Musicman rehab

[Mars Amp Repair]

Marc,
Thanx for the lead on the BrownDog adaptors. I'd never heard of them. I was just rewiring with sockets around the RC4136 IC's in the older Ampegs. glen

[Marc]

project update

This amp was such a bargain! thank goodness I'm only into it for a stupid amount of time and less than $100 in parts....

The browndog adapters are working fine, yea!
The tremolo works only on high power?!?
I cut it to low and the voltage drops to about +/- 10 and it stops oscillating.
At high power it has about 15V +/- and seems to be working fine.
Tried a different oscillator transistor and no difference.
It's weird how this amp changes the primary on the OT instead of the secondary. so the filament also drops to about 4.5V from 6.5v.

Has anyone seen this before?
I'm getting tired (bored) with tinkering on this amp. It will never be a collector's piece but it would be nice to be a player's piece!

Marc

[Marc]

Is it possible that the voltage drop is due to the higher current demands of the NE5534 opamps?

I'll try subbing the old opamps back in one at a time and see if that affects the voltage.....more later!

Marc

[Marc]

And the answer is yes!
the NE 5534 opamps loaded down the supply enough to turn off the tremolo in low power.
I put the original opamps back in one by one and after just three the voltage was back up to +/- 15 an the trem is not working.
Not to try out these Sano branded speakers that came in this beasty......
Anybody need some Brown Dog adapters with sockets installed?

Marc

[KM22]

Marc,

Thanks for all of the great reports on your MM amp rework. I have an HD 130 that I will dig into at some point to restore and will certianly refer to your experiences.

Did you ever share your 6GM5 tube amp project on the ME forum - It sounds like someting I'd like to try!

Thanks,
--Kurt

update....after setting this MM aside for a while and building a smokin' amp with 6GM5 power tubes and a champ clone, it's time to get this MM back on the bench again.
I've ordered the browndog adapters and new opamps. I'm starting with NE5534's and going from there.... My reasoning is that is if the caps were bad there's a good chance the opamps are too.
So for about $30 I'll find out in a week or so.....and report in.

Marc

[drewl]

Every once in a while I'll find a bad opamp on a MM, most of the time its the solid state driver phase inverter and the 16volt zener diodes for the opamp power supplies.
They are usually half burnt and at least need to be resoldered.
Better to just replace them.

I have one with some hum in the preamp.
Seems normal to me, but the customer thinks it's excessive.