Just bought this off e-bay, hasn't come yet.
Normally they've got 2 power tubes, this one seems to have 4 of 'em. Didn't worry me at first, these old amps can vary a bit depending on when it was made, but I keep reading about this amp and and keep not finding any reference to a model with 4 6L6s. Nor have I found ANY fender amp with the specific layout of this one. It's model AB763 according to the seller, but that doesn't seem to match what's actually in it.

Was this exclusive to some brief production of them? Or a weird custom job housed in a Bandmaster head? Or what?? Should I worry?

Feeling a little stupid for not looking into this before dropping the $$$, but it never occurred to me that there'd be a totally different amp inside.

Oh, here are some pics:

Found a schematic for the AB763 circuit here, 4x6L6GC:

here

I've also found out since posting this that some of the early bandmasters came with 4 spots for 6L6s with two of them capped, and that there evidently was a popular mod to up it to 4 of 'em.

Hmmm.

Even later Bandmasters have those "plugs" over two extra holes in the chassis. And yes, the one you're looking at here was modded for 4 6L6s. It also has a bigger output transformer than stock--presumably to handle the extra power.

The AB763 circuit with 4 6L6s is for the Showman, which is otherwise essentially the same circuit as the Bandmaster.

-Tom

They used the same chassis, the Showman and the Bandmaster... my guitar player's Bandmaster has the covered up holes in his chassis too. This amp has been modified.

Hopefully it's just the extra tubes and new transformer for the added power. The new knob on the vibrato channel makes me wonder if they modded that also. Suppose I wouldn't mind, I read somewhere that it's just a square tremolo and not actually vibrato at all.

Probably just replaced the knob, though.