| Re: 200B 5 PA head hum/hiss issue [message #28121 is a reply to message #28094] |
Wed, 17 March 2021 06:04   |
stevem
Messages: 4755
Registered: June 2004
Location: NY
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Senior Member |
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Hi!
Q801 is part of the reverb pan driver circuit and I think you have said that your testing has been done with the pan not being hooked up.
If indeed this is the case then no issue that may be with any of the circuit on that input side of the pan could be getting into the audio stream.
That being said, unless your testing with a transistor tester that needs 3 of its test leads to be hooked up and is powered by a 9 volt battery then there is no guarantee that the Transistor you have tested is not going leaking in circuit when its powered up, and in turn passing some level of positive power supply voltage into the audio stream.
Also when you state that caps you have tested are right on the money uf rating wise you need a dedicated cap tester to test for leakage, you have not stated that your test out does that, if it does then all is good.
For instance, if C805-806 or especially 807are leaky then power rail voltage would be getting into the audio stream.
All of these caps a just mentioned are coupling caps which separate circuits into separate areas.
If for instance you lift the down stream end of c805 up off the board, then the whole 2 Transistor reverb return amp circuit is out of the picture for being a cause of your problem .
[Updated on: Wed, 17 March 2021 07:37] Report message to a moderator |
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