My apologies, I was wrong. If the ECH42 can be used as a combined AF amplifier (triode section) and phase inverter (hexode section), than like you I don't see any reason why the ECH80 couldn't.
I just found out I even have a schematic of an amplifier in which the ECH42 is used as amplifier/phase inverter, but a little different than in the datasheet. The anode of the hexode setion is grounded while grid 4 is acting as the plate. Maybe this is done to prevent problems caused by secondary emission from the plate.
The ECH4 and the ECH21 were sometimes used as combined AF amplifier and phase inverter, just like the ECH81 sometimes was. Attached two examples, one from a book by Philips (1942) and one from a book by Ratheiser (1955).
I just found out I even have a schematic of an amplifier in which the ECH42 is used as amplifier/phase inverter, but a little different than in the datasheet. The anode of the hexode setion is grounded while grid 4 is acting as the plate. Maybe this is done to prevent problems caused by secondary emission from the plate.
The ECH4 and the ECH21 were sometimes used as combined AF amplifier and phase inverter, just like the ECH81 sometimes was. Attached two examples, one from a book by Philips (1942) and one from a book by Ratheiser (1955).
Attachments
No worries…
I very much appreciate all the replies.
After i drew the internal structures on a piece of paper and for both ECH80 and ECH81 and examined the ECH42 data sheet it seemed that it could not make sense otherwise.
I have quite a few 6M5 which are identical to EL41 being common here in Australia. So i think it would be worth trying that first example you have generously shared.
Coming back on the use of the ECH42 as a combined AF amplifier and phase inverter in the Fapesa A7 circuit: I should have written that by connecting the plate to ground, g2 and g4 are acting as the plate instead of only g4.
The cathode, grid 1 and grid 2 constitute a triode. I wonder if Ig2+g4 is still being influenced by signal on g3. Part of the electrons will pass through g2 and than enter the space where g3 is active. But where could these electrons eventually go? With the anode grounded, an electron either reaches g4 (even when it would initially pass through g4 it would be forced back to g4 by the grounded plate) or gets repelled back to g2 if the voltage on g3 is low enough. So whatever happens, the electrons seem to allways become part of Ig2+g4.
The cathode, grid 1 and grid 2 constitute a triode. I wonder if Ig2+g4 is still being influenced by signal on g3. Part of the electrons will pass through g2 and than enter the space where g3 is active. But where could these electrons eventually go? With the anode grounded, an electron either reaches g4 (even when it would initially pass through g4 it would be forced back to g4 by the grounded plate) or gets repelled back to g2 if the voltage on g3 is low enough. So whatever happens, the electrons seem to allways become part of Ig2+g4.
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I may be quite incorrect on this but it looks to me as if it functions like a twin triode with a common cathode.
However with the screen of the hexode acting as the plate ( the real hexode plate being tied to ground).
Now usually the screen in a pentode and I’m guessing the screen in a hexode will not be able to a lot of current.
It’s possible though i haven’t tried to analyse it that there may be half a milliamp ‘plate’ current in this pseudo twin triode, so the screen may well be within its current limits.
Does this make any sense?
However with the screen of the hexode acting as the plate ( the real hexode plate being tied to ground).
Now usually the screen in a pentode and I’m guessing the screen in a hexode will not be able to a lot of current.
It’s possible though i haven’t tried to analyse it that there may be half a milliamp ‘plate’ current in this pseudo twin triode, so the screen may well be within its current limits.
Does this make any sense?
It makes sense to me. I was mostly writing about what happens in the hexode part when the plate of the hexode part is grounded. But if the hexode section starts to work like a triode, than the whole tube is indeed a double triode.
In tubes like this Ig2+g4 often is in the order of the plate current so I wouldn't worry about the current capability of g2+g4 when using it like a triode. Furtermore I think that the Argentinian "Fapesa" was part of the Philips concern (hence the use of "Miniwatt" in the document). I would think they would not publish this type of use of the ECH42 when it would violate maximum values.
In tubes like this Ig2+g4 often is in the order of the plate current so I wouldn't worry about the current capability of g2+g4 when using it like a triode. Furtermore I think that the Argentinian "Fapesa" was part of the Philips concern (hence the use of "Miniwatt" in the document). I would think they would not publish this type of use of the ECH42 when it would violate maximum values.
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