Peavey Ultra plus 120 power tubes not coming on

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jatspic05
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Peavey Ultra plus 120 power tubes not coming on

Post by jatspic05 » Sun Nov 20, 2022 7:43 pm

Hi,
I have a Peavey ultra plus 120 that was working fine. The next day I turned it on as usual and I have no sound and the power tubes are not glowing/coming on. I measured voltage at the power switch, across the fuses and up to the power section board. I have 525 volts at the board and on all the pin 3 locations. I checked the transformer connector on the other end of the board and there is 525 volts. I checked continuity on all of the power tube pins sockets to the board and there is continuity. I checked the R200,201,204 and 205, I have 96 ohms. I checked ohms on the transformer plug, on one half I have 70 ohms on the other half I have 40 ohms. I have also changed the power tubes. I connected my eurotube pro one tube socket on the tubes and I get nothing, the pro one doesn't turn on? Anyone have any other solutions??

rogue777
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by rogue777 » Sun Nov 20, 2022 9:36 pm

Did you check the filament fuse F1 10A fast blow?

jatspic05
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by jatspic05 » Mon Nov 21, 2022 4:43 am

Yes, looks ok. There is power across the fuse. I ordered a new one just to swap.

rogue777
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by rogue777 » Mon Nov 21, 2022 6:37 pm

Hi jatspic, it’s a good thing you ordered another fuse.
The best way to measure a fuse is to take it out of the circuit and measure ohms thru it on the bench.
If possible try to measure the 6.3 vac at any 6l6 tube from pins 2 to 7 with your dvm?

jatspic05
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by jatspic05 » Mon Nov 21, 2022 9:05 pm

Tomorrow I will check the voltage. I have also checked the two 22 ohm resistors R301,302 that go to the filament. They measured 11 ohms, I assume because they are in parallel. I also checked diodes CR 21,22,23,24. 21 and 22 bleed some. 23 and 24 check out as a diode should. I did just pull the fuse as you said and I show OL and there is no continuity through the fuse, I guess that means it must be bad! I sure hope so. The next question is why did the fuse go out? I will try the new fuse when I get it and report back. Thank you for your help! have a great night.

rogue777
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by rogue777 » Tue Nov 22, 2022 12:52 am

I can't find R301,302, i'll look for them. The schematic I'm looking at has R93,94 each 100 ohm on the filaments to create an AC center grnd. Maybe were looking at different schematics, it happens. Fantastic that you found some other diodes bad too. You'll get it fixed.

I think when you get that new fuse in, you'll be up and running, or at least were you were before.
Fuse failure: I'm guessing one of the 6l6 tubes arced or shorted between the filament and the cathode, popped the fuse.
So you could have a bad output tube.

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guitarman59
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Re: Peavey Ultra plus 120 power tubes not coming on

Post by guitarman59 » Mon Dec 12, 2022 12:05 pm

jatspic05 wrote:
Mon Nov 21, 2022 4:43 am
Yes, looks ok. There is power across the fuse. I ordered a new one just to swap.
A voltage reading across a fuse means its open or blown in my experience. Continuity test out of circuit is still the best way to test.
Glad you found it.


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