Champ 12 Transformer Blow

[vmazz]

OK I made a big mistake. Doing some upgrades to my amp and was rushed I ran it without the speaker Now there is just silence....SO Im pretty sure I blew my output transformer. My question to the knowledgeable members here would be. Can I just replace the OT or is there something else I might have damaged.
I know its the cardinal sin of tube amps, I just got rushed by my wife and was trying to finish what I was doing.:

[clintronics]

Just Curious

How long did you run it without a speaker?

[vmazz]

I ran it about 3 min idle. I was trying to set the bias with a new Torres bias assembly. Really dumb! My hope is I can just replace the OT, as I had thought about upgrading that anyway. When I realized later that I had skipped hooking up the speaker I hooked it all up and ran it reset the bias again. Everything looked good(all the tubes warmed up etc) but no sound coming out when hooked up to my guitar..NADA. Any help would be great

[Twist]

There's a good chance you didn't damage it unless you were actually playing your guitar with the volume up a bit. Just sitting there idling for a couple of minutes shouldn't have popped the OT. Although it's best to have the speaker load attached while adjusting idle current. I wouldn't panic yet. My experience with bad OT's is they usually produce some sound although it may be weak or distorted. If I understand right your saying it's completely silent.

[vmazz]

Hey Twist, thanks for the glimmer of hope. Yes it is totally silent. Which means now I have to troubleshoot. I did some circuit changes suggested by Ray Ivers. I lifted a trace and used the cap leg to fill in I may have shorted or something. Thanks For the Hope... Oh and I suppose there is someway to test the OT

[stokes]

With no signal going thru the amp you should be okay.Do you have a signal generator and some way of tracing the signal?

[vmazz]

well..no and no..to answer your question, but I have been thinking about making an Audio Probe.. is that what you had in mind? I am definitely looking for suggestions to troubleshoot. The first thing I was going to do was open it back up and double check all the connections. This amp also has a headphone jack I thought about trying that to. Would that tell me anything?

[Twist]

Here's a generic way to check a Champ OT. Disconnect all the OT leads. Now generate a 10 volt AC signal on the two primary taps. If it's good you should read about 0.20 volts AC on the secondary 4 ohm tap. I use an old military tube type signal generator. I'm not sure but you might be able to use a small step down 10 volt AC transformer in place of a signal generator. Double check and make sure your applying 10 volts AC because sometimes the primary of the speaker tranny can load down the signal.

[Enzo]

Idling, the amp should be OK without a speaker - nothing to generate back voltage spikes without a signal.

You got a CD player or tape deck or something? I have a shop guitar or two for testing, but on the bench when I just want to see if something works, I have a line out from my shop stereo hanging nearby. I tune to a local music station on FM, but any music will do.

If you have no test tone generator, plug some music into the amp input jack. Now then, to trace the signal through the amp, set your meter on AC volts. Unless your meter is abssolutely bottom end, it will ignore the circuit DC and just measure AC. and that AC will be the signal.

Here is a test for the meter. Set it to AC volts and hold the probes on the terminals of a 9v battery. If the reading stays at 6-12v somewhere, then the meter is not suited. But if the meter settles down to about zero volts AC after a second or two, then it will work here.

And if you are not sure if it is signal or not that you are reading, turn off the signal, or unplug it for a moment. If the AC voltage goes away when yuo do, then it was signal on the meter.

So with music applied to the input, is there AC on the output tube plate? Its grid? Plate of previous stage? etc.

[vmazz]

Thanks for the help

Thanks for all the input. I ended up not having to do much troubleshooting. I found a broken connection to v1 and redid the lifted trace with a better connection. It works. Though I have 2 mods going on it and I think I might undue one. The tone is much louder brighter but I think I need some more low end.I have the Torres tone mode and some circuit changes attributed to Ray Ivers . I think I may disconnect the Torres as it is easily done (* separate from the board). Anyways thanks to all. And I chalk this up as further learning somewhere towards dangerously competent.