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abbot
Member
662 Posts |
 Posted - 2021/12/22 : 22:12:19
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Apropå patent på pentod:
"The triode had namely two serious drawbacks. First of all it didn#8217;t behave like a current source. In other words, the anode current not only increased with increasing grid voltage, but also with increasing anode voltage. In bipolar transistor terms we would say: #8220;it had a low Early voltage.#8221; This seriously limited the maximum amplification and the output power of the tube. At the same time there was a strong capacitive coupling between the anode and the grid. This Miller capacitance limited the high frequency operation.
In 1915, a remedy to these drawbacks was found by an old acquaintance of us: Walter Schottky. By inserting a screen grid in between the control grid and the anode, which was held at a constant high potential, the anode potential is effectively screened from control grid. In its hybrid form this arrangement is of course still widely used, and is known as a cascode. The tetrode as is was called, represented an enormous improvement, but in its turn also had a drawback. Electrons accelerated by the high potential on the screen grid bombard the anode and generate secondary electrons.
Unfortunately, in operating conditions where the anode voltage is low compared to the screen grid, these secondary electrons are accelerated to the screen grid, causing a current flow in the opposite direction. The result is a kink in the anode current characteristics, not unlike the kink in SOI MOSFET#8217;s. The problem especially occurred in output stages where the output voltage would swing between supply voltage and almost zero. Tellegen studied the problem, and came up with a very simply solution.
He simply inserted a third grid between the screen grid and the anode. This brake- or suppressor grid was connected to a low potential e.g. the cathode. The suppressor grid simply pushed the secondary electrons back to the anode and all at once all the disadvantages of the tetrode had disappeared. The pentode was a near ideal amplifying device with very high amplification and capable of delivering high output powers at relatively low voltages. Tellegen and Holst immediately applied for a patent on the 14th of December 1926.
It turned out to be perhaps the most valuable patent of Philips ever. Philips sat on the patent like a tiger protecting its young. In 1927, Philips becomes the largest radio tube manufacturer in Europe. Because of the pentode patent the European market was not interesting for the Americans at all. As a result the European and American tube markets developed almost independently, with different type numbers, envelopes, sockets etc. The protectionism of Philips was so strong that they would even order confiscation of radio tubes that radio shop owners directly imported from the U.S.! In 1932, little more than 10 years after the first samples were made at the research lab, Philips produced it#8217;s 100 millionth#8217;s radio tube".
Från: https://www.dos4ever.com/SAFE/SAFE.html
Även den här länken leder till intressant läsning, inte bara om röret i rubriken: https://www.dos4ever.com/EF50/EF50.html
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Erik Andersson
Member
1950 Posts |
Posted - 2021/12/23 : 09:39:37
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| Bör kanske tilläggas att Philips,Telefunken,Marconi och några till bildade en trust och krävde höga avgifter av radiotillverkare när de använde sig av deras patentsökta rör och kopplingar. Vissa av dessa patent gick ut först i sent 1950 tal |
Medverkade till den nya "rörvågen" på 1980 talet
erikasson@telia.com
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Erik Andersson
Member
1950 Posts |
Posted - 2021/12/23 : 12:11:57
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| Ett tillägg till. Om en pentod/stråltetrod arbetar med en i förhållande till anodspänningen låg skärmgallerspänning får vi mer eller mindre beroende på spänningsskillnaden ett amplitudbegränsarsteg. Det kan fylla sin plats ibland men definitivt inte i våra förstärkare! |
Medverkade till den nya "rörvågen" på 1980 talet
erikasson@telia.com
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soundbrigade
Semesterfirare
7879 Posts |
Posted - 2021/12/23 : 15:23:08
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quote:
Bör kanske tilläggas att Philips,Telefunken,Marconi och några till bildade en trust och krävde höga avgifter av radiotillverkare när de använde sig av deras patentsökta rör och kopplingar. Vissa av dessa patent gick ut först i sent 1950 tal
Men varför så många pentodrör tillverkade i Sovjet?? Alla patentavgifter måste ha gjort stora hål i den sovjetiska statskassan, eller har jag missat något ....  |
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abbot
Member
662 Posts |
Posted - 2021/12/23 : 20:00:44
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| Nej, hela du är en enda fullträff! |
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