Is there a name for this drive method?

[Geek]

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?

[SY]

Bootstrapping.

[Geek]

I thought bootstrapping was a type of FB?

[SY]

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.

[Sch3mat1c]

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

[Geek]

Thanks guys