Hi.
I am working on a reissue Marshall JTM45 and have a problem.
When I got the amp the power tubes were burnt and also one of the input jacks had slightly melted.
Not sure what had caused this.
Anyway, I changed the filter caps, retubed it and checked voltages which all seems ok.
The amp plays and sounds good.
But, there is some oscillation going on, it almost sounds like a tremolo when played.
Also you can see the power tubes glows blue in pulses!
The Bias voltage goes up and down about + - 4 volts in the same pulses.
What could cause this??
I am running JJ KT66 and vintage Siemens and Brimar preamp tubes.
The same thing happened with the old preamp tubes in, but I did not check with other power tubes.
Any help appriciated.
Regards,
Dennis
I am working on a reissue Marshall JTM45 and have a problem.
When I got the amp the power tubes were burnt and also one of the input jacks had slightly melted.
Not sure what had caused this.
Anyway, I changed the filter caps, retubed it and checked voltages which all seems ok.
The amp plays and sounds good.
But, there is some oscillation going on, it almost sounds like a tremolo when played.
Also you can see the power tubes glows blue in pulses!
The Bias voltage goes up and down about + - 4 volts in the same pulses.
What could cause this??
I am running JJ KT66 and vintage Siemens and Brimar preamp tubes.
The same thing happened with the old preamp tubes in, but I did not check with other power tubes.
Any help appriciated.
Regards,
Dennis