Tube Amp Archive

Hope this helps. I got this years ago and don't remember where and can't vouch for accuracy but I just scanned in the printed copies I had made. Let me know how it goes. I also had a Pacesetter until last year which was the same circuit in a combo. Great amps (at least the non PCB ones I have had) ...

Dirty low input jack contacts

That's the export power transformer, I just noticed you're outside the USA. Have you tried contacting Mesa? There are notes on the schematic that mention something about the power transformer being changed. Looks like they did something to separate audio grounds from the filament center tap on a lat...

What's the part number on the power transformer?

If you are going to run the amp distorted thru any type of time based effect like reverb , echo or chorus it will sound like crap! Go to a music store and try any amp with a loop out that way and decided for yourself! You have that backwards. You want time based effects after distortion. Running th...

The loop goes after the EQ and before the phase inverter. I usually use a tube loop unless the space is tight, then I'll use a solid state loop.
Jerry

That's cathode material.

They look like some caps I have here that came form the phone company. Are they ceramic? I have a bunch, but I haven't tried them yet.
Jerry

Toilet paper roll makes a nice cover for the cap with B+ on the can. That with some electrical tape and some hot glue or RTV to hold it on and you're all set.
Jerry

Cap on the bias pot is installed backwards.
Jerry

This makes no sense. The outer terminals of the pot feed the power tubes and you said those have -43v. The wiper on back is the raw bias voltage and you say that is -22v or -2.8v not sure which one is correct there. Did this amp blow fuses before you changed the caps? Is the bias cap on the pot inst...

The only way I can see the PI ground affecting power tube bias is if the PI coupling caps are leaky. The anode voltage will rise if no current is flowing, and of course pulling the PI tube would have the same effect. Try lifting the ground on that resistor and watch what happens. Seen it in my shop...

Were the power tubes actually new or just another set you had? Have you tried a third set just in case the new tubes had a bad one? Check the 100 ohm resistor on the tail of the phase inverter and check the solder joints there to ground. Seen a lot of Fender amps with a broken solder joint here that...

None of them. It's quite a bit different from any Marshall. The preamp is somewhat similar to a hot rodded Marshall, but not a copy of anything. Phase inverter is not the typical long tailed pair and the power tube suppressor grid is connected to bias voltage not ground. Pretty cool amps. Sounds bes...

Yup, in the old pics you had the ground layer still on the center conductor. You have to trim or scrape that off. It's conductive.
Jerry