Power Transformer died

[Benjamin Ruffin]

I am reworking a 68ish Bandmaster into something Tweed. The PT was dying during the initial build and was causing some wierd noises. I thought I had just connected something incorrectly and that was causing all the weirdness. Could there be any other ill effects to the amp's circuit? I have no heaters/pilot or any secondary power at all so the PT is gone. It is original, can the PT be repaired? Just wondering.

[loudthud]

Is there continunity on any of the windings? In rare cases it is possible to repair a transformer but then it becomes a safety issue if it has been overheated. A rewind will cost more than a replacement in most cases. Be sure to check the bolt spacing before purchasing a replacement.

[Wittgenstein]

It is original, can the PT be repaired? Just wondering.

This thread by R.G. is a great place to start.

http://music-electronics-forum.com/t26848/

[Chuck H]

If "The PT was dying during the initial build and was causing some wierd noises." that should have been corrected right away. If it was hooked up incorrectly to where it causes wierd noises this would almost certainly cause other problems too. Like incorrect plate voltages and excessive dissapation in other components. Try not to take offense, but if you weren't sure if it was hooked up properly and you had reason to suspect that it might not be you really shouldn't have proceeded without positively diagnosing the issue all the way to it's solution. Especially since the PT and power supply rail are at the heart of any build. How can you possibly go forward without having that circuit correct? It's a costly and dangerous thing to power up repeatedly ignoring a notion like "I thought I had just connected something incorrectly and that was causing all the weirdness." Discontinue this practice and build mentality for your own safety. When dealing with anything potentially costly or dangerous there are two rules I always apply. First is :When in doubt, don't. Until your no longer in doubt. And second is: Understand the nature of what your dealing with. Doing things rote leaves you with no ability to recognize the symptoms of trouble. If you understood tube amplifiers you would have known there was no reason at all to power the amp up other than diagnosis of the power supply problems until the power supply problems were resolved. Whether it was a build error or not this still applies.

[Benjamin Ruffin]

Thanks all for your time and replies. I have decided to go with a new pt as this one is oem. Chuck, I read you loud and clear. I was sure the pt was connected properly as I never changed the wiring from factory. While I am not new to tube electronics (studying for years now) my hands on abilities are getting better all the time. I have a healthy fear and understanding of how dangerous large caps are and never work on an amp until I've discharged them through a resistor to ground. My question was a little cloudy, I'm sure. I doubt that it would be worth the time to try to rehab this pt, no big deal. I had just finished reworking the old ab763 circuit to a tweed/Marshall setup only to hit the power switch and...nothing. Very simple circuit with 1st stage-vol-2nd stage-CF-TS-LTP. My plan is simply to get each individual gain stage to clip a little bit so as the guitar signal gets hotter the amp will distort accordingly. I used the old tagboard and the chassis is the same. I have an extra 9 pin socket since I removed the vibrato portion of the original circuit. I would like any advice you may have about a use for the spare tube socket but it's not that important. I figure adding another pair of gain stages would be overkill. I can only chalk up the pt failure to age as I didn't do anything outlandish in the circuit. I like simple. I learn more every time I visit these pages and became a member yesterday. I have been dropping by to read these threads for some time now. I appreciate learning from experience as I feel that tube electronics is a dying art.

[Chuck H]

Whew... Good. I couldn't be sure from your first post, but after reading it, it's good to know you have the experince to manage safety issues and understand the risks. A new PT is in order then. On the up side, it's not in the BF collectability bracket so no huge losses there.

As for the spare tube... It really depends on what your after. For more and better OD tone you could add a gain stage to the end of the preamp ala Trainwreck style. This still leaves a triode unused. Or you could add a cathode follower to the output of each side of the PI. This would virtually eliminate crossover distortion and improve the power tube clipping allowing you to crank the amp more with better results. If you need volume control on the OD tone you could build an early Boogie type circuit with the extra two triodes and add a master volume. All very effective mods on old Fender amps depending on your goals.

Or, if your more into clean tones you could use the extra tube to add a reverb circuit and surfs up.

[Benjamin Ruffin]

I like the idea of a CF after the PI. Never heard of that. I will look into that. Low impedance to the grids of the 6L6's would be interesting. Have you ever
performed this type of setup? So this would be a LTP into another gain stage, right?

[Benjamin Ruffin]

You really got my gears turning. I'm trying to configure this in my mind. Anyway, awesome idea. I don't have much use for verb, as this was a non-verb amp to begin with, I'm looking for raw attitude. If you have anything drawn out for the CF after PI or a link somewhere, lemme know. Until then, I will be using my imagination.