King Nothing - Oscillating

[drew.spriggs]

Howdy,

Built a King Nothing. Everything works fine, voltages are spot on (254v on the plate resistors, and 29v heading into the J201), but there's significant amounts of oscillation that decreases as the gain is turned up. Low switch has no impact on the noise, but the left position of the mode decreases the range where it oscillates from about 1-9 to 1-3 (assuming each tick is about 30 degrees of rotation).

I've tried multiple power supplies, from isolated DC bricks, to cheap SMPS to an old unregulated power supply I've got around (all capable of +500ma), and no difference. Tried multiple guitars, multiple leads, etc and there is no difference.

Tube is a brand new Shuguang 7021 (confirmed to be good), J201 is a onSemi MMBFJ201 on a SOT23>T092 adapter board.

Thoughts?

 

[drew.spriggs]

Ok, tried a few things:

1. Decreased R5 (plate resistor on second stage) from 220k to 100k. No change
2. Tried an old EHX 12AX7B I had spare from my amp. No change.
3. Tested a 100pf cap in parallel with R13/R14 for RF suppression coming in, as well as across D/G of the J201 (in case it's oscillating there). No change.

I've also noticed that when it's oscillating, it is MORE noticeable in bypass (didn't notice that originally).

I've confirmed every component is correct, and there are no sketchy solder joints.

Semiconductors:

1. TE NE555P
2. Central 2N3904
3. Vishay IRFB17N50 (have used on previous builds and works perfectly).

 

[Smrtokvitek]

By oscillation, do you mean high-pitch squeak overtaking the overall sound or just a background "noise"?
It would be nice to share a picture of your build.

 

[drew.spriggs]

By oscillation, do you mean high-pitch squeak overtaking the overall sound or just a background "noise"?
It would be nice to share a picture of your build.

Squeal significantly louder than signal levels