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Rookie Question - Radio Alignment - Printable Version

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Rookie Question - Radio Alignment - kstesney - 07-20-2006

Icon_confused I am in the learning phase of radio repair/restoration. I have kind of taken it up as a hobby and it has been pretty enjoyable and relaxing so far. I can't do much yet except maybe replace capacitors and wires and hope for the best. I would like to learn how to align a radio but I don't understand alignment instructions and have not found a good source that explains exactly what to do. I know I have to get an RF signal generator, but even if I had one I would not know what to do with it. I have read alignment instructions that come with the schematics sometimes but I don't know how to interpret the instructions, where or how to attach the RF signal generator or what to do to actually align the radio. Is it over my head that requires special technical schooling or does anybody know a source where step-by-step instructions are provided on how to align a radio? Thanks.

- Bill Hutchinson - 07-20-2006

To a certain extent, it depends on the model radio you're working on - what I mean is that an AA5 radio will be different than a 10 tube console.

The method I can give you at the moment will not be perfect by any means, but it will get you in the ballpark. It's a "down 'n dirty" way of alignment without a signal generator.

Tune the radio to a local station preferably around 1400-1500. Then tweak each of the IF transformer slugs until the station gets louder - you'll notice a definite peak for each slug you tune. Start with the one closest to the tuning condenser. Then move on to the next one and do the same thing. When the IF's are done, you'll also notice some small adjustment screws on the tuning condenser. Do the same thing with these adjustments.

Short of having a signal generator, this should get you close, although if you look up the schematic for your particular radio, typically there are alignment instructions available for you to follow. Again, this method is far from perfect, but the radio should perform better than wehen you started. This method works on most any make of radio.

A footnote - if you don't get favorable results at one particular point, turn the slug or screw back to approximately where you started and move on to the next point.

Again, this should get you in the ballpark. Good luck!

Bill

- kstesney - 07-20-2006

8) That's neat. The radio is a PT-28, a neat little 5-tube radio. I did adjust the IF transformer slugs ( I assume that's the two little screws inside the metal housing looking down from the top). I noticed that the station at the low frequency (which is weak even under good conditions) did get louder. Then I adjusted one of the screws on the tuning condenser (again, assuming you are talking about the two screws side by side atop the tuning blades). The station got a little louder. But I am missing one of the tuning screws. I tried using one from another Philco radio I am working on, but it did not seem to fit. It was too tight and I stopped trying before I damaged something. When I tuned the radio to a better station, it came in pretty loud, but the voices sound garbled and there seemed to be a lot of vibration in the speaker.

Any more suggestions about the alignment (missing screw) and possible symptoms of garbled reception? The caps have all been replaced and I think the tubes are OK. I did not change any resistors.

Thanks again.

Karl

- Bill Hutchinson - 07-20-2006

I'm not familiar too much with that particular model, but don't go looking too hard for a replacement screw. It's very possible that your model didn't use one in that position.

You said you tuned to a low frequency - what was it? Ideally, this works better when tuned to something at the higher end of the dial. Try the process again tuning in something at the upper end and see if it works better. Good luck!

Bill

Better... but still have a way to go - kstesney - 07-24-2006

OK, thanks again for that hint on how to align a radio without an RF signal generator. That should prove quite useful in future radio work. I did notice I was able to improve the sound to a certain optimal attainable volume and sound quality, but it is still far from perfect. I don't know if it partly due to the fact that one of the tuning screws is missing on the tuning condenser or some other reason like faulty resistors. I am going to work on relacing some of the resistors and see if that helps any. Thanks again for your help. Karl

- Chuck Schwark - 07-24-2006

Check ALL resistors, but only replace any that are outside +/-20% of nominal value.

Eureka! - kstesney - 08-06-2006

Icon_exclaim While awaiting resistors for my Philco PT28 as a last resort to improve reception, I discovered something while tinkering around. When I touch the top of the radio near the antenna with one hand and simultaneously touch the chassis anywhere else with my other hand, the radio suddenly plays loud and clear with no hum or static! That is encouraging in that it seems that the radio is on the verge of playing pefectly, but somehow I can't get the reception it needs unless I touch the radio with both hands. Ever have this kind of problem? What seems to be the problem? Thanks.

- Chuck Schwark - 08-06-2006

Sounds like the loop antenna on the back has an open (broken) connection, and your hands are providing better signal coupling to the set.

Check the loop, coil #3 in the schematic and also the external antenna transformer #2 for continuity.