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Old 20th October 2010, 11:04 AM   #1
trondkj is offline trondkj  Norway
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Join Date: Mar 2006
Location: Borealis
Default 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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Old 25th November 2010, 08:22 PM   #2
diyAudio Member
Join Date: Nov 2010
Default Schematic

Hi Trondkj,
I don't know this amp but here is the schematic (right channel). Sorry, it's a french version. Hope this help you. Good luck !
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Old 26th November 2010, 01:02 AM   #3
pedroskova's Avatar
Join Date: Dec 2002
Location: C'ville VA, USA
Just a guess, but the sound "fading away" might point to the power supply dying... maybe your rectifier tube?

You should also replace the old electrolytic cap(s) in the psu if you get it up and going again.
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Old 11th September 2011, 04:34 PM   #4
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Join Date: Sep 2011
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.
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