Mesa Rocket 44 bias circuit mod?

[moshpit903]

This thread has mentioned bad OD cap(s)..I dropped my Single Recto off last Monday to a real Mesa Tech and he was saying that he's going to look at all the OD caps and check them out,saying they can be a headache on Mesa amps,and now I read it here.
I am slowly learning that Mesas are difficult to work on ..this forum is full off good info and I have been reading all the Mesa threads and lots of the others..very informative..I hope I didn't hijack here,just saying this place is full of good info.

[lowell]

Cheap pcb boards, bad design. I had this issue in this thread from a while back. https://music-electronics-forum.com/...ht=mesa+rocket

I now have the same model amp on my bench with this exact issue. It is a different amp than the one I fixed before... which I seemed to have fixed by reducing the 120k bias resistor to 80k.

Steveward you are the man if that fixes it... I bet it will. I've fixed Mesa's before by drilling holes in the pcb to mitigate stray conductivity.

[lowell]

Lifted the anode of the bias diode, removed the 120k dropping resistor, floated the junction of the two, ran a floating wire to the 33k/15k junction. Fixed. Conductive board.

[NoelW]

I have just repaired a mesa Boogie rocket 44 with a very low bias supply . This lead to overheating valves and power transformer. The fault had developed over time and the customer was using up valves at an alarming rate .
All the components in the bias chain were perfect . The problem which was invisible to the naked eye was the PCB which had broken down and was conducting between tracks. None of this was apparent or measurable with test gear until the components were removed . The problem area being around the 1n4007 and the 120k resistor. The track from the AC supply was cut and the the diode and 120k resistor mounted externally. The resistor wa also unsuitable to handle 300+ volts ac and the 120k is now made up of 2 x 60 K resistors . The Bias chain now functions correctly -16.5 volts dc with roughly -12 volts on pin2 of the el84s and the 12-3 volts on the cathode of V1
Hope this helps someone. It took several hours to find this poor design issue. # track spacing wrong for such high voltage Ac and DC in close proximity ..
Regards Steve

Hi Steve,

I have a 50 Caliber+, with 2 x 6L6, on my bench with similar problems and a suspect circuit board in the Bias component area.
The board has been hot and is discoloured, as a witness to this. It has also had a dodgy adjustment pot added, which failed and I have removed it and the associated circuitry.

Can you tell me what you did about the Phase Inverter Bias, when you mounted the Power Tube Bias externally.