The Amp Garage

Measured the bias today, the voltage drop across the bias resistors (which I measured to 1.2 ohm) was 55 mV. So the bias current is 55 * 1.2 = 66mA. Probably too hot, right? I then attempted to measure the plate voltage (pin 8) with one lead of the multimeter touching the pin, and the other clipped ...

Thanks again, Romberg, I would like to buy you a beer for all your help! Thanks to everyone else who has chimed in as well. I played the amp for about an hour yesterday. Was not really able to put it through its paces, because even with the attenuator at max, this amp is LOUD! It does seem to react ...

Disconnected the NFB wire from the 8 ohm jack, and for the first time I have sound! Still a fairly high level of hiss, but before I do more troubleshooting or re-connect the presence control, I'm going to play the amp as it is. I made a soundclip, what's the easiest way of posting it here? And what ...

Grounded R10: No sound

Removed alligator clip (regular startup): High pitched squeal with guitar connected. Without guitar, hiss and static noise, like FM radio between stations. Loud pop when turning standby switch back to standby.

I will try the alligator clips method as soon as I have some free time to devote to this project.

Just wanted to say thank you to all of you who have given so much helpful advice.

Thanks for the updated layout, rj. I did find an error in my precence control wiring, so I rewired it according to the updated layout. Started up the amp again, and now I got something completely different than the low output distorted tone, namely some very loud feedback cacophony! I assumed I need...

I did check the speaker jack wiring. I have not biased the tubes yet. I just did a new startup and adjusted the bias knob whilst playing, but it still sounds like a lofi fuzz pedal. But at least I have sound! I am attaching a new pic of my power tube, speaker and bias pot wiring. Too late tonight to...

Today I checked my work against layout and schematic, did a startup without tubes, got B+ voltages from 410 to 404, and ... (Wait for it!) bias voltage of -33! Yay! So I did a startup with tubes, but disappointingly got only low, distorted output. Anti-climax! I then tested all the tubes in a workin...

Yes, the bias wire was intentionally disconnected when I was troubleshooting. I will connect it and do a full layout/schematic check before doing a startup test. If I have learned anything from this build, it is to be especially patient when getting close to the finish line. For my next build, I wil...

IMG_2168.JPG IMG_2223.JPG Good points, I have attached the schematic and the layout I have used. Sorry for not doing that to begin with. But now I think I have located the problem. I had used a connection on the main board for the NFB resistor (under romberg's B label), because I didn't want it sus...

Thanks for all the continued advice and help. Do I need to connect a speaker load for test startups witout tubes as well?

I wondered if I had connected the speaker wires to the wrong side of the shorting jack, but after changing them over to the right, I still have continuity to ground from the bias wire. I could not see anything obvious on the main board in the R16/R17 area either.

All speaker inputs have continuity to ground even when I insert a jack. Did I use the wrong speaker jacks?

As I read the schematic, the two 100k bleeder resistors comes before the capacitors, but does it matter if I have them like this?

The white bias wire (disconnected from the bias board) also has continuity to ground, as does the junction of R16/R17 that the bias wire connects to.