Re: Dynaco Mark VI problem : Hum, low B+ and no signal after replacing 22 ohm

Because of the lack of experience, test equip, etc, try replacing the
bias rectifier, and the bias smoothing caps, or at least temporarily
swap each one, to make sure one isn't drawing current. And as
mentioned, replace the coupling caps on the outputs.

Remember, the bias is negative, so orient the caps properly, as well as
the diode.

A higher resolution scan would also help on this end : ).

Good luck,
Bob H.


Mark in Philly wrote:
Hello group,
I need the assistance of a tube amp expert to help me sort out a
problem I have with a Mark VI amp. I burned out 2 of the 22 ohm
resistors while running a poor tube. Upon replacement of the resistors,
I get only hum at the outputs, but I do get a pop when I insert and
remove an input cable carrying a signal.

The resistors are the high wattage resistors between the 8417 output
tube and output transformer taps, R109 and R111 as shown in the
schematic that can be found at:
http://www.geocities.com/vintageaudio/markvi.jpg

Upon running the stock voltage tests, I see I have about 80% B+
voltage, which likewise proportionately affects all other downstream
voltages.

This sound likes a power supply problem, but I'm just a hack. Any ideas
on how to diagnose further?

Other pertinent info: the amp exhibited some hum just before I fried
the resistors, but prior to that was working fine. I double checked all
the wiring and voltages against another properly working amplifier.

As always, any help is greatly appreciated.

Mark in Philly.

.

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