Hi all,
I have this marshall ss amp on the bench that oscillates on the negative rail at around 20k. I have replaced all the transistors, caps, bias pot in the power amp section. It draws so much current, (2.4A @8vdc thru the .33 ohm mj2501 emitter resistor) I cannot power it at more than 8vdc using the variac. If I remove the wire to the base of the MJ2501, it stops oscillating and I can bring it up to 40vdc @120vac. I have another 2501 ordered although it tests good.
If anyone can help me get this thing off my bench and back to the very patient customer, I will be very grateful. See attached diag.
Thanks, Rudy
I have this marshall ss amp on the bench that oscillates on the negative rail at around 20k. I have replaced all the transistors, caps, bias pot in the power amp section. It draws so much current, (2.4A @8vdc thru the .33 ohm mj2501 emitter resistor) I cannot power it at more than 8vdc using the variac. If I remove the wire to the base of the MJ2501, it stops oscillating and I can bring it up to 40vdc @120vac. I have another 2501 ordered although it tests good.
If anyone can help me get this thing off my bench and back to the very patient customer, I will be very grateful. See attached diag.
Thanks, Rudy
It cannot drop that sort of voltage across the resistor as the protection transistor will turn on, stopping the drive. Check the components used and their orientation.
Is the MPSA06 current supply working correctly or the wrong component? Always use original type components!
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