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Hi People
Thanks for looking
This one has got me scratching my head there is something i'm overlooking here
The reported fault was turn on the sounds dropped in and out again and smell of burning
Chassis check can see one grid stopper 100R burnt up
Replaced for same and \ fitted new set of power tubes.
Replaced fuse and turned on... excessive hum , Tested all channels working ok
I removed the PI tube ( V7) ? No hum, If you remove all pre amp tubes apart from V7 and V5 Hum is present
Remove V5 hum is still present but greatly reduced
Checked with customer and prior to the fault , was working well and had zero background hum
Stolec_AC30-TB (1).pdfac30hw60.mp3
Replaced GZ34 and fitted all new pre amp tubes
Checked all grid stoppers and 1.5k all ok
Checked with another set of power tubes ( new to be sure)
All Filter are F/T caps look ok and cant see any ripple on them
I have piggybacked new caps on the filter caps still nothing
If i turn the bass fully off and treble up full i can reduce it
V5 pin 1= 273v
pin 6 & 2 =172v
pin 3 =173v
Pin 8 = 1.18v
cathode bias =10.4v around 80% Plate d
EL84 grid =321v
El84 anodes =323v
PI tube pin 1 & 6 = 232v
pi tube R71 = 52v
Amp was purchased new and never been repaired til now about 5 years old
The schematic is not the 100% version , but all seems to be the same
I think the fault is coming from the V5 circuit ??? or am i missing something
i was hoping to put up some scope pictures but mobile won't take a decent one
Thanks for looking
This one has got me scratching my head there is something i'm overlooking here
The reported fault was turn on the sounds dropped in and out again and smell of burning
Chassis check can see one grid stopper 100R burnt up
Replaced for same and \ fitted new set of power tubes.
Replaced fuse and turned on... excessive hum , Tested all channels working ok
I removed the PI tube ( V7) ? No hum, If you remove all pre amp tubes apart from V7 and V5 Hum is present
Remove V5 hum is still present but greatly reduced
Checked with customer and prior to the fault , was working well and had zero background hum
Stolec_AC30-TB (1).pdfac30hw60.mp3
Replaced GZ34 and fitted all new pre amp tubes
Checked all grid stoppers and 1.5k all ok
Checked with another set of power tubes ( new to be sure)
All Filter are F/T caps look ok and cant see any ripple on them
I have piggybacked new caps on the filter caps still nothing
If i turn the bass fully off and treble up full i can reduce it
V5 pin 1= 273v
pin 6 & 2 =172v
pin 3 =173v
Pin 8 = 1.18v
cathode bias =10.4v around 80% Plate d
EL84 grid =321v
El84 anodes =323v
PI tube pin 1 & 6 = 232v
pi tube R71 = 52v
Amp was purchased new and never been repaired til now about 5 years old
The schematic is not the 100% version , but all seems to be the same
I think the fault is coming from the V5 circuit ??? or am i missing something
i was hoping to put up some scope pictures but mobile won't take a decent one
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