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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Re: amp problem posted by Ross Lipman on February 22, 2000 at 13:18:54:
O.K. Ross, now that I know what model your amp is, I feel that I can give you a worthwhile two cents' worth.
First question, are you running the original, all-metal 1614's? If you are, then they could be running away as Sans Nom suggested and you wouldn't be able to see the problem. It's easy enough to spot with glass bottles. Try to get some regular glass-bottled valves for testing. You can use any 6L6 derivatives including Sovtek 5881's which will sound better than the stock valves as well. Despite their increased filament current draw, EL34's are the best things to run in your amp.
It is common for the coupling capacitors to leak in old Mac gear. I personally don't think the 30 is collectable enough to worry about keeping stock. A nice polypropylene capacitor upgrade would do wonders for both the sound and reliability.
If your problem is not caps, there is one other possibility. That is that the amp is going into parasitic oscillation, which would explain the volume drop & distortion. If slightly higher pitched hum or other noises become audible as well, then this possibility is stronger. Parasitic Oscillation occurs in old amps when they get tired. Earth(ground) connections made via the chassis get corroded and rise in impedance, also power supplies don't isolate the various stages properly as electrolytic filter caps dry up and head south. Send me an e-mail if you want to discuss this in more eye-watering detail. Good luck.
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Follow Ups
- Re: amp problem - Joe Rosen 02:02:51 02/23/00 (0)
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