Egnater Rebel 20 Plate V and other issues

[Pryde]

Schematic Attached

Working on this Egnater Rebel 20. It presents with sub-octave (ghost) notes, and unwanted distortion and constant low-level hum. Sounds like a fuzz-octave pedal is on playing notes anywhere. My thoughts were bad power supply caps or wonky bias perhaps.

The issue is certainly in the power amp as the pre-amp out sounds good into another amp.

Checking plate voltage and bias current shows a problem: All power tube plates are reading ~300vDC. Based on other threads I think they should be ~360vDC? Bias current for 6v6s only -9v m/a with trim pot maxed, EL84's get -18 m/a with trim pot maxed (per tube usuing bias probe).

Getting 288vAC at QC104/105, then 308vDC on D101 and D102 rectifier diodes, then 308vDC at QC102, then 301vDC at B+3, then 262 B+4.

Not sure about these voltages? The schematic doesn't indicate what should be happening. Any thoughts? thanks for the help.

[Pryde]

Forgot to add that I am indeed seeing 60vAC on that QC101 connector. THe rectifier diodes are not open. Is this indicating possibly C126 or C127 is faulty?

[The Dude]

I would check for ripple on the output B+ line. Your plate voltage seems low, possibly caused by poor filtering.

[The Dude]

Sorry,......simulpost!

If you have 60VAC at QC101, I would suspect C127 faulty.

[Pryde]

Sorry,......simulpost!

If you have 60VAC at QC101, I would suspect C127 faulty.

OK thanks. So this would then drop my B+, bias, etc voltage to that degree? (i.e. apprx 60vDC). I am hoping that replacing the filter caps will get all this back into proper voltage range.

Also I am getting -65vDC coming out of that bias diode (D203). Not sure if that is correct?

Also need about 30mm case length for the 100uf and mouser is out. They do have a 120uf in proper size though.

[The Dude]

Your bias supply is a separate supply, so that won't change. Higher B+ will make the tubes conduct more and you should then be able to adjust the bias in range. 120UF should be fine.