I have major motorboating on my Zephyr that I am trying to bring back to life. I replaced the two 10 uf 350V electrolytics with no effect. I get a nice loud hum when I touch the phono input, so I know the audio stages are working, but the motorboating is too severe to listen to anything else. Any hints appreciated.

I would check the grid resistors in the audio stages,but from what I understand,an open grid resistor in any stage can cause motorboating.I just overhauled a mid nineteen-thirties Vega instrument amplifier that was doing the same thing.The wire connected to the grid-cap of the 6c8g pre-amp tube was broken at the solder joint.Certainly sounded like my old Evinrude was right there beside me:put,put,put,put,etc.Good luck.

:I have major motorboating on my Zephyr that I am trying to bring back to life. I replaced the two 10 uf 350V electrolytics with no effect. I get a nice loud hum when I touch the phono input, so I know the audio stages are working, but the motorboating is too severe to listen to anything else. Any hints appreciated.

John,

All paper capacitors should be checked for leakage. Leaky/shorted capacitors or capacitors that have opened or lost capacitance can cause all kinds of problems in a radio. All tube shields (if used) should be in place and making good contact with the chassis.

Radiodoc

John, you might try pulling tubes, one at a time, to see if you can pinpoint the stage where the motorboating is originating.

Doug

:I have major motorboating on my Zephyr that I am trying to bring back to life. I replaced the two 10 uf 350V electrolytics with no effect. I get a nice loud hum when I touch the phono input, so I know the audio stages are working, but the motorboating is too severe to listen to anything else. Any hints appreciated.