Re: SF Bandmaster
First off, if it is a SF, are we talking about the regular Bandmaster or the Bandmaster Reverb ('68 on on)? The BR sounds different than the regular BM. Both of them sound good, IMO, but the BR does have more thickness and sounds great for clean and dirty. After some a/b tests, I find that I like them both for clean, but for my tone I like the non-reverb model better as it's more articulate (IMO of course) for the clean tones. For the dirty tones, I prefer the Bandmaster Reverb.
The folks above are talking about transformers...the true heart of the amp, IMHO. OT=Output Transformer, PT=Power Transformer. Changing the transformer can really change the character of the amp; some folks change the transformers in the Bandmasters to get the tone closer to the more sought models/versions of Fender amps (at least I think that's why they do it).