Moscode 300 problem

[waldtraut]

I have a Moscode 300 which lost its left channel. Could a static electric shock do this? I walked across a wool rug in rubber soled shoes to turn the amp off. Heard a rather loud pop when I hit the power switch. Turned it on again, the left channel is dead. Fuses are OK. I have a schematic, but not the skills to locate anything other than obviously bad components. Any ideas? Thanks very much.

 

[grovergardner]

That's a hybrid amp so yes, it's very possible that it would be sensitive to a static charge. Or one of the transistors could have just failed. That's a 40-year-old amp. You might still be able to find substitute parts. If you're not familiar with SS output devices I'd see if you can find someone to repair it. There are still a lot of them around so it should be fixable.

 

[grataku]

Is this amp using 2sk135/2sj50? These should have protection diodes.

Other than old caps, and thermal past drying out most other parts should be fine even after 40y. Because one channel is working you should be able to make comparative measurements with a tester.
Goes w/o saying to pay attn to the HV inside.

 

[huggygood]

 

[adason]

I have a Moscode 300 which lost its left channel. Could a static electric shock do this? I walked across a wool rug in rubber soled shoes to turn the amp off. Heard a rather loud pop when I hit the power switch. Turned it on again, the left channel is dead. Fuses are OK. I have a schematic, but not the skills to locate anything other than obviously bad components. Any ideas? Thanks very much.

Measure dc voltage on speaker output before relay.

 

[finwbu]

The designer, George Kaye, still repairs and modifies Moscode 300 .

Kaye Audio: Repairs and Upgrades of Fine Tube Electronics by George Kaye

 

[grataku]

Looks like that may be the best way to go! Would Contact him and see what he says. He may be making mods so that spike at power off is dealt with permanently.