desired, a pentode for tube 94.
to be cont. |
| Ampzilla |
Posted - 2011/05/17 : 19:36:56
The inherent stability of the gain of my amplifier is believed to represent a highly significant advance over the prior art.
In the practical embodiment of Fig. 2, elements 1 through 10 have the same characteristics, interconnection and function as previously described in connection with Fig.1. In an illustrative example, with one section of the dual 12AX7 for vacuum tube 1, the negative bias, C#8212;, may be of the order of 1#188; volts; the grid return resistor, 4, may be one megohm; plate loadad resistor, 8, may be 50,000 ohms; isolation resistor, 9, may be 75,000 ohms; and the voltage of the positive supply, 10, may be 250 volts. Instead of the C bias the known cathode bias resistor may be used and may have a value of 1,250 ohms.
In Fig. 2 amplifier 11 becomes cathode-follower-connected vacuum tube 15. This may be the second triode section of a 12AX7 vacuum tube or it even may be a pentode. In any event, the grid thereof 16 connects directly to previous plate 7. Plate 17 connects directly to positive voltage supply 10. Cathode 18 connects to cathode resistor 19, wihich resistor has a resistance not more than 60,000 ohms. The opposite connection to resistor 19 connects to ground. Cathode 18 also connects to the anode of zener diode 20, the cathode of which connects to the junction between resistors 8 and 9. The zener diode takes the place of battery 12 in Fig. 1, in that it provides a fixed voltage drop through which the alternating signal can flow. The output terminal of the single stage of amplification is 21 and this also connects to cathode 18.
The maximum output voltage swing is limited to a value less than the voltage drop across resistor 9 and increases in proportion to the ratio of the current through zener diode 20 to the durrent through vacuum tube 1.
The current through tube 15 should be at beast equal to the current through the zener diode, which, in turn, should be at least equal to the current through vacuum tube 1.
This situation limits the output voltage swing to approximately 50% of the quiescene voltage drop across resistor 9.
In Fig. 3 the same type of arnplifler stage is illustrated with an NPN transistor 23 taking the place of prior amplifier 11. Elements 1 through 10 are as has been previously described. The voltage at terminal 10 is preferably less than before because of the limitation imposed by the breakdown voltage of transistors. It is thus desirable to use a tube that will operate at lower voltages, such as a 6DJ8.
Transistor 23 is connected as an emitter-follower, with base 24 connected directby to plate 7, collector 25 directly to positive voltage source 10, and emitter 26 connected to emitter resistor 27, which is in turn connected to ground. Emitter 26 is also connected to the anode of zener diode 28 and to output terminal 29. The cathode of the zener diode connects to the junction between resistors 8 and 9. Emitter resistor has a resistance such that current requirements are met; that is, resistor 27 has a value not to exceed 25,000 ohms for the example being considered. The voltage drop required of the zener diode is in the range of 5 to 15 volts. Transistor stage 23 has a gain close to unity and the circuit functions as has been previously described.
Fig. 4 follows the circuit of Fig. 3 in elements 1 through 10. PNP transistor 31 takes the place of prior
NPN transistor 23. The base 32 of the PNP transistor connects directly to plate 7; its collector 33 connects directly to ground; and collector 34 connects to the anode of zener diode 35, the cathode of which connects directly 5 to the junction between resistors 8 and 9. The voltage drop for this zener diode is also preferably in the 5 to 15 volt range. Capacitor 36, of 5 mfd. capacitance, connects directly across the zener diode 35 and insures that the signal which flows in this circuit shall have a low impedance path. This capacitor also prevents addition of noise to the circuit, as may be caused by the operation of certain zener diodes. An equivalent capacitor may be employed across the zener diode in Figs. 2 or 3 for the same reason.
In Fig. 4, output terminal 37 connects to emitter 34 of the transistor. It will also be understood that the battery 12 of Fig. 1 may be employed in Figs. 2 through 4 instead of the zener diode and that a capacitor 36 may additionally be shunted across the battery.
In each of the circuits of Figs. 1 through 4 the effective plate loadad impedance (resistance), R#8217;, is:
RL#8217;=RL /1-A = RL /1-1(approx.) = Infinity (approx.) (3)
Each of the circuits of Figs. 1 through 4 are direct current amplifier circuits. When this capability is not required or desired the circuit of Fig. 5 may be employed. A capacitor 40, typically of 50 mfd. capacitance, takes the place of the prior battery 12 or the zener diodes. It will be understood that the circuits of Figs. 1 through 4 could also use the capacitor 40 and that a zener diode or a battery could be used in Fig. 5. The ampliflcation of the circuit of Fig. 5 is effective to zero frequency, but not at full amplitude nor at the prior long term stability below a frequency of ten cycles per second, as an example.
The amplitude may reduce to 75% of that at frequencies above .ten. cycies at zero frequency. and the stability will be in part dependent upon such parameters as make up mutual conductance and not upon the amplification factor µ alone. |
| Ampzilla |
Posted - 2011/05/17 : 19:32:44
Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawings, in which are set forth by way of illustration and example certain embodiments of my invention.
Fig. 1 is a schematic diagram of my amplifier stage with a generically indicated additional amplifying means of unity voltage gain for providing an effectively infinite plate loadad impedance,
Fig. 2 is the same with a cathode-follower vacuum tube additional amplifying means,
Fig. 3 is the same with an NPN transistor additional amplifying means,
FIG. 4 is the same with a PNP transistor additional amplifying means,
Fig. 5 is a schematic diagram of a differential signal input amplifier stage with a tetrode additional
amplifying means,
Fig. 6 is a schematic diagram of a complete differential input, push-pull output amplifier employing tetrode additional amplifying means.
In Fig. 1 numeral 1 represents a vacuum tube, of which one of the triode sections of a 12AX7 vacuum tube is an example. A signal to be amplified, e1, is impressed upon terminal 2, which connects to grid 3 of tube 1. A grid return impedance, as resistor 4, connects to a source of negative potential C#8212; and therethrough to signal ground to provide the known negative grid bias upon grid 3.
Cathode bias may also be used without the usual degeneration at low and medium audio frequency ranges since the cathode-plate current is essentialby constant with my constant current type amplifler circuit. Cathode 5 is connected to ground 6. Plate 7 is connected to a plate impedance, which is here shown as resistor 8. Isolation resistor 9 connects between plate resistor 8 and a known plate voltage power supply or battery indicated by + terminal 10. Amplifler 11 is a non-phase-inverting amplifier stage having, ideably, a gain of one.
Battery 12 connects from the output of amplifler 11 to the junction between resistive elements 8 and 9. Battery 12 determines, in combination with resistor 8, the plate current of tube 1. In this type of circuit the plate current is equal to the voltage of bat tery 12 divided by theresistance of resistor 8.
Signal variations are transmitted through battery 12 substantially without attenuation. The amplified output signal, e0, appears at the output of ampbifier 11, at terminal 13.
Amplifier .11 acts to provide an infinite plate load impedance for vacuum tube 1 by providing a signal of the same phase and of essentially the same amplitude at the junction between resistors 8 and 9 as appears at plate 7.
This makes the voltage at both points independent of current flow; a mathematical indeterminate which has the effect of an infinite plate load impedance.
When the gain of amplifier 11 is exactly unity, the multiplication of the vaiue of the actual plate load resistor 8 is infinite and so the plate load impedance is infinity.
Cathode-follower vacuum tubes or emitter-follower transistors provide realizable practical embodiments of amplifler 11. The gain of the same can approach but not reach unity. Thus, the multiplication factor is large, but not infinitely large. For example, if the gain of amplifier 11 is 0.99, the multiplication is 100 times.
A resistance of 50,000 ohms is typical for resistor 8; thus the effective plate load impedance is
50,000* 100=5 megohms. A satisfactory plate current for the typical 12AX7 vacuum tube triode section is one milliampere. The 5 megohm effective plate load impedance is sufficient to give a substantially horizontal load line and thus one which avoids the crowded relation of the plate current vs. plate voltage curves for the vacuum tube at low plate current values.
As to the stability of gain of the amplifler, consider the known equation for the gain of a vacuum tube amplifying stage:
A= µ*RL/RL+Rp (1)
where:
µ=amplification factor of the vacuum tube
RL=load impedance
Rp=internal plate impedance of the vacuum tube
In the present instance, where the plate load impedance is, for all practical purposes, infinite, the denominator term RP may be neglected.
Thus we have:
A=µ* RL/RL =µ (2)
The amplification factor µ depends onby upon the physical structure of the vacuum tube; principally upon the distance from grid to cathode and grid to plate and the fineness of the grid mesh (i.e., the closeness of spacing of one grid wire to the next within the electron stream between cathode and plate.
It is immediately evident that the gain of my amplifier is independent of the usual operating parameters; such as mutual conductance, which is the quotient of the amplification factor over the internal plate impedance. The lat ter is affected by such operating factors as plate current, plate voltage, filament (heater) voltage, emissivity of the cathode, and by residual conditions within the vacuum tube throughout its life.
to be cont. |
| Ampzilla |
Posted - 2011/05/16 : 23:12:13
Den sista förstärkaren i denna serie blir storebror till JBL:s Pl-100
som kom i ett antal olika varianter på ingångssteg och utgångstransformatorer
Amplifier 1015/PA250
INFINITE PLATE LOAD IMPEDANCE AMPLIFIER
His invention relates to an amplifier having inherently low distortion and high gain stabiity.
The family of plate current vs. plate voltage curves for equal increments of grid bias potential are wel known in the vacuuni tube art. By means of the known loadad line the linearity performance of the tube as an amplifier can be predicted. Since the plate load is invariably an impedance of finite magnitude, the load line invariably is considerably inclined to the horizontal and it extends downward into the region where the curves run together at low plate currents.
However, should the load line be horizontal, the incrernents of plate voltage change for equal increments of grid voltage are relatively in a linear relation. This is particularly true for frame grid vacuum tubes.
The horizontal load line represents operation with a plate load impedance of infinite value. Such a value can- not be actually achieved in practice, but a reasonable approach to the same, of the order of several megohms, for the equivalent plate load impedance can be achieved. This is while still retaining the operation of the vacuum tube in the usual and desired milliampere range of plate current. The degree of distortionless amplification obtained is essentially the same as for the fully infinite bad line.
I am able to approximate an infinite load impedance for a vacuum tube by adding active circuit elements to a plate load impedance of usual value.
I obtain an additional dividend by accomplishing an effectively infinite load impedance in that the gain of the amplifier becomes independent of all usual operational factors and is determined exclusively by the amplification factor of the vacuum tube. This provides excellent gain stability.
Accordingly, I obtain the characteristic of negative feedback without employing such feedback. This is important in certain applications of an amplifier where negative feedback cannot be applied. These include a resistance-capacitance tuned audio oscilator or a frequency-selective amplifier, or particularby where local positive feedback is used to increase gain. In other applications of my amplifier, where negative feedback can be applied, distortion is reduced and stability is increased by a whole order of magnitude over that possible to the prior art.
Extreme amplifier fidelity and stability is demanded in the present day electronics art. As an example, in calibrating the recently-developed digital-indicating voltmeter having a four place indication, an amplifier having an output amplitude stabiity of 0.01% is required in combination with a similarby stable signal source. Unless this is achieved the last decimal place on the voltmeter will flutter between two values. If the operator is attempting to calibrate at 20.00 volts, say, this might mean recycling of the whole register between the 19.99 and 20,000 values. Under these circumstances calibration is inconvenient.
In the matter of fidelity, spurious effects of amplifiergenerated harmonics cannot be tolerated in instrumentation applications. In the calibration of meters the presence of harmonics causes a difference between the indications of a thermal type meter and a rectifier type meter having equal sensitivities. Because of the resonant mechanical amplification of certain frequencies in practical vibration exciters the amplifiers to calibrate the same must be essentially free of harmonics. Because the #8220;Q#8221; of the mechanical resonances may be high, the vibrational amplitude at a harmonic may even be equal to the vibrational
amplitude of the desired fundamental. Such a condition obtains if the Q for the mechanical resonance was 100 and the distortion (i.e., harmonic) was 1% of the funda mental.
My additional active element used in conjunction with the plate load comprises a constant current source in the form of an additional vacuum tube or a transistor connected to the plate load.
An object of my invention is to provide a highly linear and highly stable electrical amplifier.
Another object is to provide an amplifier that employs both a vacuum tube and a transistor in a single stage.
Another object is to provide an amplifier having a gain dependent only upon a structural parameter of a vacuum tube.
Another object is to provide an amplifier having single ended or differential inputs as well as single-ended or push pull outputs.
Another object is to provide an amplifier that is relatively simple and inexpensive and which operates at nominal supply voltages.
to be cont. |
| Gubben i Kalmar |
Posted - 2011/05/16 : 08:01:28
quote:
Måndag förtsätter jag med del 3 i serien om Wolcotts förstärkare
Det låter "najs". |
| Ampzilla |
Posted - 2011/05/15 : 22:49:50
Som ni kanske förstått så har dessa förstärkare från början bara varit tillgängliga för Militären och kalibrerings-laboratorier.
Men då jag har haft den förmån att jobba med dessa produkter så har man blivit lite "bortskämd"
Uppbyggnadsmässigt så är det mesta inom denna typ av konstruktioner mer påkostade materialmässigt än standard produkter.
(Många av Dagens produkter har alldeles för mycket fel i sina chassien
förklaring kommer senare)
Måndag förtsätter jag med del 3 i serien om Wolcotts förstärkare
|
| Ampzilla |
Posted - 2011/05/14 : 00:40:18
Innan den sista presentationen av dessa förstärkare kommer så visar jag schemat på hans
Single End Push Pull amplifier
Då denna förstärkare var / är för Mil och kalibrerings lab så är det väldigt höga spänningar= INGET FÖR NYBÖRJARE att jobba med.
Men det går kanske att omvandla topologin till något vettigare och mer normalt användande.
(Om det är någon som försöker så vore det intressant att höra hur det går)
Single End SEPP amplifier
part1 PowerSupply
Part 2 input stage
Part 3
Part 4
Part 5
|
| Ampzilla |
Posted - 2011/05/08 : 23:45:38
Då det kompletta schemat hans förstärkare är lite stora att kopiera ca 2m långt och .6m brett så kommer det lite senare.
Nästa gång kommer del 3 och den sista av av hans konstruktioner + lite annat
|
| Ampzilla |
Posted - 2011/05/08 : 23:40:46
The place of constant current source 10 in Fig. 2 is taken by the tube and circuit 50 in Fig. 4. Cathode electrode 61 thereof is connected to plate 49 of main tube 41 through cathode resistor 62. Plate electrode 63 is connected to the positive terminal of voltage supply 48, which supply may have a voltage of the order of 200 volts in a representative embodiment. Grind 64 is given a positive potential by battery 65 in the same manner as was provided by voltage divider 58, 59 in the cathode constant
current source 46. However, a #8220;floating#8221; battery is required for grid 64, since one terminal of the battery must be attached to output signal terminal 51. The battery may be of the small bias cell type in order to have low stray capacitance to ground. A voltage of the order of 50 volts is typically required. As before, the voltage drop in cathode resistor 62 brings the cathode potential 1.5 to 3 volts positive with respect to the grid f or usual vacuum tubes suited for my amplifier.
The current passed by constant current source 50 is half that passed by source 46. The potential at plate 49 is of the order of +50 volts and at grid electrode 64 it is +100 volts. The current and voltage for vacuum tube 40 is balanced with respect to that of vacuum tube 41 by volt age divider 66, 67; this being connected in series between battery 48 and ground. The junction point between resistors 66 and 67 is connected to plate 47; this plate being held at approximately 50 volts (for no DC signal).
In addition to the use of my amplifier as an amplifier per se it will be understood that it may be incorporated as the amplifying part of related devices, such as bridge oscillators. It may also be made a part of multi stage power amplifiers. In any such embodiments its superior characteristics have been found to signficantly improve the overall characteristics of the whole apparatus.
Although specific examples of voltages, graphs and values for the several circuit elements have been given in this specification to illustrate the invention, it is to be understood that these are by way of example only and that reasonably wide departures can be taken there from without departing from the inventive concept. Other modifications of the circuit elements, details of circuit connections and alteration of the coactive relation between elements may be taken under my invention.
Having thus fully described my invention and the manner in which it is to be practiced, I claim:
1.A direct current amplifier in which the ampilfication of the signal is substantially completely determined by the amplification factor of each section of a dual vacuum tube comprising;
(a) a dual triode vacuum tube structure, each of the triodes having a grid, a plate, and a cathode in common,
(b) only a single constant current source connected between said common cathode and signal ground,
(c) means connected to said two grids for differentially impressing a signal to be amplified upon said grids,
(d) a second constant current source,
(e) a connection from said second constant current source to only one of said two plates and to a signal ground,
(f) a conductor solely connecting the other of said two plates to said signal ground, and
(g) means having an impedance commensurate with that of said second constant current source connected to the same one of said two plates to obtain the amplified signal.
2.
The direct current amplifier of claim 1 in which;
(a) the first said constant current source includes an
NPN transistor, and
(b) means to directly connect said NPN transistor to said common cathode; and
(c) the second said constant current source includes a PNP transistor; and
(d) means to connect said PNP transistor to said only one of said two plates.
3.
The direct current amplifier of claim 1 in which the first said constant current source includes;
(a) a transistor having emitter, base and collector electrodes
(b) means to fix the potential of said base electrode connected thereto,
(c) means to directly connect said collector electrode to said common cathode,
(d) a resistive impedance having a value to cause the first said constant current source to pass two units of current,
(e) means to connect said emitter electrode to said resistive impedance, and
(f) means to connect said resistive impedance to a signal ground.
4.The direct current amplifier of claim 1 in which the second said constant current source includes;
(a) a transistor having emitter, base and collector electrodes,
(b) means to fix the potential of said base electrode connected thereto,
(c) means to connect said collector electrode to said only one of said two plates,
(d) a resistive impedance having a value to cause the second said constant current source to pass one unit of current, said resistive impedance connected to a source of energizing potential for said one of said two plates, and
(e) means to connect said emitter electrode to said resistive impedance.
5.
The direct current amplifier of claim 1 in which the first said constant current source includes;
(a) only a third vacuum tube having third cathode, grid and plate electrodes,
(b) means to fixedly bias said third grid electrode connected thereto,
(c) means to connect said third plate electrode directly to said common cathode,
(d) a resistive impedance,
(e) means to connect said third cathode electrode only to said resistive impedance, and
(f) means to connect said resistive impedance to a signal ground having a source of negative supply voltage.
6.
The direct current amplifier of claim 1 in which the second said constant current source includes;
(a) a fourth vacuum tube having fourth cathode, grid and plate electrodes,
(b) single means to fixedly bias said fourth grid electrode directly connected thereto,
(c) a resistive impedance,
(d) means to connect said resistive impedance to said only one of said two plates and to said fourth cathode electrode, and
(e) means to connect said fourth plate electrode to a source of energizing potential for said only one of said two plates.
7.
The direct current amplifier of claim 1 in which;
(a) said dual vacuum tube structure is comprised of two separate vacuum tubes, and
(b) said common cathode is formed by directly connecting the cathodes of said two separate vacuum tubes.
References Cited
UNITED STATES PATENTS
2,762,010
2,897,429
2,941, 155
3,178,651
3,111,630
FOREIGN PATENTS
816,664 7/1959 Great Britain.
|
| Ampzilla |
Posted - 2011/05/08 : 23:39:56
This is because the plate current IP is constant, regardless of the value of the plate voltage EP. Now, the increments of plate voltage for equal increments of grid voltage are all very nearly or exactly equal. Thus, the fidelity of amplification has been very greatly improved; it approaches perfection.
With constant current source 6 in the cathode circuit of Fig. 2 it is seen that the fidelity of the first section of twin tube Ia, section 2, 4, 7, is also very nearly perfect. This section functions as a cathode follower for the signal impressed upon grid 2; i.e., signal e1. With the substantially infinite cathode impedance the known self negative feedback of a cathode follower approaches 100%, giving substantially perfect fidelity. The distortion is reduced by l/µ times the distortion present in a grounded cathode stage.
Thus, both sections of tube 1a operate with excellent fidelity.
A typical practical circuit for accomplishing the performance set forth in connection with Figs. 1 or 2 is shown in Fig. 3. By noting the reference numerals emplayed in FIGS. 1 and 2 it is seen that the single vacuum tube of Fig. 1 corresponds to the right-hand triode of tube la of Fig. 2. Similarly, in the practical circuits of Figs. 3 and 5 the right-hand tube of each corresponds to the single tube showing of Fig. 1.
In Fig. 3, the basic vacuum tube structure is shown as two separate triodes lA and 1B. These preferably have identical characteristics, but it is immaterial whether or not both are housed in one vacuum envelope. Signal e1 is introduced to grid 2 as before. Grid return resistor 13 provides a path to ground to establish a fixed grid potential around which the signal e1 may vary. Constant current source is comprised of transistor 14 and this may be of the NPN type.
A transistor constitutes a constant current device in that the collector current is relatively independent of the collector voltage. This characteristic is enhanced by adding resistance in the emitter circuit; i.e., resistor 19 in Fig. 3. A suitable resistance value for this resistor is of the order of 500 ohms.
A proper bias is placed on base 15 of transistor 14 by the voltage divider composed of resistors 16 and 17, the junction between which is connected to the base. The other terminal of resistor 16 connects to a source of supply voltage 18. The latter provides a. voltage negative with respect to ground, which voltage may be of the order of 11 volts. A fraction of this voltage is applied to base 15. Through resistor 19 the whole of the voltage of source 18 is applied to emitter 20 of transistor 14. Collector 21 thereof is connected directly to both cathodes 4 and 5 of vacuum tubes lA and 1B. In a typical embodiment the elements of transistor 21 circuit are adjusted to give a constant current of 10 milliamperes.
Additional constant current source 10 is largely embodied in transistor 21. For convenience in supplying energizing voltages this transistor is of the PNP type. Base 22 thereof is provided with a proper bias, as 70 volts positive with respect to ground, by the voltage divider comprised of resistor 23 in series with resistor 24. These resistors are connected between a source of voltage supply, represented by battery 8, and ground. The junction between the two resistors is connected to base 22.
A preferred voltage for battery 8 is 75 volts. The ratio of the resistance of resistor 24 to the resistance of resistor 23 determines the percentage of the supply voltage appearing across resistor 26. This is preferably 5 to 10 times the base to emitter drop for transistor 21, to minimize the effect of temperature upon the constancy of the constant current function. Emitter 25 is connected to the positive terminal of battery 8 through resistor 26. This resistor has a resistance value selected to provide the desired constant current flow. The resistance value is usually less than that of resistor 23. In a typical embodiment the elements of transistor 21 circuit are adjusted to give a constant current of 5 milliamperes through vacuum tube section 1B.
Vacuum tube lA is also energized from voltage source 8 through resistor 27, which has a value to cause the plate voltage of tube lA to be the same as the plate voltage of tube 1B. This arrangement consumes the total of 10 milliamperes passed by the cathode constant current source comprising transistor 14. The voltages at each of plates 7 and 9 are equal under these conditions, at a value of the order of 55 volts. Where no use is made of the signal from plate 7 a by- pass capacitor 28 is connected there from to ground.
Such a capacitor is to be in the microfarad range and it is effective in reducing power supply ripple, that is, when
battery 8 is replaced by the usual power supply in practice. If only an alternating current signal is carried by the amplifier capacitor 28 is effective in the usual bypass function, but for direct current amplification it is not effective. Similar capacitors may be placed across resistor 16 and across resistor 23 to achieve similar results.
The circuit of Fig. 5 follows the circuits of Figs. 2 and 3, but employs vacuum tubes throughout. The twin differential amplifier tubes 40 and 41 are as 1a and 1A and 1B before. Grids 42 and 43 are provided with differentially originated components of signal, as has been discussed. Grid return circuits 52 and 53 are represented by resistors connected to signal ground and may be either of this form or the equivalent in paths through coupling apparatus employed to feed the desired signals to the amplifier. Cathodes 44 and 45 are made common by a connection and this is connected to the plate electrode 54 of a constant current source generally represented by numeral 46.
Cathode 55 of the constant current source tube 46 is connected through cathode resistor 56 to a source of negative supply voltage 57, which source may have a voltage of the order of #8212;150 volts. Resistors 58 and 59, also connected in series from the negative terminal of source 57 to ground, form a voltage divider to impress a potential of the order of #8212;100 volts upon grid 60. The drop due to the constant current in this circuit causes cathode 55 to assume a potential more positive than that of grid 60 by the amount of the desired grid bias, typically 1.25 to 45 3 volts. As before, the bias on grid 60 is set to provide a constant current flow sufficient for the cathode to plate current of both tubes 40 and 41. Circuit 46 takes the place of constant current source 6 in Fig. 2. A bypass capacitor 68 may be employed across resistor 58 to reduce power supply ripple, etc., as was mentioned in connection with resistors 16 and 23 of FIG. 3. |
| Ampzilla |
Posted - 2011/05/08 : 23:38:42
Considering my amplifier analytically, the voltage amplification A of a single conventional vacuum tube stag.
A=µ*RL/RL+RP
wherein:
µ=amplification factor of vacuum Tube 1
RL#8217;=load impedance
RP=internal plate impedance of the vacuum tube
In the present instance the plate load impedance for the triode 3, 5, 9 of Fig. 1 is essentially infinite, since the current which flows in a constant current source, as 10, is independent of the voltage impressed across it. Thus, the term Rp be neglected and so we have for a signal e1 impressed upon the grid:
A=µ* RL/RL=µ
For a signal e2 impressed upon the cathode, this is
A=(µ+1)*RL/RL =µ+1
The amplification factor µ of a vacuum tube is dependent only upon its physical structure; mainly, the distance of the grid from the cathode and from the plate and the is the well known expression:
fineness of the mesh of grid wires (Ie., the closeness of spacing of one grid wire to the next, which influences the flow of the electron stream from the cathode to the plate).
It is immediately evident that I have achieved a great independence from the plural operating pararneters which heretofore have affected the gain of an amplifier. One such parameter is mutual conductance, which is the quotient of the amplification factor over the plate impedance. The plate impedance is affected by such operating factors as plate voltage, cathode heater voltage, emissivity of the cathode and by residual factors within the vacuum tube throughout its life. Thus, the performance of my amplifier is essentially independent of the life cycle of the vacuum tube, its operating voltages and certain parameters.
In Fig. 2, numeral Ia represents a pair of vacuum tubes. These may be in a single vacuum envelope, as the known dual or twin triodes, of which the 6DJ8 tube is an example. In a typical application of the invention, grids 2 and 3 are provided with differentially-related components of an input signal from a known source not shown. Cathodes 4 and 5 are connected together inside or outside of the tube and the common connection is connected to first constant current source 6. This, in turn, is connected to signal ground 30. Plate 7 is connected to a source of positive energizing potential 8. Plate 9, coactive with grid 3 and cathode 5, is connected to second constant current source 10. This, in tum, is connected to energizing potential source 8.
In numerous applications of the amplifier I prefer to introduce the signal upon one grid, as grid 2, as signal e1j, and to obtain a first input type of #8220;differential#8221; operation. This is accomplished by the provision of constant current source 6, which is characterized as the first such source for identification. In this type of operation the second input signal is zero.
Source 6 provides essentially infinite impedance in the common circuit of cathodes 4 and 5. This impedance is very large with respect to an ordinary load impedance in a plate circuit. Additionally, it is desirable and possible to select tube Ia with two sets of electrodes 2, 4, 7 and 3, 5, 9 having the same amplification factor µ. Under these conditions very good differential amplifier functioning is obtained. This contemplates the introduction of two differentially related signals, one upon grid 2, (e1), and one upon grid 3, (e1j); i.e., the usual type of differential operation. The amplifier is responsive only to the difference of the two signals and the common mode rejection is high. The latter means, of course, that any signal introduced to both grids 2 and 3 in the same phase is not amplified.
In order to note the difference between my amplifier and that of the prior art, please consider the following. In the type of differential operation treated directly above the amplification obtained at terminal 11 in Fig. 2 of a signal e1 introduced upon grid 2 would be only half that defined by Equation 1 for the nominal value of cathode impedance of the prior art. This occurs because the section of the tube 2, 4, 7 acts as a cathode follower, driving the cathode of section 3, 5, 9 as a grounded grid stage. In looking back into each cathode circuit the impedances are equal. With source and receiver impedances equal the well known loss of one-haif, or 6 db, is experienced.
With my relatively infinite impedance 6 in the common cathode circuit, section 2, 4, 7 acts as a cathode follower with a near infinite impedance load and thus provides an amplification that is very nearly equal to:
A#8217;=µ/µ+1 (4)
This is derived as follows:
nie known feedback equation is:
A#8217;= A /1+AB (5)
where:
A#8217;=voltage amphfication of feedback stage
A =voltage amplification of usual stage
B=feedback factor; for a cathode follower will be unity because of total feedback
substituting the value of A, as given in Equation 1 in Equation 5.
A#8217;= µ*RL(RL+RP) / 1+(µRL//RL+RP)1 (6)
When RL is infinite, which in practice can be taken as a value of 10 megohms, Equation 6 is seen to immediately simplify to Equation 4.
Considering Equation 4 with values of in the range of 30 to 100, as recommended for the vacuum tubes for my amplifier, it is seen that the amplification A#8217; is very nearly unity. For a µ of 100, the amplification would be only 1% less than unity.
Also, the cathode input impedance of section 3, 5, 9 is very high because of the near infinite plate load impedance provided by constant current generator 10. This imposes no appreciable shunting effect on section 2, 4, 7.
Zk = RP+RL /µ+1 (7)
The numerical value of the cathode impedance Zk, looking into catbode 5 and ground, which is in shunt to the impedance of constant current source 6 as a load for section 2, 4, 7 is:
in which all terms have previously been defined.
Since RL is nearly infinite, so is Zk from Equation 7.
The ampliflcation of input signal e1 is equal to the product of the gains of both sections of tube Ia. The gain of the first section was given by Equation 4 and of the second section by Equation 3. Forming this produet to give the amplification Ae1, we have:
Ae1= µ *X(µ+1)=µ / (µ+1)(8)
(The same binomial in numerator and denominator cancels out.)
The amplification of input signal e1 is also=µ, from Equation 2. Thus, equal differential amplification is provided both input signals e1 and e1 by my amplifier stage of Fig. 2.
The above discussions indicate how constancy of amplification is maximized in my amplifier. We now turn to a consideration of its linearity, or fidelity of amplification.
Fig. 4 shows the known plate-voltage, plate-current characteristic for a triode vacuum tube such as 1 in Fig. 1, or either of the triode sections of dual tube 1a in Fig. 2. As is known, the curves for the several grid voltages, EC, run together at low values of plate current. Dotted line 35 indicates a typical load line of the prior art. This gives the correlation between the grid and plate voltages and the plate current for a given conventional load impedance RL. It is seen that the increment of plate voltage or of plate current for an increment of grid potential of from #8212;4 to #8212;5 volts is only about half that for the increment from 0 to #8212;l volt. This, of course, indicates serious distortion for any signal waveform that extends from a grid potential of from approximately 0 to #8212;5 volts. When constant current source 10 of Fig. 1 is employed, it is seen that the load line in Fig. 4 would be horizontal; i.e., line 36. |
| Ampzilla |
Posted - 2011/05/08 : 23:29:53
Nu fortsätter informationen
(För dom som inte har varit med från början så har dessa förstärkare endast varit för militärt bruk och kalibreringslab.)
Part 2
ULTRA-LINEAR D.C. AMPLIFIER
Henry 0. Wolcott, ,
Single End Push Pull
His invention relates to an amplifier that is effective down to zero frequency and is characterized by a high degree of fidelity of reproduction of an input signal and by a high degree of constancy of the amplitude of such reproduction.
While amplifiers employing negative feedback with vacuum tubes or transistors have been practical devices for many years the stability required of certain electronic apparatus in this day cannot be supplied by known embodiments of such devices. For example, in calibrating a digital-indicating voltmeter having four or five integers, an amplifier with an amplitude stability of 0.01% is required in combination with a similarly table signal source. Unless this is obtained the last decimal place on the voltmeter will flutter between two values. If the operator is attempting to measure 10.000 volts, say, this might mean recycling of the whole register between 9.999 and 10.000, under which conditions calibration is inconvenient.
I have evolved amplifier circuits having stable amplification without the use of feedback. Such circuits are invaluable in applications where negative feedback cannot be used, as in bridge oscillators. Also, where negative feedback can be used, my amplifiers give an additional order of stability; i.e., they are ten times more stable.
The gain of known amplifiers has invariably been affected by the life cycle of the vacuum tubes employed, or by variation of almost any of the components employed in the device.
I am able to overcome both of these shortcomings by providing a novel circuit in which the amplification of the amplifier is determined solely by an invariable parameter of a vacuum tube; its amplification factor. The crowding of the family of grid voltage curves in the plate-voltage plate-current characteristic for values of low plate current for a vacuum tube is well known. This, of course, results in distortion. While such distortion can be minimized by feedback, this means cannot always be employed, as has been mentioned. I am able to avoid this region of distortion by employing a network that gives essentially infinite impedance for the plate circuit load. The bad line upon the characteristic just mentioned is then horizontal. A number of known vacuum tubes have very precisely equal increments of plate voltage between equal increments of grid voltage for such a load line. Thus, feedback is not required in my circuit for an exemplary degree of linearity; or, if used, a very high degree of linearity is obtained. This aspect of my invention results from the use of a constant current source in the plate circuit of a vacuum tube if the amplifier be single-ended and there and also in the cathode circuit of the amplifier be of the differential type. A constant current source has, in effect, an infinite impedance. I embody such a source in the form of a single active element, such as a transistor or in the form of an additional vacuum tube.
An object of my invention is to provide a highly stable and highly linear electrical amplifier.
Another object is to provide such an amplifier devoid of feedback loops.
Another object is to provide an amplifier having a high impedance differential input.
Another object is to provide an amplifier which has a gain dependent only upon a structural parameter of a vacuum tube.
Another object is to provide a relatively simple and inexpensive amplifier which operates at nominal supply voltages. Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawings, in which are set forth by way of illustration and example certain embodiments of his invention.
Fig. 1 shows a single-ended embodiment of his amplifier with a generically indicated constant current generator,
Fig. 2 shows a differential embodiment of his amplifier with generically indicated constant current generators,
Fig. 3 shows the same with transistors employed to form constant current generators,
Fig. 4 shows a plate-current plate-voltage plot for a vacuum tube and an illustrative load line according to my invention,
and
Fig. 5 shows a differential embodiment of his amplifier with vacuum tubes employed to form constant current generators.
In Fig. 1, numeral 1 represents a vacuum tube, typing cally of the triode type. This is preferably of the medium (30) to high (100) mu type having a frame grid construction, such as the 6CM4 or one-half of a 6DJ8 type. The input signal e1 is normally applied between grid 3 and signal ground 30, but may also be applied as e5 between cathode 5 and the signal ground. Signal ground 30 may be an actual ground, or common circuit return, as it has been shown schematically; or it may be a point of fixed potential with respect to the input signal when this is an alternating potential, as can be established by a bypass capacitor.
Cathode 5 is connected to the signal ground through resistive impedance 12, which provides the desired cathode bias. Resistor 29 provides a return path for grid 3 to signal ground. Plate 9 is connected to constant current source 10, which in turn is connected to plate energizing potential source 8. Output terminal 11 is the means by which the output signal is taken from plate 9; constant current source 10 acting as the load impedance.
Since the output of my amplifier appears across an effectively infinite impedance, an external impedance, such as 31, that is connected to terminal 11 and signal ground, must also have effectively infinite impedance lest the loading of the external circuit reduce the performance of the amplifier. Consequently, the external impedance 31 should consist of the grid of a vacuum tube, such as a cathode follower, the gate of a field effect transistor, etc. Since an #8220;infinite#8221; plate load of 100 to 1,000 times the plate impedance of the tube 1 is satisfactory, a commensurate impedance 31 is satisfactory if it is in the megohm range.
to be cont. |
| Ampzilla |
Posted - 2011/05/02 : 21:54:15
Jag fortsätter :)Men ni får vänta till Lördag kväll
Så ni hinner läsa och smälta denna första informationen.
Jag fortsätter till helgen, måste först se till att båten blir klar till lördagens sjösättning.
Angående en transistor version så har jag en transistorförstärkare från en annan tillverkare som jag labbar med som använder både negativ och positiv feedback ( inte gjorda för hifibruk) men det får eventuellt bli i en annan tråd senare.
|
| Gubben i Kalmar |
Posted - 2011/05/02 : 11:39:13
Du får inte sluta nu!
|
| Circlomanen |
Posted - 2011/05/02 : 11:03:43
Jag måste fråga om det finns nån förenklad transistor-version?
Rör i all ära men jag är mer van vid att tänka i transistor-banor. Jag har svårt att linda skallen runt denna konstruktion då det är en massa bias-kretsar mm jag inte omedelbart förstår. Det är förvirrande för en grusälskare som mig.
Det är en helt klart mycket intressant förstärkarteknik, även om jag blir en aning irriterad på säljsnacket i artikeln. Jag förstår att en hel del skrevs just för att göra reklam och framhäva hans konstruktion, men jag håller inte alltid med. Saker har rört på sig sedan början av 60talet. Framförallt med transistorer.
Detta kommer tyvärr plåga mig idag. Jag kommer vilja rita, skissa och ändra runt tills jag fått en förståelse för alla aspekter av kretsen.
Jag har redan börjat circlotronifiera denna koppling.
Mvh Johannes. |
| Bubbel |
Posted - 2011/05/02 : 09:40:03
Jag har inte kommit halvvägs ännu och såg fram i mot resten själv är jag ingen höjdare när det gäller att konstruera förstärkare men lära sig kan man alltid göra.
Du får inte sluta nu!
Anders |
| everwake |
Posted - 2011/05/02 : 08:49:23
inte sluta nu, de flesta av oss vill nog bara inte sabba tråden med kommentarer, kanske någon mod kan lyfta ut innehållet till en separat artikel i ett senare skede? |
| Circlomanen |
Posted - 2011/05/02 : 07:33:53
Du får inte sluta nu.
Jag har precis kommit igång med att grubbla på och knåda hans konstruktioner. Detta är mycket intressant, även fast det är något tungläst. Det får nog bli en och en annan skiss för att klura ut det hela..
Mvh Johannes.
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