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Originally Posted by adibrook
As far as i understand g3 is the audio input. I just left it unconnetcted, although i guess a high value resistor to ground to stop it floating would be usefull.
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All pins of an active valve must always be connected to *something*, no matter what the application. The valve doesn't know how you intend to use it. Unconnected pins gives *completely* unpredictable results, since the electron stream can both discharge and build up a voltage on a floating electrode. Read: The valve ends up not doing as you intended.
Connect g3 directly to ground for now, you can save the resistor for later.
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Originally Posted by adibrook
There is a 0.1uf cap between ht and earth. (not marked). The 50k pot is pretty useless, and was just there for experimentation.
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Did you pause to consider
why the pot was useless?
If you don't have a capacitor *directly* at the g2+g4 pin, the RF current pulses on that pin will have nowhere to go as you adjust the pot, because of the increasing resistance blocks the pulses from using the 'common' anode supply bypass resistor. This devastates the RF amplification of the valve, since the g2+g4 voltage is no longer reasonably stable.
Which begs the question: Am I just wasting my time when I reply to your questions?
When I tell you that you
need a capacitor connected so-and-so, do you read this as it being optional? Should I use stronger language to get the message through?
Many circuits *does* *not* work well or if at all if you make your own reinterpretations just because you feel like it (unless you are certain you understand how it works and takes this into account). This is particularly true for RF.
Frank N.