Hi all I just returned to the workshop a conrad johnson pv10b without RIAA that makes me a strange thing. when I started it it was spitting and blowing on the right channel like a lamp at the end of its life or a feeding problem.
I open it, I find two 12au7 EI new in, I test them both, they are perfect, I reverse them and the problem moves too, suddenly I change the tube that poses problem with another that is good, the problem persists, I still change for a 12au7wa CIFTé military and the same ...
I take an old ECC82 harman kardon end of life and it works, I retest with another ecc82 mazda 5 star and it works too. So, I think I must be crazy or something, but if in doubt, I change the two tube support, I control all the power, the heating and everything is perfect. So, I'm doing a test with a new ECC802s and he starts to spit and blow again. moreover, no matter which tube I put on it, it is super microphonic.
Any ideas ?
I open it, I find two 12au7 EI new in, I test them both, they are perfect, I reverse them and the problem moves too, suddenly I change the tube that poses problem with another that is good, the problem persists, I still change for a 12au7wa CIFTé military and the same ...
I take an old ECC82 harman kardon end of life and it works, I retest with another ecc82 mazda 5 star and it works too. So, I think I must be crazy or something, but if in doubt, I change the two tube support, I control all the power, the heating and everything is perfect. So, I'm doing a test with a new ECC802s and he starts to spit and blow again. moreover, no matter which tube I put on it, it is super microphonic.
Any ideas ?
so, I changed
both sockets (high-end ceramics)
decoupling capacitors (all)
checked all welds
controlled the power supply HT
controlled the regulated supply of heating
in fact it works very well but I can not run it with these two ecc82, it "rejects" all others while they work perfectly in my other devices and it is ok on my tester "sencore MU140"
that's why I titled my thread "strange conrad johnson"
both sockets (high-end ceramics)
decoupling capacitors (all)
checked all welds
controlled the power supply HT
controlled the regulated supply of heating
in fact it works very well but I can not run it with these two ecc82, it "rejects" all others while they work perfectly in my other devices and it is ok on my tester "sencore MU140"
that's why I titled my thread "strange conrad johnson"
Start by inputting a small signal, and monitoring the output. Poke around with an insulated tool,
like a pencil eraser, plastic stick, etc. Look for a sensitive place on the board, remembering
that it's high voltage. The output sine may go on and off or distort. Trigger on the input, so you
always have a steady trace, even if the output goes away. Connect the scope probe's
ground clip to the chassis. See if the noise is there even if the input is turned off.
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