[Warren]

When listening to AM on my 47-1230 chassis I notice there is more static and hum than I think there should be and I also seem to only recieve stations around the middle of the tuning dial the stations on both the high and low ends do not come in. When listening to FM everything seems ok there I get stations all the way through the dial and I dont seem to get much static or hum. The SW bank I havent picked up any stations. Anyone have any ideas on why I am not recieving stations on AM in the high and low portions of the tuning band, or nothing on SW, but FM seems pretty good?

[Warren]

Hmmm, so far no suggestions on why the AM isnt recieving staions on the lower and upper band...just the middle portion. Hopefully someone will have an idea.

[Joeztech]

Warren;

You do not say what you may have already tried in the effort to solve the problem.

The 47-1230 model uses an approach similar to that of many other manufacturers after the war when the FM band was moved to 88-108mHz. The IF coils for the FM IF circuit are in series with the coils used for AM. The AM coils act like a signal ground for 10.7mHz IF frequencies so that when in the FM mode they do not actually do anything but pass the DC voltages to grids and plates of the various IF tubes. However when switched to the AM mode, the AM coils of the IF circuitry begin to handle the 455kHz signals for the AM circuitry. It is possible that there is a problem with one or more of the capacitors across a primary or secondary of one of the AM IF transformers. It could be due to the silver mica disease, although it is more common with sets manufactured in the 1950s it could still be an issue for your set.

One thing I would suggest first would be to use some Deoxit to clean the tube sockets and the push button switches and any switches that are involved with the AM/SW/FM band switching to see if cleaning will improve things. Sometimes just removing and re-insergint tubes into their sockets will clean both socket and pins enough to restore function if corrosion is the issue. Also just wiggling tubes in their socket can sometimes pinpoint a trouble area.

Let us know what you have tried and what results or lack of results you have and we can go from there.

Joe

[Warren]

Thanks for your response Joe... I have done a complete recap on all the paper/wax capacitors and replaced most resistors ( it did not play at all until I did the recap). I have also used deoxit on the controls and tube sockets. I have tried touching and moving the tubes around a bit to see if anything changed but haven't seen a change. Sounds like you think I should check all the mica caps also to see if they are good. I will try and check them with my meter that checks caps. I don't have a special cap checker that uses voltage when checking but maybe mine will show something.

[Jamie]

Have you aligned the radio?

[Mondial]

Do you have the loop antenna from the cabinet connected? The loop forms part of the antenna tuned circuit and the radio will not recieve properly without it on AM and SW.

[Warren]

Yes, the antenna is connected. I wont get any stations at all without it. I have not done an alignment on it yet, but the stations I do receive seem to be very close to where they should be on the dial.

[Jamie]

There is much more to an alignment than the accuracy of the dial pointer. If your radio is out of alignment, it won't get good reception. You'll get poor performance, exactly as you describe.

[Warren]

Whenever I have attempted to do an alignment I have had a hard time hearing the signal from my generator. I finally was able to hear the tone when I had the antenna disconnected and did the first part of the alignment where I set the generator to 455kc and the radio to 540kc and the generator is hooked up straight into the radio. When I try to hook up the antenna to the radio and a 6 inch antenna with 6 loops to the generator for some reason I cant always get a tone. Not sure whether its the radio or the generator but I did hear the tone when hooked straight into the radio without the antenna hooked to the generator. Maybe the tone isn't very good on the generator so when using the antenna I cant hear it, not sure. Maybe I will replace the caps, etc on the generator and see if it helps...unless someone has a better idea.

[Mondial]

If you are trying to align the 455kHz IF, you must inject the signal directly into the mixer grid circuit. The coupling loop won't work because the antenna circuit rejects the 455 IF signal since it is outside the broadcast tuning range.

The best spot to inject the IF signal is into the ant section of the tuning cap through a coupling cap of .01 uF or so. Once you have the IF aligned with the direct connection, you can remove it and use the coupling loop to align the ant circuits on AM and SW.

Unless your generator is not working there should be plenty of signal received at AM and SW frequencies with the coupling loop. Have you tried it with any other radios?

Typically, you align the low freq osc padder at 600 kHz and the high freq osc trimmer at around 1400 kHz, then the ant trimmer at 1400 for max signal. The alignment procedure should give the recommended alignment freqs for your specific model.

[Warren]

Yes, doing the IF is the part where I could hear a tone with the generator connected directly to the antenna input and no radio antenna. I will have to do some more experimanting and see if I can get a tone when usong the loop antenna on the generator and the radio antenna hooked up. I did try to get a tone on another radio, wasnt much different, although it seemed sometimes I could hear a tone. I think I will try another loop antenna and if that doesnt make a difference I will change the caps in my signal generator and see if it works a bit better. My frequency counter can see the rf signal from the generator, im just wondering if the audio tone isnt strong enough to work . I will try some things this weekend and hopefully make some progress. If anyone has any ideas to try that would be great, thanks.

[exray]

Your generator does sound like a weakling. With my old RCA generator and a foot of wire hanging out of it I can usually hear the IF across the room even on a radio with a built-in antenna.
Not to say yours has a fault...maybe its just characteristically lower output ???

[Warren]

Does anyone know how I could measure the power of the audio tone output on my RF SG ? Is there a way to measure the power of that tone?

[morzh]

Well, if your manual says what load your audio output should accept, then you connect that load equivalent (say 50 Ohm if this is what it is - I do not know, look in the manual), turn the output to max, connect voltmeter and measure RMS value (which is the default for any today's voltmeter) and then go U-square over R.
Another question, why do you need to know power when knowing Voltage is enough.

[Warren]

Actually, voltage is fine... I worded it wrong. do you know what a good strong voltage would be? I assume just need to use a volt meter on the leads to measure this?