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Help! my tube head won't turn on

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Postby spiritofjosh » September 12th, 2011, 9:40 pm

I have an Ampeg vl502 guitar head, all tube and while I was playing it it just shut off and now it won't turn back on. I checked the outer fuses and the internal and none looked blown, hell I even replaced all three just in case. Still no dice. I flip on stand by and the power lights won't come on and the tubes won't heat up. If I wiggle the power chord every so often I'll hear a pop near where the inner fuse is, but I'll check again and still no blown fuse. I'm thinking of taking it to a guitar repair shop, one with a well known good reputation but I don't want to be scalped financially. So I figured I'd come here and see if I could get possible theories on what it could be.

Anybody have possible opinions on what else it could be; output transformer maybe? I don't usually dabble in amp wiring so I'm clueless.
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Postby kent_eh » September 13th, 2011, 5:23 am

If you have no power lights and if wiggling the power cord does anything, then the problem is likely with the power cord / power connector, or associated wiring inside the amp.

It should be a relatively easy fix, if that's what it is.
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Postby spiritofjosh » September 13th, 2011, 1:16 pm

I used the power chord off an Ibanez 50 watt amp I use in my bedroom and it worked before and after I tried it with this head, so it can't be the chord itself. So like you said must be something with the power.
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Postby Jethro Rocker » January 3rd, 2012, 6:12 pm

Have you checked the power tubes? I see this is an older post but I'll give it a shot. Usually when a power (output) tube goes you'll lose a fuse too but it's worth a try. Check to see if any of the output tubes are very dark or smoky looking inside - this is assuming you haven't fixed the problem yet! :o
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Postby racetruck1 » February 11th, 2012, 8:27 pm

Really sounds like a power supply problem, could be as easy as a bad connection inside the amp or as bad as a fusible link buried inside the primary winding of the transformer.

I don't know how comfortable you are working around electrical wires but I must warn you....

THERE BE HIGH VOLTAGES INSIDE THIS AMP! AS MUCH AS 500V TO THE TUBES DEPENDING ON THE DESIGN, IF YOU ARE EVEN A LITTLE UNSURE ON DOING REPAIRS, TAKE IT TO A SHOP! THESE VOLTAGES CAN AND HAVE KILLED!

Also, just because an amp is unplugged doesn't mean that it is safe, there are capacitors inside that keep a voltage for a surprising amount of time.

If you are comfortable, look for 120v going to the transformer primary, the side of the trans. wired to the line side, if voltage is present, probably problems with the transformer. If no voltage to the trans. trace back to the cord step by step. This may show you a problem you can fix like a bad or burnt connection.

Me, I'm really stupid, I have actually fixed bad fusible links on transformers and such but I'm REALLY cheap and had to do it for a gig...... :shock:
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Postby EzraplaysEzra » April 24th, 2012, 5:12 pm

I had a guitar player I jammed with in Vermont awhile ago. He was one of those guys that had more money than brains. Anyway, he had this beauty 50watt marshall combo he used to play with, I loved it. But one day he shows up with a Deluxe RI. He tells me the night before he fired up the Marshall but got nothing but static until it died completely. So he woke up and headed down to the local music store but they weren't able to find anything wrong with the amp. So he decided to trade it for a new Deluxe. He sits down fires up the amp, plugs in and... nothing, just some static and than dead. You should have seen the look on his face. I let him barrow a cord for the day. They wouldn't let him trade the amps back though.
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