vinyvamos

heptode/pentagrid compressors and ECH8x tubes
« on: July 05, 2020, 06:48:41 PM »
Is there anything to say that a pentagrid compressor cannot be built around a pair of ECH81 or ECH83 with the cathodes grounded, and the triode sections used as the next gain stage? A reference negative grid bias would be needed on both the heptodes and triodes due to the cathodes sharing a pin. Or... how about using LEDs to ground from the cathode pins to provide a fixed bias point, which would have to suit both sections of course. Or would this simply not work? I am assuming here that the use of LEDs means that no bypass caps are needed and that the voltage will be constant regardless of changes in Heptode current during gain reduction.

On that topic, how does the heptode cathode current vary WRT gain reduction compared to a more common vari-mu triode/pentode stage? Is it pretty much the same scenario?

Why were pentagrid compressors forgotten about? Do they exhibit higher distortion/lower GR capability than the later designs using triodes and pentodes?
Atomic Analog Devices
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abbey road d enfer

Re: heptode/pentagrid compressors and ECH8x tubes
« Reply #1 on: July 08, 2020, 12:33:21 PM »
Is there anything to say that a pentagrid compressor cannot be built around a pair of ECH81 or ECH83 with the cathodes grounded, and the triode sections used as the next gain stage? A reference negative grid bias would be needed on both the heptodes and triodes due to the cathodes sharing a pin. Or... how about using LEDs to ground from the cathode pins to provide a fixed bias point, which would have to suit both sections of course. Or would this simply not work? I am assuming here that the use of LEDs means that no bypass caps are needed and that the voltage will be constant regardless of changes in Heptode current during gain reduction.

On that topic, how does the heptode cathode current vary WRT gain reduction compared to a more common vari-mu triode/pentode stage? Is it pretty much the same scenario?

Why were pentagrid compressors forgotten about? Do they exhibit higher distortion/lower GR capability than the later designs using triodes and pentodes?
What do you expect from using such a tube over a simple remote cut-off triode or pentode?
These tubes were designed to solve problems particular to superhet receivers, in particular assuming two functions in one (oscillator and mixer).
In a vari-mu compressor, the extra grids would be tied to other electrodes or to fixed voltages, which would result in operation similar to a triode or pentode.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
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