Bogen CHB-50 Rebuild

[physics]

Ok, I ran out of time to do much more of anything with the amp before leaving town. The last two things I did after posting here was wiring up the pilot light, and rearranging a couple connections so that immediately after coming into the amp the line's hot lead goes direct to the line fuse and from there to the power switch. Previously, it went to the power switch and then the fuse, and it is my understanding that the fuse should be the absolute first thing. After that, I handed it off to my friend for play-testing and to use while I'm out of town. When I get back I'll check his notes, my notes, and start trying to fix the issues mentioned here and any others he finds.



Part of the hand-off involved renting out a rehearsal studio for a few hours to crank the amp (with hearing protection used by those who cared, myself included) and a few other amps I brought to see how they sound. Some conclusions from the max-volume testing:

• The Bogen sounds fantastic through my detuned 2x12 and has a sizeable sonic footprint. Given I didn't do anything to really shape the sound, this seems like quite the happy accident. I just rebuilt the power supply with new parts and galactic grounding, installed a low-impedance adjustable bias supply, and paralleled the mic inputs. Technically I also added some capacitance to the plate supply node, but I don't see how that would significantly impact the sound. I have some room recordings with the PZM I mentioned in another thread, after I get the ok from my friend I'll post some clips.
  
• The high-frequency oscillation I mentioned didn't seem to be an issue in an actual playing situation. At least, I didn't notice it while my friend had his guitar near the amp, playing or otherwise. Doesn't mean it's not still an issue, but it's interesting nonetheless.
  
• Blocking distortion with the bass turned up too far is an issue. Conveniently, the first fix that comes to mind is reducing the PI to power tube coupling caps, which could take care of the oscillation at the same time. Next time I have time...
  

Anyhow, that's all I have for now!