Philco radio FM problems

5/13/2009 4:20:13 PMRalph Schneider

I am working on a Philco model 49-905 radio, the am band works fine, the fm band is weak and noisey. When I check the oscillator voltage for the fm band it is only -.6v it is supposed to be -1 to -1.5v. I checked out all of the componets that are supposed to give this problem.The one part I am stumped on is C401 it is a trimmer condenser for the fm osc. I have the philco part #, but no info on this item. When I sprayed this part with Freeze spray the radio will work fine, until it warmes back up. Is there any way I could try to replace this part with somthing generic?

5/13/2009 10:48:09 PMEdd

Of ALL of the spots in the receiver to subject to freezing chill. . . . for a cause and effect . . . .I do believe that might be the very worst, as it seems like
your description is inferring to be the trimmer capacitor associated with the FM RF oscillator section of the tuning condenser
or else that small capacitor [ Item 44] that is shown shunting the unit. If one is utilized, as per the note on the parts list.

On my supplemental info on the Riders associated with that chassis, its drawing is looking more like a piston capacitor.
At any rate, the 68 PF value given in the parts list, seems inordinately high to me. . . . considering the total capacitance of the
actual value of the ganged section of the oscillators tuning condenser.

You did not say if the unit was working withOUT that application of freeze to that area. Personally I would even expect a
normally operating unit to act squirrelly, when hit with a blast of Freon / CO2.

It producing an immediate chilling, pulling humidity from the air, and condensing water on the mica of the trimmer and wetting it
down . . . .skewing the oscillator frequency way off. . .or possibly ceasing operation at all. . . .until the unit evaporates it off.

Is the supplied pic info adequate to zero in on the part in question ?

73's de Edd

Philco_Model 49-905. . . . . . INFO :

5/13/2009 11:18:36 PMRalph Schneider

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:Of ALL of the spots in the receiver to subject to freezing chill. . . . for a cause and effect . . . .I do believe that might be the very worst, as it seems like
:your description is inferring to be the trimmer capacitor associated with the FM RF oscillator section of the tuning condenser
: or else that small capacitor [ Item 44] that is shown shunting the unit. If one is utilized, as per the note on the parts list.
:
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:On my supplemental info on the Riders associated with that chassis, its drawing is looking more like a piston capacitor.
:At any rate, the 68 PF value given in the parts list, seems inordinately high to me. . . . considering the total capacitance of the
:actual value of the ganged section of the oscillators tuning condenser.
:
:
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:You did not say if the unit was working withOUT that application of freeze to that area. Personally I would even expect a
:normally operating unit to act squirrelly, when hit with a blast of Freon / CO2.
:
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:It producing an immediate chilling, pulling humidity from the air, and condensing water on the mica of the trimmer and wetting it
:down . . . .skewing the oscillator frequency way off. . .or possibly ceasing operation at all. . . .until the unit evaporates it off.
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:Is the supplied pic info adequate to zero in on the part in question ?
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:73's de Edd
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:Philco_Model 49-905. . . . . . INFO :
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5/13/2009 11:22:39 PMRalph Schneider

The problem is the radio plays very poorly on FM and when I cool down(A-13) the piston capactor on your schematic it plays perfectly, until it warms back up,you have a Sams schematic does it have any better info on this capacitor that I have from Riders?:
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:Of ALL of the spots in the receiver to subject to freezing chill. . . . for a cause and effect . . . .I do believe that might be the very worst, as it seems like
:your description is inferring to be the trimmer capacitor associated with the FM RF oscillator section of the tuning condenser
: or else that small capacitor [ Item 44] that is shown shunting the unit. If one is utilized, as per the note on the parts list.
:
:
:
:On my supplemental info on the Riders associated with that chassis, its drawing is looking more like a piston capacitor.
:At any rate, the 68 PF value given in the parts list, seems inordinately high to me. . . . considering the total capacitance of the
:actual value of the ganged section of the oscillators tuning condenser.
:
:
:
:You did not say if the unit was working withOUT that application of freeze to that area. Personally I would even expect a
:normally operating unit to act squirrelly, when hit with a blast of Freon / CO2.
:
:
:It producing an immediate chilling, pulling humidity from the air, and condensing water on the mica of the trimmer and wetting it
:down . . . .skewing the oscillator frequency way off. . .or possibly ceasing operation at all. . . .until the unit evaporates it off.
:
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:Is the supplied pic info adequate to zero in on the part in question ?
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:73's de Edd
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5/14/2009 12:22:17 AMWarren

Did you mean # 44 Fixed trimmer ? Or A-13 Coil ?

5/14/2009 10:05:40 PMRalph

:Did you mean # 44 Fixed trimmer ? Or A-13 Coil ? The A-13 coil, they call it a condenser trimmer, FM osc.

5/14/2009 10:07:38 PMRalph

The A-13 coil, they call it a condenser trimmer, FM osc.

5/14/2009 10:36:22 PMWarren

Yes I see now A-13 is an adjutable trimmer Cap. Have you tried to adjust it ? Being it's the Osc. there should be a very noticable change when it's turned.

5/14/2009 10:48:40 PMRalph

When I adjust it it changes the frequency so I have to tune the dial off to get a station, but I do not get a clear signal until i hit the coil with frezze spray, and then it just works great for a while.

5/15/2009 2:08:14 AMWarren

Okay .. Don't think it's A-13 That is really the problem part. When you hit it with the spray, seems like just the wet is making it shift way off in frequency. By doing this is now making the oscillator work in the range it should have been. Maybe look back into the Oscillator section around the tube itself. See if something there is off as to voltage. Could be a resistor gone up in value, a backward cap, wrong cap, poor ground path. If nothing else, might take A-13 out and look it over good with a magnifier.

5/17/2009 12:20:20 PMRalph

Warren I went over every inch of the oscilator circuit like you suggested, and I finally found the culprit( bad solder joint) on the coil below the tuner, very hard to see, I resoldered all of the joints on that coil and the problem just disappeared. Thanks to everyone for all of your help, Ralph