Music Man 112 RP Guitar Amp

[CJ]

getting after a hybrid git amp with some unique features,

has a built in "Phasor" and a weird output circuit,

pair of 6CA7/EL34 tubes with a hi/lo pwr switch,

packs a punch for a one 12 combo,

gets good reviews online,

 

[CJ]

chassis

 

[CJ]

more chassis,

 

[CJ]

let's zoom in,

sockets let some folks experiment with other chips,

 

[CJ]

more chassis,

 

[CJ]

output circuit,

grids are held constant, modulation by way of the cathodes,

has lots of oscillation  caps,  clipped them out but might put them back in,
(500  pf on sec legs)

getting some not so nice crunch noise at certain gain/vol settings,

OPT could be the culprit but caps are easier than a rewind,

718 volts on the plate at the high setting!

keep your arms and legs inside the bus while it is moving,  ;D

note grounded suppressor grids sit lower than cathodes

hi/lo voltages:

plate - 478/718
screen - 236/357
grid - 24/24
cathode - 45/58

if you subtract cathode offset you only have 718-58= 660 on the plates,

problem was somebody had the speaker plugged into the ext jack,

 

[PRR]

> note grounded suppressor grids sit lower than cathodes

Thanks for pointing that out. I can analyze this contraption, but the bias always looked a bit off.... I was overlooking the negative on G3.

Traynor did similar on a few big amps (tying G3 to the negative G1 bias source).

It don't do anything magical, just shifts the curves a bit. Really just makes it hard to predict G1 bias. Old-time G-amp design was a lot of try-and-fry.

 

[Travis1000]

I used to have one of these. They sound great to my ears!