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I got a free, broken Silvertone 1482.

I fired it up, and it instantly blew a fuse.

So, I took out all the tubes, put in a new fuse, turned it on, and the fuse blew insantly again.

So, the filter caps were't seeing any power. Basically the only parts getting power were the transformer, the leads going from the transformer secondaries to the rectifier socket, and the heater windings going from tube socket to tube socket.

My next step is to disconnect all the wires coming out of the transformer, appy power and see if the fuse blows. If it does , that would mean the issue HAS to be the transformer, right?

Cheers!
Ben Adrian

This happened to me once with a different brand of amp. Someone replaced the fuse holder and everything was fine. I think I got lucky though.

Did you look here?
http://www.geofex.com/ampdbug/ampdebug.htm

zack wrote:Did you look here?
http://www.geofex.com/ampdbug/ampdebug.htm

Yes I did. I ran some of the tests, and it seems like the PT is fine, but i can't be 100% certain because all of the tests only so definite failure, not definite functionality.

Also, no online sites I've found deal with what still happens if you pull all the tubes. They spend a lot of time talking about hunting down bad tubes or filter caps, but I can't find anything on basically stripping your amp down to wall plug, power switch, fuse holder, and power transformer and STILL having drastic problems.

Cheers!
Ben Adrian

Without seeing the amp it's hard to say, but it sounds like you're on the right track.

If you have a few minutes and some spare parts, build a dim bulb tester, it's handy as hell for diagnosing this kind of thing. (the one on that website has a switch; you don't really need it - just an outlet and a light socket) It will let you test voltages without burning anything up - use a low wattage bulb since you know you have a short.

Try disconnecting the heater wiring first - since it runs all through the amp in parallel it could be shorted anywhere.

Is there a capacitor to ground on the primary side of the transformer? If so it could be shorted.

I hate to even ask, but are you sure the fuses are the right value? Not that any fuse should blow with no tubes in the amp...

Good luck, let us know what you find out.

-tim

even without a rectifier tube in there, it's blowing fuses? my guess would be the rectifier tube socket needs replacing, like maybe it arc'd and now has enough residual carbon that it's always gonna arc. you would see visible charring on the socket, though, and a mini lightning bolt when the fuse blows, right?

I don't understand how you had time to find that the rectifier socket was seeing power if it was instantly blowing fuses.

before you unsolder all the leads coming off the PT, you can (with no power applied) measure the resistances of the PT secondary. for the 6V heater, 5V heater, and high voltage supply, each pair of wires should be non-zero. any that are center tapped should be non-zero from the center tap to ground, and also each half should be roughly the same.

another guess for me would be that the 5V winding or 6V winding are shorted from someone putting in tubes that draw more heater current than it can handle, like EL34's in an amp that can barely handle 6V6's, or a 5U4 rectifier in an amp designed for a GZ34.

measure the resistances of the PT secondary and check for signs of arcing on the rectifier socket. I would expect one of those tests to likely expose the problem.

i love your amp posts scott!

Im with you r0ck1r0ck2

scott wrote:even without a rectifier tube in there, it's blowing fuses? my guess would be the rectifier tube socket needs replacing, like maybe it arc'd and now has enough residual carbon that it's always gonna arc. you would see visible charring on the socket, though, and a mini lightning bolt when the fuse blows, right?

I don't see charring on the socket. BTW, this uses a 6x4 rectifier, which has a 6.3v heater, not the normal 5v of most tube amps.

scott wrote:I don't understand how you had time to find that the rectifier socket was seeing power if it was instantly blowing fuses.

That was sloppy writing on my part. Instead of seeing, it sould have said "the only placed power could possibly get to."

scott wrote:before you unsolder all the leads coming off the PT, you can (with no power applied) measure the resistances of the PT secondary. for the 6V heater, 5V heater, and high voltage supply, each pair of wires should be non-zero. any that are center tapped should be non-zero from the center tap to ground, and also each half should be roughly the same.

How far from non-zero should it be. I measured those the other night, and I think the resistance measured about 10 - 20 ohms, which seems low to me, but wasn't technically a short.

scott wrote:another guess for me would be that the 5V winding or 6V winding are shorted from someone putting in tubes that draw more heater current than it can handle, like EL34's in an amp that can barely handle 6V6's, or a 5U4 rectifier in an amp designed for a GZ34.

measure the resistances of the PT secondary and check for signs of arcing on the rectifier socket.

The amp did come with 6L6s. My hunch says the PT is friend from overstressing. I'll double check the rectifier socket.

Ben Adrian

This happened to me on a Roland JC-200. Someone had wired a transformer in backwards. I was surprised the amp even worked.

...and as a side note, the JC-200 is one big, heavy, ugly block of solid state.