6V6 1987 build sounds like a dying fuzz (sound attached)...
Posted: Mon Mar 30, 2020 3:49 pm
Finished a new build which is essentially a 1987 circuit with 6V6s. Only change is PI 820/22K.
The (fixed) bias is fine and stable. No volume issue. B+ is around 395V on the 6V6s plates and screens.
The noise is only there when I play. Otherwise, the amp is very quiet. No hum or anything.
When I turn up the volume, the sound breaks up very early and gets into some nasty distortion... think fuzz where the transistor is biased way too cold. The note decays quickly in a bit of a choppy way...
Nodes: Pi 290V, V2 247V, V1 230V.
I think the voltages are fine:
Plates: V1 P1 140V - P6 160V / V2 P1 151V - P6 247V - V3 P1 199V - P6 188V
Also V2 P8 151V, V3 P2/7 28V - P3/8 53V
Heater voltage is good on all tubes.
So far I'm 99% sure:
-Not a component value error (triple checked everything, including measurements)
-Not something wired incorrectly. (traced everything)
-Not a continuity issue (every single connections, including grounds)
-Not DC leaking coupling cap.
-Not the tubes
-Not an external factor (guitar, speaker, cables).
I inspected all joints and redid a few which looked a bit suspicious.
I wiggled the all the tubes while playing, issue still present.
Chopsticked for a while. Nothing.
The only "clue" i have so far is when the presence pot is set between 8 and full a lot of the noise/decay goes away. I checked the PI/NFB (moved wires around, resoldered everything, changed coupling caps...) but it did not change anything.
Unfortunately, I do not have a scope.
Thanks for your suggestions!
The (fixed) bias is fine and stable. No volume issue. B+ is around 395V on the 6V6s plates and screens.
The noise is only there when I play. Otherwise, the amp is very quiet. No hum or anything.
When I turn up the volume, the sound breaks up very early and gets into some nasty distortion... think fuzz where the transistor is biased way too cold. The note decays quickly in a bit of a choppy way...
Nodes: Pi 290V, V2 247V, V1 230V.
I think the voltages are fine:
Plates: V1 P1 140V - P6 160V / V2 P1 151V - P6 247V - V3 P1 199V - P6 188V
Also V2 P8 151V, V3 P2/7 28V - P3/8 53V
Heater voltage is good on all tubes.
So far I'm 99% sure:
-Not a component value error (triple checked everything, including measurements)
-Not something wired incorrectly. (traced everything)
-Not a continuity issue (every single connections, including grounds)
-Not DC leaking coupling cap.
-Not the tubes
-Not an external factor (guitar, speaker, cables).
I inspected all joints and redid a few which looked a bit suspicious.
I wiggled the all the tubes while playing, issue still present.
Chopsticked for a while. Nothing.
The only "clue" i have so far is when the presence pot is set between 8 and full a lot of the noise/decay goes away. I checked the PI/NFB (moved wires around, resoldered everything, changed coupling caps...) but it did not change anything.
Unfortunately, I do not have a scope.
Thanks for your suggestions!