DIY modding 50 Caliber +. Can i do it? and how?

[seth155]

i've heard/read of a mod that adds a separate Master knob, or gain knob or something to the clean, or gain channel in order to make the two channels more independent of each other.

questions:

1. does anybody know what i'm talking about?

2. would someone who is versed in following guitar electronics diagrams (NOT schematics) be able to perform this opperation?

3. are there any diagrams available?

 

[Don]

If it's a Plus then it should already have a lead master control. I think you're talking about a lead drive control. I put them on my .22+ and I assume the procedure is similar. There used to be pics of a modified PCB available though I haven't seen them lately.

Here's a pic of the mod for a .22+. The resistor might be a different value and the number is probably different on a 50+

Here's a link to the thread that pic was from-
http://forum.grailtone.com/viewtopic.php?f=3&t=30067&start=59

Maybe someone has more specific details and pics.

 

[seth155]

this thread was looking for the same thing i'm looking for:

http://forum.grailtone.com/viewtopic.php?f=28&t=42474

unfortunately i have no clue what those answers were about

 

[seth155]

i would try to do the mod with the diagram above, but i have no idea what an LDR is, or where it would be located.
is there anybody who could give a step-by-step tutorial?

 

[Nicklotsaguitars]

Did similar to my 2203KK and JMP. It's quite an easy mod. The hardest part about it is finding space for another pot.

Find R102 on the circuitboard (near V1 and trace your way back from there. C5, R292.

Personally, and I say this in absolute kindness. If you're struggling to find that section of the circuit. It is probably better if you pay someone to do the mod for you. You could mess your amp up, you could mess yourself up.
A lot of people these days drain caps by grounding V1 pin1. The anode. Which looking at the drawing, unless I'm mistaken is where R102 connects to.
Never worked on a Mesa amp, I don't know if they work the same for sure, I wouldn't be risking it.

All the best with it mate.

 

[Chaos2k]

I'd be very interested to do this mod as well. What I'm wondering though is what the correct value for the R292 replacement and the Pot would need to be. The Caliber .22+ Lead Drive mod is specced for a C5 value of .001uf and a R292 value of 470k. Apparently this is the same only on the Caliber 50 6BQ5/EL85 model. My model is a 6L6GC and the schematic says it has a 150k Resistor in place of R292 and a C5 with .003uf.

As far as I can tell, this is a result of the different input impedence it has compared to the .22+, but I'm not sure. Has anyone done the Lead Drive Mod / Lead Gain Mod on the Caliber 50+ 6L6GC model and could provide the values to use here?

I'm not sure I fully understand the way this mod works, but my guess would be that replacing R292 with a 300k and going with a 300k Pot (probably only gonna get a 250k one) should do the trick. As far as I can tell, R292 just bleeds the signal to ground thereby attenuating it (after it has gone through the de-coupling cap C5).

I would also want to to the "Deep Pull" mod, wiring a .022uf cap in parallel to C5 with a switch. Anyone has experience with good pot value there as well?