I’m building a bass amp for Robert, the bassist in my band Benesser.
It’s a Simms-Watts P.A. 200 with four KT88 in the power amp and giant transformers!
This it what it looks like original.
Here is the original schematic of the amp.
It’s very heavy, 37 kilos!
I took out most of the old components. I don’t need to use all preamp tubes since the goal is to only get one really great bass sound out of the amp and not a lot of different channels and functions.
I started with the power supply and the preamp. The preamp is based on Ampeg SVT Classic with some tweaks as a low-mid and a high-mid eq-control, where the low-mid has a peak at 250 Hz and the high-mid has a peak at 2500 Hz.
There is pretty high voltage in these monsters!
The phase inverter is basically two ”long tailed pairs” in series with 12au7 that I got from a Swedish electronic designer named Anders Hjelm. I built the bias with separate pots for each power tube so the bias can be set up seperately.
Here is the finished preamp section.
And the finished amp! I will probably publish some clips of it in the near future.