Pignose mods

[yug]

Hey all,
I've been studying the schematics of the Pignose G40 and the Fender Vibro champ. Many similarities(altho', prob'ly more with the VibroLux). I want to add the vibrato circuit from a Vibro champ to the Pignose. Yeah, and the reverb, too.

Any help?

[thetragichero]

you planning on using tube or solid state gain recovery?

[yug]

Hero,
Tubes, dude, tubes. It looks to me that I will need to add a 12AX7 to the pignose for the vibrato circuit. I thought about using an existing 12AX7 but they all appear to be spoken for on the pre-amp circuit.

I grew up around tubes. My dad used to grab old TVs off people's trash heaps and fix them up while teaching himself electronics. I took the easy way and went to school. Nobody teaches tube theory anymore and my dad is gone over the rainbow. So, I'm trying to remember what I picked up as a little kid along with some books and forums like this.

I know I can do this. But, I will need guidance.

yug...

[sumgai]

yug,

If you're not intending to do this for commercial purposes, then simply copy any Fender amp schematic from about 1960 on.

The important part for the Vibrato circuit is the interfacing to the main signal line. Prior to 1960, most Fender amps actually modulated the bias voltage going to the output tubes - didn't work so well. Amps from the Blackface and Silverface eras work by modulating the signal itself before it gets into the phase inverter - a much better-sounding method.

As for the reverb, Fender didn't make amps prior to 1960 with built-in reverb, so that right there limits the scope of your search. Again, Blackface or Silverface era schematic are the ones you want to emulate.

Pretty much every component used then is still available today, so it shouldn't be impossible to duplicate either circuit in toto. Might get a bit pricey, or take some time to find the bargains, but it can be done. After all, amp repairmen still need to fix these things, right?

As for additional help, I think you'll be fine. Just remember to keep one hand in your pocket as you test any high-voltages. (IOW, make damned sure you aren't the fuse through which high-voltage, high-current is gonna flow!!) Beyond that, we Nutz can best help you solve problems as the come up - anticipating Mr. Murphy is not a fun exercise.

HTH




sumgai

[thetragichero]

i would email pignose to get the PT specs to make sure you'll have enough heater current
if they're anything like peavey, you should get a reply within a couple of hours (and this was for an amp they haven't made in 15 years!)

[sumgai]

'hero,

Good thought, but a couple or three 12AX7's aren't gonna overtax a PT that's designed to feed a pair of 6L6's (or similar power tubes) - that's a drop in the bucket, comparatively speaking.

Physically, I'd be more concerned with heat build-up. Can't have those little fire-bottles too close to each other..... Again, emulate Fender spacing, and there should be no problems. But not having a G-40 on the bench to check out for myself, I'm only guessing/hoping that there's enough room for these mods. Otherwise, a remote chassis in the bottom of the cabinet becomes a possibility.

HTH




sumgai

[yug]

So, I've refined the research to the '64 Vibro Champ. The pre-amp circuit is nearly identical to the pre on the pig. The Vibro Champ uses one 12AX7 for the pre-amp, the pig uses three. The Vibro Champ uses a dedicated 12AX7 for the vibrato circuit. I'm thinkin' that I could add a 12AX7 to the pig, tap into the power circuit for the grid and heaters and add the control pots and add it into the circuit. The only stumbler I see is that big ol' 5Y3GT rectifier. The pig has a diode bridge rectifier so they should operate in similar fashion. If I can hook this up correctly(correctly being operative, here) this should work.

The reverb is not mission critical. But, it would be way cool.

The whole project is going into an old Pignose 30/60 cab with the 10" speaker. I am sort of playing with the idea of some sort of fan to help dissipate the heat. This is a problem with these amps anyway. The tubes sit under the chassis and radiate all the heat upwards into the box that holds the other components. A small computer type fan and some vents should keep things nice and cool for the guys that do all the work while I rock out.

Thanks,

yug...