This was a fun project. A 1955 Fender Bandmaster with 3 10" Jensen P10R speakers. This is the first original one I've had the pleasure of playing, I built one when I had my shop in Portland and sold it soon after. If I ever need to go 'big' again, I may build another one of these for myself, this may be the candidate for what I need.
What do I like about these? They are raw and primitive. They are part of the evolution to the more refined legendary Bassman amp. They don't work nearly as well in other words. The tone controls are a bit weird and the transformer to speakers is a good mismatch! (4 ohm transformer into a 2.6 ohm load!) That's a part of the sound for better or worse. Plus, I love the size. A Bassman is just a bit too big for any of my needs.
Speaking of that mismatch, you almost never find one with the original output transformer. They simply burned out. A friend had an even more rare Brown 3x10" from the early 60's and that had it's transformer replaced just like this one. I believe only Mercury Magnetics makes a proper 2.6 ohm transformer for these. When I built one that's what I used. Great part but I was a little let down. It was a lot more iron than I expected. I think they call it the "Fat Stack" or something like that. I prefer to have a smaller part, I don't need all that clear bass! So hopefully someone out there makes a trashier part now. A great sounding amp is a mixture of excellent quality parts and frankly, crap. Too much of either direction and you lose me.
This amp belonged at one point to a rhythm guitarist who played with Muddy Waters. When it came to me I saw pictures or the insides and outsides. I could see it had Orange Drop Sprague capacitors throughout, not my favorite, and the work looked a bit sloppy.
It also had a solid state rectifier and just okay modern tubes:
Once I played it other than a bad distortion (one of the speakers had a bad voice coil) I had to wonder what could I do to improve it besides the obvious: better tubes and a proper tube rectifier.
Once I opened it I could see the Orange Drop caps weren't the icky 715 type, but old polyester. I like those. They are nice and warm. You can identify them by the black stripe on the outside foil side:
Notice the blue resistors and the 2 "Chocolate Drop" capacitors in the preamp. Those do have to go. Not acceptable parts in a Cadillac!
Those blue metal film resistors are ok for load resistors, in fact they work better and are more stable. But stable isn't what were after here, we want that extra push over the cliff into special!
The only drag with modern Carbon Composition resistors is they seldom have long enough leads. So I had to extend the 2 watt cathode follower resistor:
Tone stack complete:
I use Mojo Dijon caps as these are my favorites. I also opted for a 250pf 500V silver mica cap for the treble cap. For the phase inverter I left the Orange Drop caps intact. I like them there. The Mojo caps are more like an old cap. Nice soft edges, warm. Mixed with the polyester Orange Drops I think it's a good balance.
Next was the tone caps on the pots themselves:
These were really poorly soldered. In fact the one on the treble pot simply came off then I touched it with a chop stick! You really need to have a high quality iron to get that joint right. Don't cheap out with your economy iron! Buy a Weller already!!! Also hit the back of the pot with sandpaper and use rosin. You'll have a much easier time of it and some pots you simply can't solder on to the back without sanding or using a scratch awl!
The caps themselves here don't matter as much, they are only bleeding some signal to ground, but I replaced them anyway cause, why not? The Mojos look more like the original Astron caps so....
Now the switches. They were fine, just not a classy part in my opinion. I can't stand seeing some big ass disco switches on one of these amps. It just looks stupid!
Also on the standby switch I needed to add a .047@600V cap to ground. Not entirely necessary but it's in the schematic so:
And if you notice in the above photo the original wire had oxidized badly. I needed to replace that length with some nice cloth stuff as well. If I wanted to be all picky I'd age the wire with coffee, but who is going to see it???
Then the bias circuit and the grid stop resistors. I did add a trim pot to adjust bias:
Next the sexy part... The tubes. These amps sell for a lot of dough. Sovteks are nice, and I do like the Chinese 12AX7 tubes it was loaded with but, let's reach for the top shelf. Sovtek 5881 tubes replaced with Tung Sol made RCA!
Also that blasphemous solid state rectifier replaced with a NOS Sylvania 5U4 made the same year as me, 1968:
Those scuzzy preamp tubes are replaced with Mullard made "Phillips" branded tubes. And the first gain stage replaced with an RCA 5751. A bit less gain but that's what Fender wanted. Want faster breakup? Use a 12AX7, or....just turn the volume knob up!
Photos of the transformers:
The power transformer and choke are original. The output is from 1961. It's a proper Schumacher Bandmaster transformer.
And a nice chassis shot:
I did use a bigger (30uf @ 500V) cap in the first stage of the power supply. Personal preference. The rest are proper 16uf and an 8uf for the preamp.
So how did it turn out? Was all this work worth it? The amp did sound great but yes, it sounds better now. That extra color to the tone, and it's a more defined. Warmer. So I say yeah, it was worth it!
So if you own one of these, you know how lovely they are. One of the most unique American made amps that ever was produced. It's unusual cause Fender knew how to build an amp like no other, so why the mis match with the transformer. As the drive to produce cleaner tones and more powerful amps to achieve this ensued, I wonder what he was thinking with this one?
For those of you who don't have the dough for an original, I see Fender is making them again. They are pricey but not as pricey. My opinion? Pay someone else like myself or maybe Victoria to build you one. We'll do you better!