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Atwater Kent 84 question - Printable Version

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Atwater Kent 84 question - fields 100 - 09-27-2014

As soon as I turn the power "on", I get 60HZ hum. With volume pot  100% off. It starts with all tubes being cool, and stays there during operation. The hum level is low, so it is not heard during receiving the station. Otherwise the set operates flawlessly. Does not respond to the volume level change. Before I start digging deep, I thought there may be some obvious remedy simple for everyone but me. The set has been completely redone electronically, with all capacitors replaced.Thanks.


http://www.nostalgiaair.org/PagesByModel/491/M0001491.pdf

RE: Atwater Kent 84 question - morzh - 09-27-2014

Grounds.

Check all your gound rivets, also ground pins in your tube sockets.

RE: Atwater Kent 84 question - Mondial - 09-27-2014

Check the two 10 ohm filament shunt resistors (flex type). If one of these is open it will cause a hum. 

These two resistors set the electrical center of the 2.5V filament winding which is referenced to ground. They perform the same function as a center tap of the filament winding. This is important because the 47 output tube has a directly heated filament, so to cancel hum the two filament pins must be balanced to ground.

RE: Atwater Kent 84 question - fields 100 - 09-28-2014

Mondial,

Bull's eye! Funny, before I put the chassis into the cabinet there was no hum. Also, all resistors, incl. the flex. ones, had been checked. Guess, one flex. resistor went bad just within these several weeks. Thanks a lot.

RE: Atwater Kent 84 question - AI2V - 10-04-2014

Those flex resistors are notoriously bad;  I replace them whenever I come across them.  A common metal film , usually a half watt, resistor works fine.  When the radio was built there were no low value resistors other than the wire type.