Issue with my Peavey Classic 50/50 power amp Left & Right Channel

[dlezmy]

I have an issue with my Peavey Classic 50/50 power amp Left & Right Channel.
The channel 2 is about half the power compared to channel 1.
I'm using 2 great Electrovoice EVM-12L speakers (8 ohms, in stereo mode & both in the same cabinets)
I have just installed a new set of tubes and that didn't do the trick. :x
The circuitry inside looks all clean, nothing seems burnt.
I have a feeling the power supply section maybe faulty. But I maybe wrong.
I have just received the schematics thanks to Peavey, who sent them to my request.

Any helpful hints on how to diagnose the problem myself, would greatly be appreciated.

[Enzo]

SInce the two speakers are the same, we can swap them. Is channel 2 lower no matter which speaker is connected?

And then the other way. Set both controls the same, and exchange the two input cables. Is channel 2 always lower no matter which source cable is plugged into it? If the problem moves with the input cable then the trouble is in the source.

I doubt it is the power supply, since there is only one power supply and it feeds both channels. The only split is the standby switches, which feed the power tube screens. But if the bad channel switch was bad, you'd likely get no sound at all.

Here is where I am placing my bet: the small tubes. There are four small tubes. There is a 12AX7 and a 12AT7 for each channel. With the controls in front, left to right they should be 12AX7, 12AT7, 12AX7, 12AT7. Make sure you have two of each type, and verify the correct type in each of the four sockets.

Failing that, then verify screen B+ on the screen pins of all four power tubes in the channel. And verify plate voltage as well on them. No short cuts, all four. And then for each 12AT7 look for B+ on pins 1 and 6, and a goodly DC voltage on pins 3 and 8. I don;t know, maybe 150 volts or more? Not zero, is what I want to see.

[gbsnman]

Peavey Classic 50/50 Channel Problem

I am by no means an expert but I had a similar problem with my Classic 50/50.

Take the top cover off and check the ribbon cables where they connect to the power tube boards. If there has been heat build up it can melt these cables and they are so close to the top cover it can cause a ground problem.