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Good morning/afternoon too you all
Ok this one has beaten me and im beginning to do my head in and want to get rid of. But ive never in my life had a valve amp beat me
This amp came in from a regular customer ( Harp player ). I aint seen it for about 2 yrs. Report was it was making noise and smoking
I didnt test it i went in to find the cause of the smoke. I found a cap ( C28 ) blown its guts out and R34 was burnt up
Changed them both and the op amp. Tested the amp a high pitched whine. So fitted new EL84's still the same Swapped
out all 12ax7s .. so all new tubes still high pitched whine with some background noise
Injected a signal in to input and used send to another power amp clean signal no noise
Injected a signal into return and connected up speaker .. high pitched whine. but the signal source where its guitar / audio or sinewave all sound good
noise without any input .mp3
Noise with audio playing .mp3
Voltage on EL84s removed
Pin 2 = -15v
Pin 7 and pin 9 = 396v
Voltage on EL84s fitted
Pin 2 = -12v
Pin 7 = 330v
Pin 9 = 290v
heater good at 6.3v
V1 - V2
Pin 1 = 170v
Pin 6 = 190v
Pin 3-8 = 1.1v
V3
pin 1 = 198v
pin 6 = 230v
pin 3 = 1.1v
Pin 8 = 60v
-15v rail and -36v rail all correct
Checked visually and resoldered all links and buzzed though
checked disabled reverb circuit
No noise or hum on HT filter caps and all look ok not leaking
checked and disconnected NFB
Now while testing and trying to find the source of the noise i connected up the dummy load as well as the speaker. i found the whining noise went away, Disconnect the dummy load and it comes back
( one thing i did find was another speaker jack lead soldered to the the speaker terminals . Not sure he was plugging another speaker on or not )
Final note. Im beginning to think it a possible board like Marshall DSL's or tube base issue. Myself im un aware of any known issues
look forward to your reply's
Ok this one has beaten me and im beginning to do my head in and want to get rid of. But ive never in my life had a valve amp beat me
This amp came in from a regular customer ( Harp player ). I aint seen it for about 2 yrs. Report was it was making noise and smoking
I didnt test it i went in to find the cause of the smoke. I found a cap ( C28 ) blown its guts out and R34 was burnt up
Changed them both and the op amp. Tested the amp a high pitched whine. So fitted new EL84's still the same Swapped
out all 12ax7s .. so all new tubes still high pitched whine with some background noise
Injected a signal in to input and used send to another power amp clean signal no noise
Injected a signal into return and connected up speaker .. high pitched whine. but the signal source where its guitar / audio or sinewave all sound good
noise without any input .mp3
Noise with audio playing .mp3
Voltage on EL84s removed
Pin 2 = -15v
Pin 7 and pin 9 = 396v
Voltage on EL84s fitted
Pin 2 = -12v
Pin 7 = 330v
Pin 9 = 290v
heater good at 6.3v
V1 - V2
Pin 1 = 170v
Pin 6 = 190v
Pin 3-8 = 1.1v
V3
pin 1 = 198v
pin 6 = 230v
pin 3 = 1.1v
Pin 8 = 60v
-15v rail and -36v rail all correct
Checked visually and resoldered all links and buzzed though
checked disabled reverb circuit
No noise or hum on HT filter caps and all look ok not leaking
checked and disconnected NFB
Now while testing and trying to find the source of the noise i connected up the dummy load as well as the speaker. i found the whining noise went away, Disconnect the dummy load and it comes back
( one thing i did find was another speaker jack lead soldered to the the speaker terminals . Not sure he was plugging another speaker on or not )
Final note. Im beginning to think it a possible board like Marshall DSL's or tube base issue. Myself im un aware of any known issues
look forward to your reply's
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