Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: AlNewman on February 13, 2023, 09:59:35 am

Title: Fender bassman sp3100
Post by: AlNewman on February 13, 2023, 09:59:35 am

Hi, I picked up a small solid state head from the early 70's and can't find very much information on it.  It is sort of working, very distorted and quiet.  I'm wondering if anybody happens to have a schematic for it?  I found one link on another forum, but it seems to be broken. 

I ordered new filter caps to start there, there are some voltages marked on the board and the actual voltages are a fair bit higher then what is marked.  Hopefully just getting the power at proper levels will solve the problem.  I'm not familiar at all with transistors, and not having a drawing isn't making it any easier so any help is appreciated.

Thanks

Title: Re: Fender bassman sp3100
Post by: AlNewman on April 02, 2023, 09:00:03 pm

So I found a schematic a few weeks ago, searched solid state bassman, and an old thread turned up.  It was labelled something like 70's fender solid state amps. 

I got digging and there were a few things that had went.  One was R8, a fusible 100 Ohm resistor, another was I had to reattach new legs to FL1, which seems like some sort of proprietary resistor/capacitor combo, which I guess could be rebuilt if necessary, but I luckily didn't have to. 

So I replaced all the electrolytics, cleaned up the controls, adjusted the trim pots to specifications on the schematic, and it seems to perform like a 100w solid state amp.

It would probably make a decent pedal platform, even though when it was built there were no such things as pedals.  There's lots of tone options and functions to adjust, even if there is next to no natural break up when the volume is increased.  I am pretty happy with the fact that it is very serviceable even when parts go south.  Also, even when fender put out a black sheep, they still released documentation to go with it.

Just an update, schematic attached.