'68 Band Master

[clarkleach]

My business partner picked up this amp a while ago, but it sat collecting dust because "it sounds like @$$".



I finally got around to opening it up to see what lurked inside.





Oh, look! Everything is brand new!
After chasing through the circuit, I determined that it was a nicely done AB763 BandMaster circuit with a few minor exceptions:
1. A 6.8K PI tail resistor instead of the expected 22K.
2. A 1M cathode resistor on the Tremolo driver tube instead of the expected 100K.

After replacing those components the amp sounds like it's supposed to.
There was also a 0.01 uF capacitor from the plate of said tremolo driver to ground, and one or two of the oscillator capacitors had been upped in value.
Also, 1 ohm resistors were installed in series with the 6L6 cathodes to make bias measurement easier.
I chose to leave those mods in place since they are actually improvements.

One thing I will probably go back in and do is add a 100K resistor around the bias adjust pot just for insurance against the wiper losing contact.
Another detail I noticed is the cabinet. It was apparently housing a Showman of some description originally.



In conclusion, is it a genuine, certified '68 BandMaster? Nope.
Does it look and act like one? Most definitely.

Cheers

[Leo_Gnardo]

Nice find, and good work troubleshooting. Bandmaster and Showman were built in the same chassis, same size box. That's why there are two extra holes for output tubes in your Bandmaster. Wrong tag might be a factory mixup, small potatoes as problems go. When lots of orders came in, it was crunch time at the factory. Build 'em, ship 'em, woops wrong label, we're in a rush, no time to fix such details. And out the door it went.

[Enzo]

Might not even be a "mixup". Sometimes they used tube charts from other models because they ran out of the right ones. The tube line up being the same.

[dkevin]

Aren't the aftermarket transformers somewhat of a clue? I don't remember seeing Belton sockets in an amp of this vintage. It looks to me like an amp that was reconstructed from the bones of a Bandmaster. The cabinet issue may have been a factory choice. But those transformers...

[Leo_Gnardo]

Aren't the aftermarket transformers somewhat of a clue? I don't remember seeing Belton sockets in an amp of this vintage. It looks to me like an amp that was reconstructed from the bones of a Bandmaster. The cabinet issue may have been a factory choice. But those transformers...

Yes it does look thoroughly rebuilt. And whoever did it may have found a chassis here, and a box there. No matter, if it's working well that's what counts.

[clarkleach]

Aren't the aftermarket transformers somewhat of a clue? I don't remember seeing Belton sockets in an amp of this vintage. It looks to me like an amp that was reconstructed from the bones of a Bandmaster. The cabinet issue may have been a factory choice. But those transformers...

Yeah. That's pretty much what I said.

[Bob M.]

Gosh, I'd be tempted to use those two socket holes to install 6V6s (or something else?) and use the ground switch hole for switching between pairs with, maybe a bias correction/alteration pole on the switch. I have an amp I call my low powered Twin. Someone gave me a broken Twin Reverb chassis that I had some fun with. I've got 2x 6L6s and 2x 6V6s in it. I had a cabinet built for it with 1x 12" speaker. It's got a triode/pentode switch so I can go anywhere between about 12 watts to about 48 watts and it's a great sounding amp. Good for recording.

I recently read an article about a John McIntyre re-worked Bandmaster, very similar to his Bluesmaker mod for Bassman heads. During this 'down time' I just finished my own Bluesmaker and it's pretty awesome although now I'm in the tweaking phase. The premise of this amp, having a balance pot between high gain and low gain preamps is a great idea. I can't wait to do some recording with this amp.

I wish I could find a Bandmaster chassis (broken or otherwise). I have a pristine early 60s white (or yellow) tolex Bandmaster head cab that is waiting for its mate.

Bob M.