I was fooling around some more with my cathode drive and found if I unground the top tube and feed it as well, my drive requirement goes down by 6dB and FFT shows a LF rolloff of 18dB/octave rather than 6dB/octave with straight cathode drive.
Is there a name for this?
Is there a name for this?
An externally hosted image should be here but it was not working when we last tested it.
It is, and that's what you've done. By feeding out-of-phase signals to the cathode and rid of the upper tube, you've introduced positive feedback. So your gain is doubled, just what you saw.
Not twice, but dependant on what signal is present at the 6080 plate. I haven't done the algebra, but it would certainly be interesting if the signal always happens to be so. Come to think of it, with mu = 2 in the 6080, a gain of -1 could easily happen, so yeah it would about double the signal. For a higher gain tube like say, 6LQ6, it should have higher initial gain and only somewhat higher gain with this arrangement (i.e. the same increase, but a smaller percentage given the higher total gain).
Bootstrapping didn't occur to me (Geek posted this elsewhere first 😉 ), but it makes sense in a roundabout way. Bootstrapping is mostly a case of NFB, like CF with bootstrapped grid leak to increase input impedance, but PFB, I don't see why not. 🙂
Tim
Bootstrapping didn't occur to me (Geek posted this elsewhere first 😉 ), but it makes sense in a roundabout way. Bootstrapping is mostly a case of NFB, like CF with bootstrapped grid leak to increase input impedance, but PFB, I don't see why not. 🙂
Tim
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