Guitfiddle
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- Nov 27, 2011
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Just picked up.
Fully loaded simul-class EV 12L combo.
86xx serial number.
"JC 11-81" top inside edge of chassis.
RP-9B pre-amp board.
x100 power tranformer
Under power cord small case "rl"? "rb"? "ml"? Can't really make it out. I'll search some images.
"LJ 2/11/82" under chassis.
"HRGS" both sides of chassis.
Anyhow, thought I would ask a couple of questions here before I call MB on Monday. I need to call anyway because the EQ sliders are all broken off but still work. Probably ship the chassis for service and updates, effects loop mod?, etc. We'll see.
First the sound. Right now it doesn't sound so good. The cleans has no low note clarity; sort of blurry and not piano-like. The filter caps are getting ready to explode; ends cracking and almost pushing stuff out. All 30uf's test at 50uf. Amp has been dormant for years. This part I understand.
The reverb on "10" is almost non-existent. Pan is good, as are all connections. I traced the circuit and and do not see V4, the 12at7 driver, paralleled! This would account for the weak reverb. The blue hot wire goes to V4b plate, plate to tube cathode .001, and unbypassed 1K cathode resistor. That's the correct values for the IIb. But the plate, grid, and cathode are not paralleled. The whole circuit seems to match the IIB until I get to this area. This one has me baffled and I build simple tweed/Marshall/blkface tube amps. I'm a master level guitar tech but not master amp tech.
Also, the black marker tube array on bottom of chassis from V1-V4 is ax7, at7, ax7, at7. V1b goes right into V2a drive circuit. That shouldn't be an at7?
Amp is all original including 4xSTR 415 6L6's. Didn't have EL34's in the outside. Doesn't look like any of the tubes have ever been removed from the sockets!
By the way this amp has been on many hit recordings in L.A. during the 80's and 90's. The seller has been a guitar repair client for 17 years.
Thank you in advance for your help.
Fully loaded simul-class EV 12L combo.
86xx serial number.
"JC 11-81" top inside edge of chassis.
RP-9B pre-amp board.
x100 power tranformer
Under power cord small case "rl"? "rb"? "ml"? Can't really make it out. I'll search some images.
"LJ 2/11/82" under chassis.
"HRGS" both sides of chassis.
Anyhow, thought I would ask a couple of questions here before I call MB on Monday. I need to call anyway because the EQ sliders are all broken off but still work. Probably ship the chassis for service and updates, effects loop mod?, etc. We'll see.
First the sound. Right now it doesn't sound so good. The cleans has no low note clarity; sort of blurry and not piano-like. The filter caps are getting ready to explode; ends cracking and almost pushing stuff out. All 30uf's test at 50uf. Amp has been dormant for years. This part I understand.
The reverb on "10" is almost non-existent. Pan is good, as are all connections. I traced the circuit and and do not see V4, the 12at7 driver, paralleled! This would account for the weak reverb. The blue hot wire goes to V4b plate, plate to tube cathode .001, and unbypassed 1K cathode resistor. That's the correct values for the IIb. But the plate, grid, and cathode are not paralleled. The whole circuit seems to match the IIB until I get to this area. This one has me baffled and I build simple tweed/Marshall/blkface tube amps. I'm a master level guitar tech but not master amp tech.
Also, the black marker tube array on bottom of chassis from V1-V4 is ax7, at7, ax7, at7. V1b goes right into V2a drive circuit. That shouldn't be an at7?
Amp is all original including 4xSTR 415 6L6's. Didn't have EL34's in the outside. Doesn't look like any of the tubes have ever been removed from the sockets!
By the way this amp has been on many hit recordings in L.A. during the 80's and 90's. The seller has been a guitar repair client for 17 years.
Thank you in advance for your help.