I bought an old, non-functioning Precision Electronics S-35 PA as a guitar/bass conversion project. I was hoping it would be very similar to the Bogen CHB-35B. Thus far I've had a ton of fun on the project and learned a lot about electronics and tube amps (before we go further, yes, I'm discharging the things that can kill me before I go poking around-- just wanted to get that out of the way). In the future I'd really like to do more of this tinkering. Super fun. But I digress.
I've all ready got the amp up and running. I changed the input/output jacks over to 1/4" and replaced the rectifier, replaced the phase inverter tube, installed a three prong socket, removed the record-playery nonsense, removed most of the feedback circuit, and replaced the filter capacitors. It works fine now and produces a clean sound, but it's a bit bland, a bit mid-range heavy, and impossible to push into overdrive.
So I wanted to get more of a guitar-friendly sound out of it. I know from what I've read that having the master volume placed so early in the circuit isn't good... I've tried placing it after the EQ, but I get a LOT of hum... so that's no good. I'm very interested in changing the tone-stack over to the one pictured lower, removing some of the capacitors on the input side, and placing the master volume lower.
So I've discovered these two threads by a member of this forum; one where the poster tries and modifies the existing circuit and one where he (successfully) re-wires it entirely. I'm more interested in keeping the amp closer to stock.
Posts:
http://www.diyaudio.com/forums/tubes-valves/113079-precision-pa-conversion-help-needed.html
http://www.diyaudio.com/forums/tubes-valves/113271-7868-amp-sounds-good-but-low-volume.html
I wanted to ask to see if this schematic he proposes is usable-- like I said, if I move anything around, I tend to get his results... quiet, scratchy distortion. I'm thinking his problem was a bad PI tube since his amp was nonfunctional to start with... my amp is working but my problem is a lack of knowledge.
So without further ado, would this work? Thanks so much for your guys' help. I've learned a ton just by lurking around on the forum.
Thanks.
An externally hosted image should be here but it was not working when we last tested it.
This is what I'm running currently:
An externally hosted image should be here but it was not working when we last tested it.
Just a bump before I tear out the 6EU7's and put in 12AX7's to make this: Just curious is that first schematic would work or would result in the weird, scratchy distortion.
Thanks,
Thanks,
An externally hosted image should be here but it was not working when we last tested it.
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