Solo Head 50 low output

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opauly

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Hello,

My Solo Head 50 amp has very low output, specially in Lead channel. Tubes are OK, and already tried swapping them. The overall output is very weak considering it is a 50W amp! Bias is OK (around 20mA) and already tried checking plate and cathode resistors. I am going out of ideas!

Also, the rythm gain pot is acting very weird. I replaced it (twice) with brand new pots, but the response range is acting crazy. For example, the pot around 15% provides the max loudness, and then fades out as you turn the knob upwards. The pot is OK since I tried 2 new ones, and has the same issue. It must be something ahead in the circuit.

Do you have any idea?
 
Can you safely check the plate voltages on all the tubes and screen voltages on the power tubes?

That'd give some good data to think about.
 
I checked all plate/screen voltages as you suggested and everything looks fine. The only thing I suspect is that plate voltage on V1a should be 186V but is providing 147V. Also its cathode pin 3 should provide 2V but is measuring 1V. I desoldered surrounding components and checked them and they are within the expected range. I also changed the tube and still the same.

When I switch to Lead mode, the voltages go up obviously. But I think the schematic shows voltages in Rythm mode. Do you have any idea on what could be pulling down the voltages? All supplies are OK as well.
 
Disclaimer: Please, going inside an amp can have bad consequences. I've learned the hard way. If uncertain, refer to a qualified tech. Have / can you check all resistors and caps , mainly the Orange drops and see if they measure correctly. When was it last recapped? Take your time and gently wiggle all tubes and carefully check the connections. Give a gentle tug on the lead wires. Look for bad solder connections . Check the easiest, most obvious things first. Pots, jacks... etc. . Be careful. Good luck.
 
If the circuit voltages are within 10% of spec, then chase a signal through and see where it fades excessively.
But it does sound like it's time for experienced eyes/hands to look inside and get U a diagnosis..
 

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