Solo Head 50 low output

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opauly
Bottle Rocket
Posts: 10
Joined: Thu Apr 04, 2019 12:36 am

Solo Head 50 low output

Post by opauly » Thu Apr 04, 2019 12:46 am

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?

woodbutcher65
Mark III
Posts: 193
Joined: Fri May 04, 2018 10:36 pm

Re: Solo Head 50 low output

Post by woodbutcher65 » Thu Apr 04, 2019 10:07 pm

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.

opauly
Bottle Rocket
Posts: 10
Joined: Thu Apr 04, 2019 12:36 am

Re: Solo Head 50 low output

Post by opauly » Fri Apr 12, 2019 5:11 pm

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.

Henz
Mark II
Posts: 102
Joined: Wed May 18, 2016 11:05 pm

Re: Solo Head 50 low output

Post by Henz » Tue Apr 16, 2019 1:46 am

Post deleted.
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4x12 Recto Cab w/ Eminence and V30's
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opauly
Bottle Rocket
Posts: 10
Joined: Thu Apr 04, 2019 12:36 am

Re: Solo Head 50 low output

Post by opauly » Fri May 03, 2019 11:24 pm

Any ideas?

Henz
Mark II
Posts: 102
Joined: Wed May 18, 2016 11:05 pm

Re: Solo Head 50 low output

Post by Henz » Mon May 06, 2019 10:47 am

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.
MKIIC+
2:90
4x12 Recto Cab w/ Eminence and V30's
Home made 2x12 half open cab w/ Eminence and V30's
Rocktron Patchmate, Rocktron Intellifex, TS10 Tubescreamer

McBarry
Donating Member
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Joined: Thu Jul 09, 2009 1:41 am
Location: Canberra, Australia

Re: Solo Head 50 low output

Post by McBarry » Tue May 07, 2019 3:27 am

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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