The Amp Garage

That lead me to recall some prior discussions here that you are not really balancing the PI as much as the whole power amp. Is that a fair statement or am I misunderstanding? You are correct. The best approach would be to arrange the power tubes to get the best DC balance, and then use the PI trimm...

I think with 51k/47k plate loads and 22k tail as shown in the 2nd Gen layout, a perfectly matched 12AT7 would have very nearly balanced outputs. Any particular tube might be off in either direction, so keeping the original offset in place with a +/- capability via the trimmer would be the way to go.

Frankly, I'm sick of this. If you don't believe it or refuse to try it, good for you, whatever... Marc clearly heard a difference, as have numerous other folks, I applaud him for trying it for himself and making up his own mind. I have never said that I don't believe it makes any difference (and I ...

While waiting on some parts to arrive I "balanced" the PI. Scare quotes because with the 5K trimmer I installed and the tubes in the amp, I could get close using the ampeg method but not all the way to a 0v offset. It settled around 1.7. I do have another 12AT7 and may try that to see if it gets me...

Replaced rectifier diodes, no change in how it acts. B+ back up to 420vdc range with +/-2vdc drift. Transformer too hot to touch more than a few seconds, maybe 110°F to 120°F. PT's biased to ~15watts (36 mA @ 420 volts).voltages periodically. Still can't figure out why B+ is now 25 volts less than ...

I have to mention how I’m always surprised by the differences in preamp voltages dependent upon the given tube and position - and how they interact both voltage and sound-wise. Below is the combination I like today, lol. Tubes will typically have so much variation in current that the voltages will ...

I currently have it going to the OD relay NO2 per the board plans - but nothing connecting to that cap on the board. I think I’m going to try a jumper from OD relay NO2 to that cap.... Going to try the simplest way first and jump relay to board. That's it. The Eyelet board plan relay connections sa...

Just OD; and with everything maxed out and PAB on. Worst (or best) case for starting an oscillation. Try chopsticking and see if you can make anything change. How would I drive the power amp with 102? Preamp out from 102 plugged into power amp in on BM? Would I use regular cables or speaker cables?...

The OD section volume acts more like a master and the Drive like a pre-amp volume; but even cranked all the way up - still weak. If I dime the master, OD volume, and drive (and pre-amp volume) then switch on PAB - I get a high-pitched whistle (oscillation?). The strange preamp behavior could be an ...

No slight intended, I just thought it made an interesting plot.

Speedypancake wrote: ↑Sat May 18, 2024 9:39 am Can you help me turn it into a simple overdrive circuit to replace the Guyatone pedal??

Guyatone tube pedal? There are a couple of versions: https://juggbox.blog.jp/archives/15803877.html

When the voltage drop across the MOSFET is larger, the voltage on the tube plate is smaller. When the voltage on the tube plate is smaller, the tube draws less current. So when the drain-to-source voltage increases, the drain-to-source current decreases. Let's graph that: MOSFET Dissipation 1.JPG T...

Well, it looks great, anyway! Your lack of OD may be some wiring error in the relay switching, and it seems strange that you have to set the volume and master very high to get decent volume. DC voltages look good except for the FET, which needs a bias adjustment. BTW, the "top" and "bottom" of the F...

Seemed like I had a better balance between the channels too but that required maxing out the volume and keeping overdrive around 50%. Was a low dB test though and may not be reflective of normal playing levels. More fun later tonight after work.... I ran a simulation including source impedance for ...

Great! looking forward to seeing photos and maybe a sound clip.