To tell the year,I just checked my ’66 Showman,AB763 chassis,Brad shows you how to do it,look for the # on the body of the transformer it should read 606 for Schumacher and the next # is the yr. last 2 #’s are the week of the yr.Good info,I always thought mine was a ’63 so I was told by the person that gave it to me?The week # was 07 preceded by a 6,so mine is a ’66,I would think.Having such a low week #?

i have a blaceface dual showman that needed to have the fuse (2.5 amp slo~blo) replaced. i had switched on and off one too many times, and it did what it was meant to do. anyway, i got a free fuse from the electronic store, and am now running my guitar through a 2~12’’ speaker cabinet.

right there with you, at last count we had 34 Dual Showman amps and even a Fender PA system. We also have 30 or 40 Fender guitars. Have some Vox and Peavey amps.

No such thing as “un-bias”. Never heard of a “preferred” circuit board either. All Showmans were fixed bias, and there is an adjustment pot inside the chassis. You never need to change the bias setting unless you want a different sound, or changing to radically different tubes. Since the bias adjustment pot is global, it’s always best practice to install “matched” pairs (or quads) of tubes. If they are not matched, you will hear a “hum” in the speakers and possibly one of the tubes will have red glowing plates, which is a serious problem. Some of the circuits used a “Balance” pot for the bias, which does not change the global setting but will correct the problem of poor matching (reduces the “hum” in the speakers). You may need a technician to tell you which one you have. The only other way to tell, without looking at the circuit, is to turn the pot one way and see if there’s rapid increase of “hum” in the speakers and two of the tubes start glowing. If so, just move the pot to where there is the least amount of “hum”. But if in one direction all 4 tubes start glowing and the other direction turns off all sound, then it’s a global pot. Blackface Band-Masters and Showmans were the same size head, so the chassis was probably swapped out. The tubes will be the same, except for 2 extra 6L6s on the output. Single Showmans have one speaker with an 8-ohm output transformer. Dual Showmans have two speakers with a 4-ohm output transformer. Neither have reverb, unless it says REVERB on the front panel, and then the head box would be taller to accommodate the spring pan.

I have a what I was told was a ’68 Showman amp with the face plate replaced with one that says Dual Showman. The label inside says Bandmaster and shows a diagram with 2 6L6s. I have 4 tubes. Also the diagram doesn’t seem to match the amount of preamp tubes that I have. I want to know what I own. Especially if I have the “preferred circuit board” I don’t have reverb so It’s not a Dual Showman right? How do I tell the year? The label is torn a bit. Also is this un-bias? Does that mean I can change tubes without having a tech adjust the bias? Any help would be tremendous. Thanks.