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Peavey Tmax-Where to start?

Started by Just Mike, May 23, 2021, 08:19:35 AM

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Just Mike

When I power it up I just get a hum thru a speaker. I've built and repaired countless tube amps, but I'm going to need some guidance with this one. Where do I start troubleshooting this? I assume the power rails and output devices are the first place?

tonyharker

#1
The Peavey T-max appears to be hybrid with a Solid State power amplifier.  If it's a loud humm not affected by the volume control, disconnect the speaker immediately or it will be destroyed, and check for DC on the output terminals. If DC is present more than a few millivolts, then it is likely one or more output devices haxe expired.  You will need a schematic diagram and a conversion table for the proprietary codes Peavy use for their semiconductors.
Tony

(edited to correct typo)

Just Mike

Thanks Tony. I got a schematic and the first thing I did was pull and test the output transistors. One of the PNPs is shorted. I soldered the rest back in. Can I now test for voltages with no speaker plugged in? There are no blown fuses.



Jazz P Bass

#3
If nothing else shows as shorted after removing the bad PNP transistor, it is ok to power up the amp to check it further.
At this point do not connect a load.
And with one transistor missing, do not run the amp output to full power with a load.

Just Mike

All looks good, I have the fan operating, front panel LED's are on and front panel ch. switching buttons work. I just ordered the output device. Should be good to go, eh?

tonyharker

Often when an output device goes short it can affect the driver transistor in this case the 15031. Dont remove it just keep an eye on it when youve replaced the faulty output. BTW here's a link to a Peavey transistor list of equivalents. http://matthieu.benoit.free.fr/cross/competitive/Peavey_Transistor_Cross.pdf