Tube Amp Output Transformer measurement

I've been troubleshooting a DIY amp that a friend of mine got it way over his head with. It is passing sound, but with really low output, and seems to die away when you try to hit it with a strong signal.

Yes, I changed the tubes.......

I have several hours of troubleshooting into this, and have decided to just unsolder all the tube, power, and pot connections, and start from scratch.

I have suspecting a bad Output Transformer since, the get-go, but I'm not sure how to test that. I measured the resistace on the primaries and secondaries, and here is what I got:

Primaries with a center tap:

Once leg to center tap: 133.9 ohms
Other leg to center tap: 136.4 ohms
Outside legs: 270.3 ohms
Secondaries have only one tap: .5 ohms

I'm not sure if the secondaries should show such low resistance, but I could be wrong.

Any input would be appreciated.

thanks.

DCR sounds right. that's not a 'change the tubes' type of problem. are sure the bias isn't way off, or that a cap is not right or connected incorrectly? Or bad solder joint? Hacking it all the way back down sounds way too brute force.


I'm hopefully wrong, but this reminds me of the guy who hacked open an A-10 transformer searching for a bad connection, and turned out the problem was an incorrect external connection.

Is it a class A amp? If so, is the output transformer gapped or at least interleaved in twos or threes (if you can see the laminations you should be able to tell)? Sounds like it might be a class A amp with an ungapped transformer which will magnetically saturate.

A P

Is it a class A amp? If so, is the output transformer gapped or at least interleaved in twos or threes (if you can see the laminations you should be able to tell)? Sounds like it might be a class A amp with an ungapped transformer which will magnetically saturate.

Click to expand...

This is a Fender Deluxe Clone (Weber Kit), so I think those amps are class B or AB?

DCR sounds right. that's not a 'change the tubes' type of problem. are sure the bias isn't way off, or that a cap is not right or connected incorrectly? Or bad solder joint? Hacking it all the way back down sounds way too brute force.

Click to expand...

Actually, I am not going to hack it down to components, just disconnect tube/pot wires. I think it may actually be a sane thing to do since my buddy have never really even used a soldering iron before this project. I could be pre-empting quite a few problems. I already found at least 2 bad solder joints.

Thanks for your input.