I'm experiencing distorted sound on my counterpoint after installing IRFP240 and 9240. Can someone assist with repairs please
In what way have you redesigned the output stage to ba able to use IRFP240 and 9240.
The original have no source resistors and it's extremely tricky, if not impossible, to keep them thermally stable without some source resistors.
I have a service manual PDF for SA-20 and SA220 (one of the variants anyway) avaliable. Might be helpful when repairing and try to find out what causes the problem.
Have you managed to set the bias correctly and got the right standby current through the output mosfets?
Personally I would aim for Exicon's in this circuit and rebuild the bias circuitry. but that is a bigger re-design that need some thought and knowledge.
As per the original designers ideas it really are a bliss to get rid of those source resistors for improvement of sound quality.
With Exicon's you can do that, but they are bit softer and weaker than the originals.
The tube part are to weak to really drive the Mosfets. A doubling of the stand by current in the follower would be good, but that will not be easy, so you better be a skilled soldering hobbyist to do that. Not sure the transformer can handle another 300mA heater load. Better check that too before trying to add another parallell tube to the cathode follower.
The service manual are avaliable on internet as a 23 page PDF, but I don't remember where I found it.
Send me a PM with your e-mail address if you would like to have it.
The original have no source resistors and it's extremely tricky, if not impossible, to keep them thermally stable without some source resistors.
I have a service manual PDF for SA-20 and SA220 (one of the variants anyway) avaliable. Might be helpful when repairing and try to find out what causes the problem.
Have you managed to set the bias correctly and got the right standby current through the output mosfets?
Personally I would aim for Exicon's in this circuit and rebuild the bias circuitry. but that is a bigger re-design that need some thought and knowledge.
As per the original designers ideas it really are a bliss to get rid of those source resistors for improvement of sound quality.
With Exicon's you can do that, but they are bit softer and weaker than the originals.
The tube part are to weak to really drive the Mosfets. A doubling of the stand by current in the follower would be good, but that will not be easy, so you better be a skilled soldering hobbyist to do that. Not sure the transformer can handle another 300mA heater load. Better check that too before trying to add another parallell tube to the cathode follower.
The service manual are avaliable on internet as a 23 page PDF, but I don't remember where I found it.
Send me a PM with your e-mail address if you would like to have it.
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