• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Thorens PR24

Does anyone here know this amp? I have one, and last evening I tried it. It did sound pretty nice for a while, then suddenly it faded away in both channels at the same time. No more sound since then :(
When I opened it the two solderings (at the arrowheads in the attached picture) had loosened completely. I did solder them back, but to no help. Still no sound.
If anyone have a service manual/schematics for this amp, or know where to find one, it would be to great help. I have searched the net, but can only find schematics for Thorens AZ 25, the successor of PR 24, with SS powersupply. (But probably most of the amp circuits identical)


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First thing first you need to check the rectifier tube GZ34 and see whether is shorted between anode and cathode. The tube rectifier fails with age and also by wrong positioning of the tube inside the amplifier. whenever the filament is playing the direct cathode role it may touch the anode and make a short circuit which bring down the power supply. Or the rectifier filament is broken causing power supply failure. Let me know what you found.