Tube Amp Archive

Ok- I've lifted the B+ return from the effects loop card and verified via DMM that there is no other (unintentional) connection to the effects loop card (it it measures many tens of kohms to over a meg). I then connected an alligator clip to the B+ return on the effects loop card, and connected it t...

So < 0.5%. That's typical, if not on the low side. The +/- spikes look like they are from the input side of a FWB rectifier. Thanks martin - That makes sense, since the period of the pulses in the second scope trace are 1/120Hz, not 1/60Hz (and they go both + and -). There's only 1 FWB rectifier in...

Thanks Roe, that's good to know. It looks like I'm at about 2V ripple on a ~380V B+ supply for my power tubes.

I'm now sure that my problem isn't B+ ripple. Since when I ground the output of the effects loop buffer, the buzz disappears. just gotta figure out how that buzz is getting in there.

Thanks again xtian, and thanks for that reference too. I will have to do some reading up! There are several rectifiers in this amp: the main B+, the negative bias voltage, and a lower voltage 12V that gets regulated to 5V for my switching relays. All rectifiers live on that card in the bottom sectio...

Thanks xtian! It's kind of fun getting back into this, especially now that I have actual test equipment at my disposal. And I'm super stoked at how good this amp is sounding already. I did something right ten years ago lol. FYI I don't think anything is getting in at the PI anymore. grounding the si...

Ok, well it's not the ripple on the B+ going to the plates, I can confirm this. This new scope trace is of the plate of one side of my PI. https://live.staticflickr.com/65535/49924222656_6f89e4f96e_w.jpg The other side shows similar spikes, but not quite as severe. When I AC ground the PI plates thr...

Hi guys, have been out of the homebrew amp community for probably >10 years; I used to be fairly active on AX84 and apparently here too, as I had an account I logged into! Quarantine has seen me resurrecting an old amp I never finished with all the equipment from the office I now have at home. It's ...