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I'm new to tube amps. I'm hoping you guys can help me. I'm working on an Epiphone So Cal 50 Tube amp. Main fuse was blown. C39 for the 12 ax7's was shorted. Wether that Cap is for B+ or heaters power, I'm not sure of that. I replaced C39 and fuse blew again. So I pulled all the fuses isolating the secondaries, and the fuse blew again. I guess its the power transformer. Usually I can smell something like that. Am I missing something? If I'm on the right track can one of you tellme? I'll get an upgrade transformer from > Mercury Magnetics < It'll cost me about $250 unless you guys know of a cheaper place. Thanks.
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Any chance you could post the schematic? -
How do I do that? I have a JPEG right hereComment
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Got it.Comment
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If you pulled all seven secondary fuses & the 3.15 SloBlo mains fuse is still popping, I would have to say the primary is shorted.
Was any work done on the primary voltage selector?Comment
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The primary is selected for 110v. It is sloppilly soldered in there though. As a matter of fact, all secondary connections are sloppy. Maybe this head is a refurb. Also somebody put a 1amp fuse in F6 where a 6.3A should go. Probably the owner, I have to ask him because If F6 blew and he didn't tell me, one of his power tubes could be bad.
About the Power supply, am I right in assuming that D5,6,7,8 rectify for the 12 AX7 heaters? And D9,10,11,12 rectify for B+? And finally the E34L heaters are fed AC?
Like I said I'm new to tube schematic symbols. Thank you for the response.Comment
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Yes, you have the power supply layout correct.Comment
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Transformers are replaced more often than they are defective because people jump to conclusions. This transformer might be shorted but you need to verify that. Do not plug it in any more, until all is in order or you might ruin an otherwise good amp. Disconnect all the wires from the primary voltage selection terminals. There are two identical primaries that are run in series or parallel depending on mains voltage. On your lowest ohms scale of your meter, measure the resistance between the wires of each winding of the primary. It is very unlikely that both would be affected so if one primary has some very low readings, the theory that the transformer is shorted is probably right. If each side has the same values, inspect carefully the primary wiring, there is a good chance it was miss-wired by someone which is why you ended up with it. A Hammond off the shelf transformer will be less than 1/2 the price and every bit as good, probably better is, as a last resort, it needs to be replaced.
If one primary is shorted, leave it disconnected and connect the remaining good primary and try it. The amp will run in the single primary but don't overtax it by running full power. That will at least let you fix the remaining problems while waiting for a transformer.Comment
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Primary is shorted. Thanks for your repliesComment
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