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Topic: Breathing life into an old Amp. |
Rick Rienks
From:
Oregon, USA
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Posted 19 Sep 2024 4:56 pm |
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I have an old Harmony amp. It is an H303A. When I plugged it in it made a strong 60 cycle hum. I quickly shut it off. I knew what that meant - the power supply filter. It has been a long time since I last worked on amplifier circuits so I did some research. It seems things have changed since my early 60’s experience. Heck, our Navy A/C still were mostly tubes. The source of the problem is, hopefully, limited to the can containing the electrolytic capacitors. The original values were two 40 mfd and one 20 mfd, all 150v. Searching around I can find higher value, 22 mfd and 47 mfd. assuming the voltage is correct, can I expect problems with these values? I did find one vendor with a can containing two 20 mfd and two 40 mfd. I was thinking that might mount to the chassis (to retain the look) and one cap could remain idle.
Any thoughts would be appreciated. I have seen photos of this repair using current caps but no data nor source. Living in the boonies and lacking knowledgeable thoughts I am letting this restore lay idle. I would like to put the little 5watt amp in service for the sake of hearing my ‘61 Supro played through that amp. Thank you all for any insights. |
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Mike Auman
From:
North Texas, USA
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Posted 19 Sep 2024 6:25 pm
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You can go with higher capacitor values with no problem, as long as the voltage rating is at least 150V. Or if you go with the 4-pack, you can leave the 4th replacement cap idle, or put it in parallel with the B source 40 uF cap, like they did with the two A source caps. And I'm sure you remember that the polarity is important when installing electrolytic caps. Here's the schematic if it would be helpful, the power filter caps are at bottom right.
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Long-time guitar player, now wrestling with lap steel. |
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Rick Rienks
From:
Oregon, USA
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Posted 19 Sep 2024 9:58 pm Harmony H303A Schematic.
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| Hello Mike, thank you for the schematic and thoughts. Having looked at the can, I am guessing the casing may be ground and the leads should be routed as per the old ones - thus be properly rigged for polarity. I appreciate your response and will contemplate my next step, which will be to clean up my work bench/catch-all. Currently there is no room for any project. Once again I see evidence that God has a sense of humor. Best regards, Rick |
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