That is sooo cool.Danhalen wrote:
Yup no resistor, just the .68 cap. Is that bad?
I believe what's happening is something called space charge biasing or something like that. In a regular setup, the resistor on the cathode makes the voltage potential at the input grid relatively negative (why you don't need bias voltage like you do for the power tubes whose cathodes Are tied directly ground) Since pre amp tubes have plate resistors you're not going to damage anything by connecting the cathodes straight to ground (the plate resistors limit current) but in theory you shouldn't get any sound. However I did the same thing once to a tube based preamp pedal (at 250v plate voltage) and it worked and sounded great. So yeah, it does work despite logic, shouldn't be dangerous at all. Never thought to try it in a real amp though hmmmmm.
(Note: don't try this on a power tube without proper bias circuitry OR an appropriate cathode resistor - as the OT in place of the plate resistor won't limit quiescent current and stuff will blow up guaranteed)
Was the .68 cap between ground and the cathode? That might in theory charge the cap up to full B+ voltage at the cathode kinda throwing out my space charge theory. However, as long as a sufficient plate resistor like 100k is still in there nothing should blow up. Still very cool that it works at all and sounds good.
I'd love to hear some clips.
I did however have the v1b cathode going straight to ground at one point by accident. It actually sounded pretty cool but I much prefer the setup I have now which is the one at the bottom of the first page of this thread. Essentially bass spec, 220uf on V1 shared cathode, 100pf bright cap, .022's in the PI, and lower filtering 50uf mains, 32uf on everything else. 27k negative feedback on the 8ohm tap. No bypass cap on V2. I really should try and get some good clips up. I have some stuff from practices but it is really low fi and doesn't sound like anything really.