Hello to you all
this is my first post on here.
I do amp repairs for a bit of fun and to keep me busy now i don't work anymore . I have a basic understanding of audio and valve amps
I understand about the high voltages
this vibrolux amp i was given to look at by a friend has a noise fault. after mostly 20 - 30 mins it will start. sounds like a bad tube or noisy resistor
i have swapped the tubes out for new ones and still the same. I replaced all the anode resistors still noisy
I went and got another new set of tubes just to be sure.
the noise goes when i remove v4, but if you listen very quietly you can just about hear it
i can see the noise at the PI on the 82k and 100k on the scope ( crt type)
but i can't see the noise elsewhere . i have replaced the 82k and 100k and just about every other part in the pi stage.
All the voltages are correct apart from one Pin 3 the schematic says 17.4v i read about 70v
the noise is not hiss or a mobile phone or interference
Just to re - cap on what i have done
Changed all the tubes twice
Changed all the anode resistors
changed all the parts in the pi inc tube base
Removed V1-2-3 noisy
remove v4 the amp is quite, but you can just hear the noise,
Noise can only be seen at the PI on the 82k - 100k.
All parts are changed for new parts only
Fender-Custom-Vibrolux-Reverb-Reissue-Schematic1.pdf
I would welcome any help, i have run out of ideas
thanks in advance
Arbutt
this is my first post on here.
I do amp repairs for a bit of fun and to keep me busy now i don't work anymore . I have a basic understanding of audio and valve amps
I understand about the high voltages
this vibrolux amp i was given to look at by a friend has a noise fault. after mostly 20 - 30 mins it will start. sounds like a bad tube or noisy resistor
i have swapped the tubes out for new ones and still the same. I replaced all the anode resistors still noisy
I went and got another new set of tubes just to be sure.
the noise goes when i remove v4, but if you listen very quietly you can just about hear it
i can see the noise at the PI on the 82k and 100k on the scope ( crt type)
but i can't see the noise elsewhere . i have replaced the 82k and 100k and just about every other part in the pi stage.
All the voltages are correct apart from one Pin 3 the schematic says 17.4v i read about 70v
the noise is not hiss or a mobile phone or interference
Just to re - cap on what i have done
Changed all the tubes twice
Changed all the anode resistors
changed all the parts in the pi inc tube base
Removed V1-2-3 noisy
remove v4 the amp is quite, but you can just hear the noise,
Noise can only be seen at the PI on the 82k - 100k.
All parts are changed for new parts only
Fender-Custom-Vibrolux-Reverb-Reissue-Schematic1.pdf
I would welcome any help, i have run out of ideas
thanks in advance
Arbutt
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