Recently I acquired a mid-to-late 70s Traynor YBA-1 Bass Master head. I’d never seen one like this before. This is the schematic that it pasted to the inside of the head.
Crazy thing was, the schematic didn’t even match the inside of the amp.
Not only was it modified, when I got it. It also seemed to have the midrange and presence control of a YBA3.
What? I’m not your dad, look it up.
Okay, like this. http://www.lynx.net/~jc/721005_YBA3.gif
Well, it sounded kinda blah. Not bad… better than most modern amps… but it was still a bit meh, and it was a perfect candidate for a few simple tweaks. Or in my case, a rude-ass rock machine.
The early Traynors were basically copies of Tweed Bassman amps with a few of the changes that Marshall made when THEY copied the tweed Bassman. The Marshall 2203/2204 circuit (most popularly known as the JCM 800 or JMP MkII) is roughly that same amp with the bright and normal channels cascaded for more gain. I decided to mod it to be a version of the JCM 800 with a few of the JCM 800 from the tone-lizard.com website. I’d already done a few like this to my 6 watt JCM 800 “tiny teabag.”
After that I continued wiring the amp. I kinda forgot to take any more pictures. In that second picture I had just finishe cascading the first two gain stage. The cathode on gain stage one is a 2.2k resistor and .68uf cap. The second gain stage has a 10k resistor. These values are both pretty close to JCM 800.
The one thing I did change was the series resistance in between gain stages. The JCM 800 has 470k resistor jumpers by a 470 pf cap in line before the 1M gain knob. I used a 100k resistor with a 500k pot, no cap. It keeps it not so horribly bright.
From there it went pretty easily. Instead of the 470k/470k voltage divider, I used a 500k pot. I’m hoping the lower overall value will take the high frequency down a bit more. Following that I restored the tone stack to the bassman/plexi setup, but using the existing component values from the Traynor, which were a .1uf bass cap, and a 1000pf treble cap. The Bassman values are .022uf and 500pf. I think I’ll keep the .1uf, but I’ll try a 500pf instead of the 1000pf.
Siince I removed the weird mid/presence, and the presence wasn’t part of the negative feedback loop, I just left the presence out. The old presence knob became the master volume.
So far, the amp rips. It just wants to cut off the heads of mythical beasts. Look our minotaurs! Next up is to check the phase inverter values. They seemed a bit low. Plus I wanted to play with the values of the feedback resistor, see if I liked it better with some other value. Oh, and I need a 2-12 cabinet.
Thanks Pete Traynor! Thanks Canada! Thanks friends of the experimental fist!