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Won't pickup stations but will pick up am transmitter - Printable Version

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Won't pickup stations but will pick up am transmitter - ODPILOT - 12-10-2023

I have restored 2 of these (53-1750) Philco's.  One of them recently stopped picking up AM radio stations - just a lot of buzzing throughout the tuning dial.  I have a small AM transmitter (purchased on ebay) which I can plug into the headphone jack in my computer (or any audio source) and  when placing the transmitter on the Philco, the Philco receives and plays the signal just fine at any frequency I choose.  

I checked the continuity of the Philco antenna - seems good and even hooked up an auxillary AM antenna, still no stations.  I've tested all the tubes, they're all good AND even swapped the tubes from the other Philco and still no stations, only buzzing.   I've have not tried re-aligning it but why would the alignment have gone bad when it was fine? 

I've checked all the connections in the radio, nothing loose, all caps are only a couple of years old, but maybe recap it again??   Not sure where to start looking for the issue in this thing.   It does work with the AM transmitter (see photo) that should be giving me some clue as to the problem, but not sure what.  Any ideas?  Thnx,

               

RE: Won't pickup stations but will pick up am transmitter - morzh - 12-10-2023

I do not see the sch of this radio on Nostalgiaair, so I do not know exactly what's there, but:

If it does have more than one RF stage, check the 1st one (well, all of them) for tubes and RF coils integrity.
There could be enough signal land tuning left with one stage bad; I had that problem on my black dial Zenith. Worked fine, but sensitivity was down.

Start with ohming coils, checking tubes, measuring voltages on RF stages.

RE: Won't pickup stations but will pick up am transmitter - David - 12-10-2023

Found some info at 2 links plus beitman the 53-1350 an 53-1750 are the same. https://www.radiomuseum.org/r/philco_chairside_radio_53_1350_53_1750.html   https://antiqueradios.com/forums/viewtopic.php?t=95516        

RE: Won't pickup stations but will pick up am transmitter - MrFixr55 - 12-11-2023

Hmmm...

Other radio or radios work fine in the same environment?

Does the freq indicated on the transmitter match the frequency on the radio's dial?

Is there background noise when receiving your AM Transmitter. Does the radio become noisy when left at that freq and the transmitter is turned off?

Is your AM transmitter received broadly on the receiver in question, or only at the freq indicated on the receive dial?

The schematic shows a cap, C19, 0.047 uF across the power line to filter power line noise. check / change this cap with a safety type.

The schematic shows a tunable LC network and switch (S2) in the input of the converter, ganged to another coil in the oscillator which serves as a wave trap (?). Try to set switch so that this network is out of the circuit.

Check / change C3, the 725pF cap that connects the loop antenna to the converter input. It is likely mica. They usually do not fail, but very occasionally, they do.

I worked on one of these as a kid. The voltage doubler rectifier allows greater power out of the 35L6. This plus the 8" speaker makes this a nice sounding set.

RE: Won't pickup stations but will pick up am transmitter - DaleHCook - 12-11-2023

The original Philco service information for this model is available on this site in the Philco Library. Use the Philco Service Index to find it.

RE: Won't pickup stations but will pick up am transmitter - David - 12-11-2023

Time for a real stupid question! What is the distance of your transmitter from the set? Maybe the set is turned to phonograph not radio somehow the phonograph is picking up the signal! Like I said stupid question based on something that happen to me in my youth.

RE: Won't pickup stations but will pick up am transmitter - DaleHCook - 12-11-2023

Any question based upon personal experience is not a stupid question.

He that is without electronic servicing error among you, let him first cast a stone.

RE: Won't pickup stations but will pick up am transmitter - ODPILOT - 12-11-2023

MrFixr55 - yes, other am radios are able to pickup the stations no problem. When tuned to the AM transmitter, there is no background noise and when I turn off the AM transmitter, yes there is buzzing. The caps you mention are only a couple of years old and I had already replaced the original mica cap but I'll replace the caps you mentioned anyway, we'll see what happens. The AM transmitter can be set to any AM frequency and the Philco is able to pickup up any frequency I set it to. The tune dial on the Philco seems to be accurate with the frequency being transmitted.

DaleHCook - I do have the schematic for it - thanks.

David - The Philco was set to radio not phono. The AM transmitter, as you can see in the photo, sits on top of the Philco - just inches from the antenna underneath. It's a very weak AM transmitter but the radio seems to pick it up just fine.

RE: Won't pickup stations but will pick up am transmitter - David - 12-12-2023

If you have a NOS 7A8 try that. Might try a piece of wire 6 feet+ connected as a ext ant. If no luck check all coils and other items around the 7A8. David

RE: Won't pickup stations but will pick up am transmitter - jtiner - 12-14-2023

Is it possible that a new noise source is positioned near this radio / loop direction so that it overwhelms local stations (but not your transmitter sitting on top) for this radio only and not your others? Perhaps a device with a switching power supply or Christmas light control box, etc? It seems unlikely based on your description, but easy to rule out.