Tube Amp Archive

I agree- but this is a transistor/solid state amp, so no output transformer to worry about!

BTW, I haven't become too familiar with it yet, but I used my scope to trace voltage at the transformer secondary under no load (1), with the power on + no speaker load (2), at the -43V rail under half mains (3) and at the output on half mains with no load (4).

Hi there, I have a Gallien Krueger bass amp (schematic attached) on my bench that was distorting on low notes (on a bass guitar). The bias was a tad off so I adjusted it to 5mV and was checking other voltages inside the amp when I noticed that the power transformer has started buzzing way more than ...

Great, now I'm going to have nightmares.

Seriously, though, thanks for your help!

Yeah, I've cleaned up a lot of grounding issues and the hum is still there. I even elevated the heater CT just to be safe. I was wondering about that too- how the hum can be present without the reverb tank connected and without V2? But still be dependent on the reverb knob setting? I'm going to take...

That's the one I grounded- I figured it was more sensitive since it was essentially a long grid line. The chassis sits on top of a sealed 10" cab with the reverb tank inside it at the bottom so it shouldn't be bothered by the trannies. I tried turning the tank the other way around inside the cab jus...

Ok, I've isolated the rca shields and grounded one of them with the RT ground at the common cathode ground for all preamp cathode and grid leak grounds, which is then earthed to the chassis. This ground point also collects the pot grounds (Trem depth>Trem freq>Reverb>Volume>Input Jack>Ground). I use...

Sorry again! I've attached it this time. Mark- I'm already using shielded wire for the return line from the RCA to the grid of V2B. The 220k resistor between V2B and V1B makes an unshielded run of about 2 inches from the reverb pot to the 3.3M junction, where shielded wire is used to the V1B grid. N...

What I meant was, the RCA jacks are themselves isolated but I had run ground wires from both rings to ground, defeating the purpose of isolated jacks! Thank you for your suggestion. However, I'm using a 4x20uf multican filter cap, which has a common ground for all stages. I know this isn't ideal for...

Yes, they're both isolated. I have both rings of the RCA jacks grounded to the chassis along with the -ve end of the RT secondary, though. Since the reverb tray I'm using has both rings connected (through the tray chassis, I presume), does this create a big ol ground loop? I'm guessing yes...

Sorry! Try this one:

https://docs.google.com/leaf?id=0B5eUEw ... ey=CKut4jQ

Hello, I'm hoping (pleading?) that someone can help me with my build. It's a 2x6V6GT, 3x12AX7 build with reverb and tremolo and it's working fine except for a low, loud hum when the reverb knob gets turned up above zero. The hum is present even when the reverb tank and V2 (reverb driver & recovery) ...

Hi there. I have a Fender Frontman 212R that was humming when nothing was plugged into either input or the power amp in (FX return). Otherwise, it worked fine and the guitar signal was as it should be. Here's a schematic for reference: http://docs.google.com/leaf?id=0B5eUEwCoF9tVMWM2OWY5ZmQtYjI3ZC00...

Never mind- solved it! It was the reverb tank after all (output coil is open circuit). Funnily enough, the tank had been connected backwards, so the *input* end would pass a signal back to the return on the amp. When I first checked the tank, it was measuring the correct DC resistance on the input s...

Hi there, Does anyone have a schem for a Pubster 25 110 or even a Clubster? I'm not getting any signal into the reverb tank, although the tank itself and return line are working fine. Also, it seems like the treble and bass controls are not working at all, although the mid is fine. The 12ax7s test f...