AudioCircle
Audio/Video Gear and Systems => The Lab => Topic started by: filamenthead on 12 Dec 2023, 07:00 am
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hello ! i am new at this site ! i need help with an rca tube amp. the amp i have is a three channel amplifier running on the 6bq5 in p.p. , the 3rd. channel is supposed to be for the base . both left and right channels work and sound great , but the base channel i cannot figure out how to make it work properly , when i power it up after a minute or so the woofer oscillates and goes in out like crazy but no sound can be heard , this happens even when no signal is applied .
i changed coupling capacitors , power suply electrolytics caps , all resistors , i even installed new tube sockets , also tried with another output transformer , removed all components and re installed fresh new ones and still i get severe oscilation on the base speaker , with or without a signal .
can anybody out there help ! :duh:
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I will move this topic to the Lab Circle.
Found a Service Manual:
https://elektrotanya.com/rca_shc-663_3_channel_stereo_power_amplifier_sch.jpg/download.html#dl
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After the equipment warmup the circuit starts oscillate. :scratch:
I had this problem in an SS pre-amp, it was a low quality diode that worked well with a light load, but with 4 ohms speaker it started to show treble noises. Also could be cold welding or some component in the PS.
More related info:
https://www.diyaudio.com/community/threads/oscillation-in-tube-amps.145103/
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Time to bring in a pro, if you can find one. In which city do you live?
https://www.audiocircle.com/index.php?topic=90988.40
Search the whole forum for other threads about repair techs.