gfa-555 one channel hot

garth64 · 19th September 2008, 04:25 PM

I recently noticed one channel on my amp's heat sink is extremely hot while the other channel is slightly warm; I don't know if its always been that way or something has happened. Any ideas on what can cause this and what I can do to correct? The amp is vintage 1988. Thanks.

K-amps · 21st September 2008, 10:27 AM

If it is still playing music without distortion or hum, then it could be:

1) Abnormal load on one side.. shorted coils? Remove the speakers to see if condition persists.
2) Bias needs setting... check the bias on both channels ensure they are within 1-2 mVdc across the TP or across the emitter resistors for both channels. I forget the exact setting but 10mVdc across the tp seems fine as reference.

3) If Bias is ok, then One channel has some oscillation that would require a more indepth check up...

19th September 2008, 04:25 PM	#1
garth64 diyAudio Member Join Date: Sep 2008	gfa-555 one channel hot I recently noticed one channel on my amp's heat sink is extremely hot while the other channel is slightly warm; I don't know if its always been that way or something has happened. Any ideas on what can cause this and what I can do to correct? The amp is vintage 1988. Thanks.

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21st September 2008, 10:27 AM	#2
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	If it is still playing music without distortion or hum, then it could be: 1) Abnormal load on one side.. shorted coils? Remove the speakers to see if condition persists. 2) Bias needs setting... check the bias on both channels ensure they are within 1-2 mVdc across the TP or across the emitter resistors for both channels. I forget the exact setting but 10mVdc across the tp seems fine as reference. 3) If Bias is ok, then One channel has some oscillation that would require a more indepth check up...