I've been banging my head against a power amp issue for a week or two now. I'm converting an old Lowery organ amp (6V6 PP) to a JCM800-style guitar amp, and everything works beautifully until I plug in the power tubes to check for output level. One tube shows twice the output level, and at more than about 10% volume, I was getting doubling distortion. I proof-read my circuit more times than I can count, checked for bad solder joints, dropped the supply voltage by 100 volts (to get about 350 on the 6V6 plates), even tried chanting "Go, push-pull, Go!!" while standing on my head and making Walrus noises (not really). I was almost to the point of totally gutting the power amp circuit and starting over with the wiring just in case there was a hidden issue that I just wasn't seeing. Well, it turns out there WAS a hidden issue, and I didn't need to do a full tear-down to find it.
The output OPT primary winding has orange-ish colored leads and a single blue-green lead. I made the mistake of assuming the blue/green lead was the center tap. it isn't. Turns out there are actually three different colors, but age has made two look all but identical. Testing the transformer showed the error, and I've now got the center marked with some black ink, and all is now well.
Just thought I'd share in case anyone else has had the same kind of experience!
The output OPT primary winding has orange-ish colored leads and a single blue-green lead. I made the mistake of assuming the blue/green lead was the center tap. it isn't. Turns out there are actually three different colors, but age has made two look all but identical. Testing the transformer showed the error, and I've now got the center marked with some black ink, and all is now well.
Just thought I'd share in case anyone else has had the same kind of experience!
