[/quote]Nice first post!!! That would be my understanding for the mods as I have read them. Someone posted in the forum the Lead Drive mod and indicated that you need a 1M resistor AND a volume pot to make the lead drive at R292. They also indicated you needed to cut the trace to between Cap C5 and LDR2. Since I posted this response, I found this that talks about the lead drive mod with pics.
http://acapella.harmony-central.com/showthread.php?t=2223437
I also found this that talks about the Lead Master Mod.
https://www.premierguitar.com/Magazine/Issue/2008/May/Boogie_Tricks_A_Fuse_Fix.aspx
I hope someone can confirm these mods as I am very interested in performing both. Great question and welcome!!!
Mike[/quote]
Thanks for your welcome Mike. This is a great resource.
Thanks for the links too - I've joined that Harmony forum and asked one of the guys for the mesa mod schematic. I can see what they're doing but my solution is slightly different (maybe easier and can be un-done). I'l post a schematic soon for your interest & confirm if it works when done.
Likewise with the premierguitar Lead Master advice - I was planning on trying this method too. Seems the easier of the two mods.
Last week I cleaned the rotary and slider pots with Faderlube and cannot believe what difference it made to them - I can now feel the click of the slider's centre notch and everything is smoooth. Wow! They must have been filthy after 22 years of use without a clean.
I'm gonna try the amp like this before the mods so I can hear where I'm starting from. I'm hoping this dirt was the cause of the amp sounding dull and hissy over the last few years - tried new valves and had the amp serviced but made no difference.
Would seriously advise everyone to clean their pots and contacts. Anyone have experience of this? I used D5 for the contacts - what do you fellas use? I hope I'm not trying to teach grandma how to suck eggs, but such a simple thing as cleaning the pots & contacts could make an enormous difference. Feel stupid for not thinking of it before
When doing the mods I may also replace the hot wire from the input jack socket to the PCB with an OFC screened cable. May give a further cut to any noise contamination at this crucial early stage of the pre-amp. I notice recent Mesa amps have a ferrite component in this position. Could be an option. My Nomad has almost no hiss at any setting except very high gain, as all amps do.
Also may insulate any bare wires (such as those to ground) to reduce the chance of short circuits and replace the wires to/from the reverb box with OFC quality, screened cable. I'll check the reverb send/return operating voltage, but hi-fi screened cable should be ok.
Finally, I've seen amp servicing options to replace the filter capacitors, which seems to be a usual mod to old amps. I wonder if they degrade over time and it's partially this that gives old amps their 'vintage' tone? Or replacing is necessary to maintain good tone? What difference would this make to a 20 year amp. Worth doing? Any thoughts?