Tube Amp Archive

Super helpful replies. Thanks, guys!

Looks to me like the 6G3 channel will need a 180K NFB resistor, and the black channel will require an 82K, to go with the 5K presence pot.

I’ll redo my layout to add the 100nF coupling caps, and to move my mixing resistors closer to the PI.

Ok, I can see there is more to this than just my drawing error. I’ve thrown a 5K pot in there without adjusting anything else. I’ll do some reading and see if I can figure this out.

Thanks for your reply, PDF64. I just noticed I drew my 820r/56K NFB resistors twice by mistake. I’ve corrected my drawing.
Does an issue still remain?

Hey guys, I’ve ripped apart my 2nd(of 4) build (6G3) to combine the 6G3’s bright channel with a blackface deluxe bright channel. No Trem, no ‘Verb. Up until now I’ve built from kits. This is my first build drawing the layout myself. I think it seems ok… one thing that concerns me is the long lead th...

Ok, so I swapped the OT leads and… She works! Sounds great! Lively, rich cleans, an impressive amount of overdrive, I’m happy! This has been a great experience building the amp, and troubleshooting. I can safely say I have a better idea of what goes on in an amp after getting this vibrolux operation...

Is that what that might be? I knew I might have to swap the OT wires but thought I’d be hearing more of a howly feedback. I got the wires right the first time with my 6G3 so I’ve never heard the oscillation before.

I’ll disconnect the NFL tomorrow and report back.

Hello again guys, My buddy and I just finished another session, and got V2 running, after replacing the socket. We measured the appropriate 50V off the phase inverter cathode. We also measured 20v going into the phase inverter grid, but based on something we read on valve wizard, we think we should ...

Hello Stevem, Points taken on the filament wire and soldering. I do believe I’m getting voltage on all the filament pins, but I had not considered that the tight winding (perhaps I will go back and redo the wire between output tubes, I was never happy with it) could be causing issues. I agree I need...

Here you go,

Still no voltage.. V2 filament is not glowing. I dismissed this possibility since I was getting 6.3ish onto the filament pins. Looking at the empty tube socket, tube pin receptical #1 looks to be damaged - it’s not got that football shaped opening that the others do. Gonna guess this may be keeping ...

Sluckey,
V2 pin 3: 1.43k
V2 pin 8: 59.4k

Sluckey,
No, not yet. I went back and checked for continuity/resistance values along every point of the 12ax7 cathode to ground paths and everything seems to check out.

So, I’m not sure what’s up!

Hey guys, thanks again for the replies, Martin, sorry for the confusion. I meant to say, each tube’s filament glows, whether in socket V3 or V4. But I found out what was happening - I wasn’t getting a bias voltage on V4’s grid pin, nor a range of plate voltages with the adjustment of the bias knob. ...

Alright, so I have determined that the issue of one 6v6 not heating up is socket specific, not tube specific. Also, I see both filaments glowing, regardless of the socket it’s in. I replaced the 10k in the bias circuit with a 33k and my plate voltages went up a bit - to 285v plate V3(the cold tube s...

Thanks for the replies, guys, With only the 5Y3 in, my power tube grid pins (and also the negative lead of the bias cap) are showing me a range of -39 to -49vdc (bias pot). I’m guessing -49vdc is going to stress that 50v bias cap… I’ve only got the 200w bulb for the limiter so I just went with that....