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Philco 42-355 am reception - Printable Version

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Philco 42-355 am reception - sparkin' chassis - 03-02-2013

after recapping and cleaning the band selector/presets i could only get one faint station at night. after adjusting trimmers i can get a good amount of stations but none above 800 on the dial. does this sound like an alignment issue?

RE: Philco 42-355 am reception - morzh - 03-02-2013

Maybe you just don't have anything there that is receivable.
Do you have another radio to compare to?

RE: Philco 42-355 am reception - sparkin' chassis - 03-03-2013

I have several local stations in the 1300-1400s, and they come in fine on other radios. but it does not even get the high powered stations above 800 at night. the stations below 800 come in just as good as on other radios.

RE: Philco 42-355 am reception - Raleigh - 03-03-2013

I had a similar problem with a much simpler radio after I took the chassis out to measure the AVC voltage. When I put it back together I discovered a tube had mysteriously blown a filament (probably my ham hands with the meter). When I replaced the tube, the radio would only receive the lower half of the dial.

I tore my hair out trying to think of anything that would cause such a sudden loss of the upper frequencies. As a last resort, I walked through the alignment from start to finish, and darned if that wasn't what it was. I still have no idea what caused it, but careful alignment fixed it.

Your radio is much more complex, of course, so that might not be it.

RE: Philco 42-355 am reception - Raleigh - 03-03-2013

I just remembered that I had weak reception on the LOWER part of the band when I finished recapping my 42-355. Chuck Schwark suggested that I might have an open antenna coil. I did. It was an easy repair, and it fixed my reception problem.

http://philcoradio.com/phorum/showthread.php?tid=2018&highlight=42-355 is the thread where Chuck suggested the antenna coil. Of course, my symptoms were different.

You might try to see if the push button tuning brings in your upper frequency stations. If the push buttons can tune in the higher frequencies, then it'll be a clue about what's going on.

Can you receive SW across the band?

RE: Philco 42-355 am reception - sparkin' chassis - 03-03-2013

oscillator coil tested not open, so decided to try an alignment. now i get the top 3/4 of the am band fine but the bottom of the band oscillates, when i adjust for the bottom section of the band the top oscillates.

RE: Philco 42-355 am reception - Raleigh - 03-04-2013

Try setting the push buttons. If they tune in high frequency stations or you can get them to tune with your signal generator, that'll tell you if the local oscillator and mixer are working at all frequencies. Ditto if you can tune in SW.

Anything you try will eliminate one thing or another as the cause. If SW works, then something involved in AM only is the cause. If the push buttons work, it's something involved only in the dial tuning. If neither of those things work, then zero in on the oscillator or mixer. It shouldn't be anything but the oscillator or mixer if you are actually getting good reception from the lower part of the band and if you can align all the IF cans with your signal generator.

Check or re-check resistors in the oscillator circuit.

Are you testing with the loop antenna or a long piece of wire connected to the antenna terminals? I use a long wire for test, but these radios will not align properly without the loop. Place the cabinet and the chassis back to back and connect the loop antenna to the correct terminals. This way you have access to all the compensators you might not be able to reach with the chassis installed in the cabinet. Try to realign with the loop connected. (You SHOULD be able to get all AM frequencies with a wire, but when you connect the loop the dial alignment will change. It is just possible, though, that a wire might make it difficult to bring in all frequencies on the band.)

Mica caps aren't often bad, but they are sometimes. They are nearly impossible to test in the radio because meter leads have enough capacitance that it can be hard to get reliable readings from low-capacitance micas. In some of these 40s radios there are large, thin, rectangular wax covered mica caps in the oscillator circuits that could be suspect. The 42-355 has at least two of them, but I don't remember if they are in the AM tuning circuits. If they are, you might try to replace them with modern silver micas. Any of the micas between #9 and #18, say, might be suspect. The "domino" packaged micas could also be bad. They usually aren't, but I've seen enough that are.

If I have to remove a mica to test it, I just replace it. It is just easier that way, and more reliable.

Old triode oscillator tubes are funny. Sometimes one will work as a mixer but not oscillate properly. If neither push buttons or SW work, you might try to switch your two XXLs to see if it makes a difference. If you have NOS spares, plug them to test. (If no difference with NOS tubes, I'd switch back to the originals to keep the NOS tubes from being "used.")

If you have a bad trimmer (compensator) it might limit what frequency range you can align to. If your push buttons work, consider checking those out. Blow them out with canned air and checked for cracked or missing mica. Do any of them act funny, like make no difference until you crank them down hard or something like that? Once again, if your push buttons and SW work you can zero in on the trimmers or whatever other components involve only AM. (#6, #6E, #6F.)

One final suggestion is that the tuning condensers sometimes short between plates in some parts of their travel but not others. I don't think a shorted tuning condenser matches your symptoms, but it's one thing to try if all else fails. By the way, a bad tuning condenser would show up in SW as well as AM.

Summary: 1) Test with the actual loop antenna & realign. 2) Insert a modulated high frequency (1300 - 1500 KHz or so) into the antenna terminals (or, better, use a coil of wire held close to the loop) to see if you get an audio signal out. 3) Make sure the the push buttons work at your problem high frequencies and that the SW works. If they don't, something in the the oscillator or mixer circuit is suspect (probably the oscillator.) If they do work, then a coil, cap, compensator, or resistor that affects AM dial tuning only is probably bad.

Let me know your results & maybe they will spark new ideas.

RE: Philco 42-355 am reception - sparkin' chassis - 03-04-2013

Tried an alignment with the loop antenna connected. the bottom of the am band is weaker than the top. a local station at 550 came in weak during the day, but at night i cant get anything below 750. but it can receive a signal from the generator 5 feet away on this lower part of the am band. the short wave seems to work it if the volume is 3/4 of the way up. now the push buttons that worked won't receive anything even a signal generator.

RE: Philco 42-355 am reception - Raleigh - 03-05-2013

Ok, very confusing. Push buttons worked but now won't? SW works only with partial volume? Do I understand right?

Please describe function of SW. How does it work across the band? What effect does the volume control have? Please be as specific as possible.

Frustrating stuff. Bear with us. I know we can figure this out.

RE: Philco 42-355 am reception - Ron Ramirez - 03-05-2013

How are you aligning your set? Are you following the factory instructions to the letter? Very weak signal injected into the set from the signal generator and volume control of the radio at max?

Also, when aligning the low end padder at 580 kc, you must "rock" the tuning condenser to achieve best alignment. The 42-355/390 Service Bulletin describes this procedure well, although they call it "rolling." The goal here is not to get your dial pointer right at 58 on the dial, but to align for maximum output so that the oscillator is accurately tracking with the set's IF. If this is not done properly, your set will never work at its fullest potential.

RE: Philco 42-355 am reception - kporter - 03-05-2013

Hence the phrase "Rock and Roll".

RE: Philco 42-355 am reception - Ron Ramirez - 03-06-2013

...which the Boswell Sisters sang about circa 1934:

[Video: http://www.youtube.com/watch?v=6b5oWwFUhN0]

RE: Philco 42-355 am reception - Steve Davis - 03-06-2013

Wow, a lot of work went into building the set in that video!

Steve

RE: Philco 42-355 am reception - morzh - 03-06-2013

Now you just have the computer animation.

RE: Philco 42-355 am reception - sparkin' chassis - 03-08-2013

Thanks for the advice, it's better but the push buttons still don't work. Also adjustment 33a seems to have no effect when aligning IF cans. i think but am not sure that i wired a capacitor to the wrong terminal in the front end. i am going to have to go over the schematic and figure that out.