crackle and pop, volume loss?

60jbass91 · #1 01-12-2011, 08:13 AM

I have an all original soundcity lb200, even has the old GEC tubes in from 1970. I switched it on the other day and after about ten minutes it halfed its volume, and started to crackle and pop. Any idea why?

craig.p · #2 01-12-2011, 08:33 AM

"All original" means the electrolytic caps are forty years old and may have dried out. So, I'd take the thing to a tech for a re-cap and a general check-up (tubes still ok, biasing still ok, and so on).

60jbass91 · #3 01-12-2011, 08:39 AM

it had been rewired for some time as a pa amp, so the tech just sorted it for me for 150 quid to "get it running". he said the tubes were fine, but some components would need replacing ect. If i wanted to get the whole thing back up to scratch he says it would be another 150 quid. could the caps be the only problem?

craig.p · #4 01-12-2011, 08:50 AM

Yes, caps could be the only problem. Could also have tube sockets with loose and/or oxidized pin receptacles. The components he said need replacing are probably the caps, unless he already did that as ~~past~~ part of his "getting it running." Do you have a detailed list of what he did last time?

60jbass91 · #5 01-12-2011, 08:53 AM

yeah he didnt replace no caps

craig.p · #6 01-12-2011, 09:03 AM

Ok, that's good news then, because that means there's probably nothing lurking, if you know what I mean. Have him do just the caps and see if that fixes the problem. Maybe a final check on the biasing, too, as long as he's in there. Then, while he's working on another amp, tell him to let yours cook into a dummy load (sine wave input at a reasonable frequency) at about half power just to see if he can reproduce the problem you're seeing.

60jbass91 · #7 01-12-2011, 09:15 AM

cheers pal, he already checked the bias though. i will let you know the out come