Webcore 1754 Holiday Coronet record player hummmm issue

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Phonofilia1
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32
Nov Sat 01, 2014 2:39 am
Indianapolis Indiana

Webcore 1754 Holiday Coronet record player hummmm issue

Post by Phonofilia1 »

Hi folks. I thank all in advance for any help you can give me. I recapped this little four tube amp that has the ever popular 12AX7 pre-amp, two 35C5 power amp tubes, 35W4 rectifier. Tubes all test very good. It worked perfectly for about three days, but I started noticing a growing hum to the point it now sounds almost like I had never did the recap EXCEPT when I turn the volume up to maximum (with no record playing) and the hum drops off to nearly nothing. I thought perhaps one of my filter caps had failed, so I replaced all three, 20, 40 and 60 microfarad. Voltage rating of the original was 150 volts, but I did them in 600volts. I have re-soldered all my joints to make sure. I replaced the rectifier tube since I had one but no change. Sometimes when I touch the volume pot or chassis I hear an occasional extra hum, but not frequently. I am totally stumped. I can't find a schematic. Any suggestions?
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BikenSwim
Member
8355
Oct Wed 14, 2009 5:36 am
Queens, New York, USA

Re: Webcore 1754 Holiday Coronet record player hummmm issue

Post by BikenSwim »

Sometimes a 35C5 will hum after it has run for a while. You can change one 35C5 at a time, and even use a 50C5 from another radio if you have one, just to see.
Diode Don, All problems rectified.
Hotwax
Member
3253
Jan Tue 15, 2013 11:04 pm
Rockport Tx

Re: Webcore 1754 Holiday Coronet record player hummmm issue

Post by Hotwax »

Schematic.

Hotwax
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tubes4life
Member
8764
Aug Tue 24, 2010 7:56 pm
Jacksonville, Florida

Re: Webcore 1754 Holiday Coronet record player hummmm issue

Post by tubes4life »

This is a hot chassis set, I would not touch the chassis while it is plugged in---shock hazard.

When you said you replaced 150v caps with 600v, were you referring the electrolytics?
William
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Jim Mueller
Member
7095
Sep Mon 16, 2013 1:42 am
Tucson, Arizona U.S.A.

Re: Webcore 1754 Holiday Coronet record player hummmm issue

Post by Jim Mueller »

Actually it isn't a hot chassis set; C6 isolates the chassis and C1 isolates the tone arm wiring. Nevertheless there are still plenty of other danger spots in it. Use an isolation transformer and observe all safety precautions.
Jim Mueller

Time is SO weird!
Artcurus
Member
2035
Feb Tue 03, 2015 11:26 pm
Odessa Texas

Re: Webcore 1754 Holiday Coronet record player hummmm issue

Post by Artcurus »

Did you replace all the caps? There's a chance one of new caps has failed, theres still an old leaky cap, or you have a heater to cathode short in one of the tubes. Also grid leakage in the 35C5. Replace all the resistors around 35C5 at the very least.
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