Another 48-482 - Printable Version
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RE: Another 48-482 - mikethedruid - 08-26-2021
In some ways this is going to be a situation of the blind leading the blind. I lucked out with this second 48-482 I restored in that when I was all done with the re-cap, the FM was working very well. I really did nothing more than slight adjustment of the odd little condensers atop the main tuning condenser to get it right on tuning wise and maximum strength. I did that just with a ruler at the base of the dial plate as shown in the alignment instructions, finding a station, hearing its frequency when they said it, and then using the ruler and dial reference in the instructions to dial it in exactly.
You will find a different, and better explained, set of alignment instructions for FM in the Rider manuals, volume 18, Philco pages 93 - 107. I have used it to set the FM IF frequency, and do general FM alignment. It does work, and does not require an FM signal generator. I will probably use that, and trust in luck when I go back and try to get the FM on the first one I restored working as well as the FM works on this latest one. I strongly suggest getting a set of the high resolution scanned CDs of the Rider Manuals. You can find them on eBay. https://www.ebay.com/itm/110552444760?hash=item19bd706f58:g:LtoAAMXQLbVRaB6W Well worth the money ! Or, you can use Nostalgia Air's scans, which are not as high res, but will work. http://www.nostalgiaair.org/Resources/637/M0013637.htm (Yours is: http://www.nostalgiaair.org/Resources/617/M0013617.htm ) Using both the pictures from the Philco pages on this site for the location of various components used in alignment, and the Rider instructions we should be able to get thing working as we wish. By the way, do you have the built in antenna hooked up to the little 4 pin socket on the chassis back? It goes from the plug through a wire 20 inches long to a little metal clamp that goes around the power cord, and capacitively uses the cord as an antenna. It works very well on my radio, and was what I used for tweaking the alignment. If you have the little plug, wire and clamp you are in luck. If not you'll have to mouse something up. You can use a 1 inch square piece of steel tin can (not aluminum) for the little piece that clamps around the line cord. The 20 inch length of the wire to the clamp is important, and slide it back and forth a bit on the line cord until it gives you the best signal. It should be about 18 inches give or take a bit from where the line cord comes out of the chassis.
So good luck to you. I will need it myself when I tackle the first one I restored again. Also, if, with the antenna hooked up properly, your FM seems to be working OK, don't go crazy. Better to leave well enough alone.
RE: Another 48-482 - Bigreddog42 - 08-27-2021
Thanks for the tips. I’ve got the riders docs. They contain the same instructions as the Philco service manual. The manual on this site is more legible. Thanks to the guy that loaded all that stuff! I do have the same antenna connector but the leads are stapled to the cabinet - a simple dipole arrangement. My set picks up the 2 or 3 strong FM stations in my area but I am hoping with alignment I’ll be able to receive some stations in the Raleigh-Durham area about 70-90 miles away. On the other hand I am a little nervous about screwing up what I have - pretty fine sound out of the big 12” speaker. I think I’ll start like you and just adjust the tuning condenser and see what I get. If it’s not a lot better then I’ll adjust the IF. I’ll let you know how it works out.
RE: Another 48-482 - mikethedruid - 08-27-2021
If your FM stations are coming in at the right places on the dial, then the oscillator is probably right on, so you don't want to screw with that trimmer. If not, then you can use that station to tune the trimmer until it comes in where it should. You will also need to adjust the RF sections for maximum volume. You can also peak the IF using the jumper on the FM-1000 socket, and a regular signal generator. I suggest using a good digital receiver to double check the signal generator output. For FM it should be 910 KC. This uses the other trimmer screw on the IF can, so BE CAREFUL of that or you'll screw up the AM and SW. Look at the picture to make sure you are using the right trimmer on the IF, as well as the ones on the tuning condenser. Good luck.
RE: Another 48-482 - Bigreddog42 - 09-01-2021
Good evening. Here's the alignment update. I pretty much followed the procedure in the 48-1270 service manual (similar if not the same as 48-482). Since I did the AM/SW alignment a couple of months back I decided to redo as I now have a frequency counter. That was all pretty straight forward. The FM alignment was straight forward also - just a bit tedious with the jumper, loading network and various places to hook up sig. generator. The IF alignment really woke up the radio. I can tune in a lot of FM stations now. Not as good as the modern digital radio in my car but pretty darn good. I can get several Raleigh-Durham stations now. I decide to go ahead with the oscillator also. The procedure aimed for a zero beat when turning the trimmers. I never was not able to obtain a zero beat so I put trimmers back where they were originally. After removing the jumpers I selected a strong station and tuned the trimmer for strong clear signal. A bit unorthodox but I am pretty satisfied with result. Oh yeah, the procedure also involves adjusting the spread of the FM coils (L406, L407, L408) for tuning the lower frequencies. I skipped that part. I did not want to risk damaging those old things.
Going to put it back in the cabinet tomorrow after I go over all the ground connections (got a tiny bit of hum that is only detectable when there is no audio signal like between record changes or untuned stations). If I don't find something obvious pretty quick I'm just going to ignore it.
There is one more oddity. On FM 103.7 there is a fairly loud hum when that station is tuned (only one that does this). I get the same hum on another vintage FM radio, !947 Zenith. I don't think I hear it on my car radios. You know of something I might be able to do to eliminate that? I've unplugged everything in my house to eliminate stuff like chargers, bug repellers etc. One thing in the back of my mind is that I replaced the old wave trap with just a capacitor. Wonder if that's the culprit. Of course the Zenith has same problem (I didn't restore that radio). I might start a separate thread on this issue.
I sure appreciate your help.
RE: Another 48-482 - mikethedruid - 09-01-2021
If that hum problem only happens on that one station, and you notice it on more than one radio, I would say that the hum is actually coming from the station. It happens. I wouldn't worry about it. I'm glad to hear you got the FM up and working well.
Congratulations !
RE: Another 48-482 - mikethedruid - 09-02-2021
DEMONSTRATION OF FINISHED 48-482
[Video: https://www.youtube.com/watch?v=44J-EAKaVvY]