philco model 89 chasis123 hum/squeal between some stations

philco model 89 chasis123 hum/squeal between some stations - Printable Version

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philco model 89 chasis123 hum/squeal between some stations - Guest - 11-10-2006

during tuning of my philco model 89 I recieve a loud hum/squeal between some stations recieved and reception is poor when radio's I.F. sections are properly tuned? what is your suggestion on solving this problem

- Chuck Schwark - 11-10-2006

Any missing tube shields? Did you move any wires around when re-capping and/or replacing resistors? Lead dress can sometimes cause this.

- Guest - 11-12-2006

Chuck, non of the problems you mentioned were evident, seems like a problem with I.F. section, when I tuned it, ie. 2nd I.F. secondary , the adjustment will not allow for max, as desired from the tune up proceedure for the radio, if you max it out, then try to tune it the radio goes into uncontrollable squeals and no tuming at all, what do you think.

- Ron Ramirez - 11-12-2006

Sounds like an oscillating IF circuit.

Did you replace the paper and electrolytic capacitors? They should ALL be replaced.

Try substituting the 39/44 IF tube with a known good one.

When you align the radio, feed it the lowest possible signal. Don't crank up your signal generator to maximum - turn up the volume control on your radio instead. Preferably, use a meter or oscilloscope for alignment, connected between the AVC line and ground. If you go by this schematic:

http://www.philcoradio.com/tech/89evol.htm

connect the NEGATIVE lead of your meter or scope to the end of resistor (21) that connects to the 1st IF secondary, and the positive lead to ground. If a meter is used, set it to the low volts range. A digital meter is not good for this; an older analog meter is much better for alignment purposes. And the oscilloscope is the best way to go, if you have one.

Using the same schematic suggested above, check resistors (18 ), (30) & (31) and be sure they are within tolerance. If not, replace. All resistors in the set should be checked to be sure they are within 20% of rated values. If not, replace them.

Only other problem I can think of would be one of the IF transformers may have gone bad - the windings are wound on a wooden form, and sealed in place with wax. Sometimes, one winding will come loose and slip down on the form, closer to the other winding. This upsets the "Q" of the circuit and causes problems.

- Guest - 11-14-2006

Thanks for the Info Chuck, the radio is at its permanent Location(it was a gift) but when I get another opportuunity to do some more work to it I will try those suggestions. Thanks Again Henry(for Wade Griffin)