Band Master AB763 trouble

[xtian]

No dirty pins or sockets.

Problem is post-PI. (I removed the power tubes, and signal looks good and strong with no uglyness.)

Tried three sets of power tubes.

I'm going to tack in a different OT. Will be easy, have one here with long leads.

[xtian]

Yeah, I just tacked in another OT, and it works great.

Then I soldered the original one back in, just to make sure there were no cold solder joints--same terrible sound. Partially blown OT.

[Richie]

A lot of people take the bandmaster OT off, and put a 50 watt bassman transformer on them. I've seen quite a few of those.

[gldtp99]

I'd use this OT: http://www.classictone.net/40-18006.html

Great sounding unit---- has 4/8/16 ohm secondary taps----- I converted one BF Bandmaster to a Bassman type 4/8/16 ohm OT several yrs ago--- It's ok but not worth the bother and extra expense, IMO...........................gldtp99

PS--- Here's a BF Tremolux that I replaced the bad orig OT with the ClassicTone OT linked to above:

http://youtu.be/E9DT3zzplak

[Stevem]

When you have a amp with a problem that may point to a bad OT having 1 ohm current measuring resistors in each output tubes cathode is a blessing for trouble shooting.
When a output(s) tube is trying to drive a bad OT you will see the current soar when you pump signal thru the amp and get little or crappy sound out of it, and you may already have the tube(s) near red plating or into red plating and making extra hum even before driving the amp with signal. to test it.

[xtian]

Good info, Steve. Thanks.

[Rat6v6]

+1 for http://www.classictone.net/40-18006.html
I just put one in a 1966 Bandmaster myself.
It had exactly the same problems as you are describing. Horrible distortion with either channel volume > 3.

+1 for the 1 ohm resistors. Makes checking bias much easier. What I also did when I converted to a 3 prong power cord, is I removed the power from the aux socket and then used short wires to connect each tube to from pin 8 to one of the sockets. That way you can check the Bias of each tube without having to pull out tubes for bias probes.

I also had to change the PI caps as one of them was leaking DC causing one of the tubes to cut out with with signal applied. (Monitored bias voltage of each power tube while adding signal).

Also - check the Bias cap. Mine had the original 50v cap and I had -60 volts on it. I changed mine to a 100v cap.

HTH