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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: Troubleshooting a free SF Power 2...Help? posted by OwenMeany on April 9, 2006 at 17:31:06:
I sort of agree with Chris O. on this one. If you're unsure with high voltage, particularly the 500-600VDC, high current potential of a 110 watt per channel stereo tube amp can be sincerely lethal. Unfortunately for you, what is immediately wrong with your amp is probably a blown AC supply fuse or an open on/off switch. It is unlikely that it is an open on/off switch, so the fuse needs to be replaced. However, if you just replace the fuse with a suitable substitute, it will just blow again.What you really need to know is whether this amp will be cost effective for you to spend your time, even just to send it to someone else to fix. Your amp has eight 6550 output tubes, but probably seven or six of them are okay. Although tubes are expensive, the transformers are the most expensive parts of the amp. Unless you have an LCR meter, you can't easily test the output transformers. You might be able to test the power transformer. You will need to desolder the high voltage secondary from the power supply diodes, though. You see, there are probably three voltages you need to be concerned with in a tubed power amp. First is the 6.3VAC heater voltage. (Ancillary to this are any 12VDC or 6VDC regulated voltages for the heaters of the driver tubes.) Second is the negative 50-70VDC voltage that is used in a tubed power amp to inhibit the output tubes from running at full output. That's called the bias voltage. The third voltage is the high voltage or V+. That's the one that's probably causing all the trouble in your amp. Now I could be wrong about that, but because you need to find out whether the power transformer is blown and the V+ is the really dangerous part of the amp, that's the one you should probably stop from doing any mischief before you repower the amp. Now we can explain to you how to disconnect the high voltage secondary lines from the series strings of 1000V diodes, but perhaps it would be better to find out some basic information. Do you have a digital multimeter, a DMM? Do you have any experience soldering and desoldering? As an attorney, are you very litigious? As to the latter question, I'll tell you what I'll tell the judge later, "Yes sir I led the horse to water, but I was drinking at the time."
Sorry to be such a wise-ass about that, but it's in your profile so I thought it pertinent. However, if you can establish that the power transformer is not shorted, then the amp will probably be worth it to fix. You may be able to test the windings of the power transformer with a DMM, if you have one. You can also use the DMM to find out if there are any high voltages present inside the amp before you attempt to work on it. You can bleed off all the high voltages from the filter caps and make the amp safe to work on, but, again, it's a dangerous amp for anyone to work on and it's a dangerous amp for you to learn on. Unusually so. But if you wish to proceed, you might walk your question over to the Tube DIY forum. Get Mikey to try it. He'll try anything.
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- Re: Troubleshooting a free SF Power 2...Help? - corerosin 01:41:00 04/10/06 (0)
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