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My SER thread. Single Ended Revitalization.
#1
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Howdy all. New to this forum. I am trying to revitalize my SEL KT88 build that was built by a friend over 10 years ago. Working on three things at the moment...


  1. Chasing a 60hz hum issue. I get a hum even in "standby", with all tubes pulled. I assume an artificial CT is the first place to venture?
  2. Tonestack is having some real wonky interaction, so I need to gut and rewire that entire section (after 12 o clock on the treble control, it cuts ALL my bass).
  3. Lastly, I have always struggled with the texture of the distortion on the SEL. It's got a harshness that I've always had to fight a bit. I'm really more of a plexi guy, and would love to dial things back to more of a JMP 2204 sound. Any pointers are where to start first? I plan to print out out a 2204 schematic and compare and make some component changes, but if anyone would be kind enough to give a headstart on the most critical tweaks, I would greatly appreciate it!!!
Regarding #1 above. Any preferences on placement of a CT based on my build photo? The pilot light would be the easiest location. Wondering if "elevating" the CT would be better though. Would I wire resistors to pins 2 and 7 on the power tube socket? Where would be the best place to tie those into the cathode/ground given my adjustable bias resistor?

THANKS IN ADVANCE!


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#2
Update: I've not rebuilt the tonestack just yet or added an artificial CT, but I did do the James Peters mod. I like it. So far I have made the following changes.

James Peters:
- Removed C12.
-Changed R19 to 7.5K. I did not have a 5K resistor so I paralleled two 15K's. Marshall used a 10K on their cold clipper stage, so that puts me somewhere in the middle.
Others:
- I removed the cathode bypass cap on the third gain stage (ala 2204 stage 3). Removed C19 in hopes to dial back some gain and brightness.
- For fun I took the 1uf cap I pulled from c12 and paralleled it into C16. So the first stage bypass value is effectively 1.68uf. Gives a little more fatness in the lows. Just barley on the cusp of being flabby once I get past 2 o clock on the gain, but that's about as far as I push it anyways.

All together, these made a very drastic decrease in gain and fizz. At 2 o clock on the gain, its like stock gain at 11 or so, just bigger, fatter, and less harsh. Liking the direction it is heading so far. Getting me more into a 1959/2204 territory which is more my style. If I need to push it any further I can boost with a TS or KOT pedal.

Any other thoughts on sweetening things up would be welcome!
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