Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on February 06, 2013, 12:44:10 am

Title: pf value cap from 12AX7 plate to cathode?
Post by: 12AX7 on February 06, 2013, 12:44:10 am
Didn't wanna hijack that other thread about sluckey's  dual preamp marshall. But i had a question about it. I think the 100pf cap on V2A from the plate to cathode is to tame high end, right? if so, what is the difference between that and using a cap across the plate resistor instead? Or IS that plate>cathode for something other than taming high end?
Title: Re: pf value cap from 12AX7 plate to cathode?
Post by: tubeswell on February 06, 2013, 03:45:38 am
Didn't wanna hijack that other thread about sluckey's  dual preamp marshall. But i had a question about it. I think the 100pf cap on V2A from the plate to cathode is to tame high end, right? if so, what is the difference between that and using a cap across the plate resistor instead? Or IS that plate>cathode for something other than taming high end?

They're both doing the same thing, because they are both bypassing the plate and shunting some HF to 'ground' (either via the B+ and thence through the filter caps to ground, or 'more directly' via the cathode)
Title: Re: pf value cap from 12AX7 plate to cathode?
Post by: 12AX7 on February 06, 2013, 12:59:26 pm
Thats what i figured. I guess they sound a bit different which would be the only reason i can see that people don't all just use one way. I think i'll have to try this myself in place of my current parallel plate cap.