Valve Crystal Oscillator Grid Current

[John M0GLN]

Thanks for all your comments, especially to Al & Lawrence for the explanations, while I understand most of what has been said , there are still a couple of points that I'm not clear on..

First, why does the test rig that Al built only take 1mA of grid current although more or less the same circuit from my book take 40mA? The only real differece I can see is that there is some cathode bias in the former.

And how does a valve like a 6F6 supply 40mA from its control grid? Just looking at the RCA page showing 'Typical Operation and Charcteristics' it lists a 'maximum signal plate current' of 40mA.

Thanks

John