Kustom 72 Coupe

[CJ]

while we are waiting for parts for other projects let's tear up a red sparkle 72 Coupe that runs real hot and shares the same eq for dirt and clean channels, those are common complaints, this guy needs a volume pot and maybe we can get the bias  past -25 volts if we are lucky,

 

[CJ]

James Brown design, the Peavey Classic guy, and a funky soul singer on the side, 

lazy core pounder,

 

[CJ]

pc design

 

[CJ]

no schematic yet,  edit:  http://music-electronics-forum.com/attachments/30005d1407835258-kustom-72-coupe.pdf
makes my heart soar like an eagle! thank you internet, 

sales cut sheet,

 

[CJ]

dang, thought we had the market on this combo fixed and self bias method, (pwr tube cathode resistors and neg voltage)

no wonder it runs hot, semi class A circuit like the VOX hot box AC30 that catches on fire back in the 60's,

 

[CJ]

here is the first stage, redrawn so as to read better,

designer website>
http://www.amptweaker.com/page/About-James-1.aspx

 

[CJ]

going to verify the control board, lots of connectors, digi camera helps supply backup shots,

 

[CJ]

got some sw Vol pots in from China, dropped right in,    amp works but tone controls do not,

must be a ground, easy to find?

on a Fender Princeton Reverb they are easy to find, all chassis grounds,

see here>

 

[CJ]

not so easy on this Kustom, got pc boards, connectors, 5 different grounding schemes, denoted by circles and squares,

gotta trace everyone, remove both boards, some have a 47  ohm resistor that elevates them a bit, some go to the input jack, even the pwr supply has two or three different grounds, we have ground points by way of the controls, ground leads that clip on to the PC boards, PITA, but we will get there, don't know how they figured out what to put where, maybe a lot of trial and error,

here are a few right here, (red arrows)   

 

[CJ]

ok ripped this thing completely apart, traced all the grounds, some traces just end in space, used for reasons unknown, other connectors have a ground on one end only, confusing til you realize it is just the shield wire for the coax,

finally found a place for a pigtail lead on the chassis, circled in red, with no wire coming off of it, you can even see the ground symbol with circle stamped on the chassis next to the tab, so we just added a wire with a push on terminal from there to the tone stack-master volumes and viola, it works, sounds great, even got an email from Bob Jones, who designed this thing, he has one himself and also had to replace some of the pots,  so nightmare over, next amp is gonna be an Epiphone Galaxy 25,