[mikethedruid]

Hi ! First, let me introduce myself. I am a retired EE. I began to collect antique radios when I was 12 years old, a half century ago. My current project is a 48-482. You can see a before picture of it in the table radios forum.

I bought the radio on eBay, and got it for what I consider a very reasonable price, perhaps because the shipping cost was a bit high, but, considering the weight of the radio, and how well the unit was packed, I have to say the shipping was very reasonable. On receiving it, after carefully unpacking it and vacuuming out as many styrofoam bits as I could find, I assessed the condition. Cosmetically the case looked quite good, and the interior looked surprisingly good. I then gave it the acid test... try it out. I know, I know... there are going to be a few of you who will cringe at that, but, let me assure you I was watching the 5Y3 the whole time, and the plates stayed nice and black. I learned that trick a half century ago.

Anyway, the radio actually played pretty well considering it is unmolested. It even has the original "line cord antenna" as shown in the Rider schematic. On AM and SW it picks up quite a few stations. I live in Providence and it was receiving WOR New York in the daytime no problem, which is kind of a test I have to see if an AM radio is basically working OK.

FM is another kettle of fish. It seems to only be able to receive one station on the band, and that with a great deal of distortion. I have tested all the tubes and found only 2 weak ones. I have laid in replacements for those. I have also bought replacements for every capacitor in the radio. A few of the paper ones look "iffy"... and I may as well do the lot... the electrolytics I replace as a matter of course on a radio this age. I laid in micas for the tiny values, but will only replace them if all else fails, they usually stay pretty well. All the resistors appear fine... we will see after I replace the caps what happens.

Wish me luck, this should be fun !

[morzh]

As an EE to an EE - change all paper caps.

[codefox1]

Best! Probably need to shut it down, replace all capacitors (electrolytic and 'paper' types,) as they are certainly faulty or nealy so. Want to do a revamp, I would also replace carbon resistors which have long ago drifted way out of tolerence or thermally challenged. Then there is corrosion which of course contributes much to erratic behavior, and my favorite is Deoxit, but I don't work there or anywhere else anymore.

Sub a pair of ten cent diodes for the rectifier if you need to rectify the problem further.

[Mondial]

Hi Mike, and welcome to the forum. I have a 48-482 and have been working on restoration of mine on and off for some time. I think you will find that you will also will have to replace many off tolerance resistors.

One resistor in particular that may be causing your low FM sensitivity is R502, which is the plate load resistor of the 7W7 FM RF amp tube. This 33K resistor dissipates more than the rated wattage in circuit and invariably rises in value. It was completely open in my set and prevented the RF stage from operating, resulting in low sensitivity.

If you are going to change paper caps, check and replace off tolerance resistors at the same time and save some extra work.

[mikethedruid]

Thanks for the tips. Mondial, I checked r502 in circuit, and it is reading 47K instead of 33K, and may well be part of the problem. I also notice 2 paper caps in this same area of the radio, in that sub chassis with the tuning condensers on top and the FM switch underneath, which blocks access to a lot of the circuitry underneath. Is there any trick to accessing these ? I notice the sub chassis is attached with 3 screws. Can these be removed, and make the underside serviceable, or is this a horrible idea ? Should I just do my best to "build a ship in a bottle?" I also see that removing this might be a big problem considering the dial cord looks like a pain to restring. Any advice on this from those who have been down this road would be helpful

[klondike98]

Mike, I don't recall taking that assembly out. Checking my notes and photos the only disassembly I noted was taking the pushbutton tuning coils out, but I didn't have to unsolder anything:

[Image: https://dl.dropboxusercontent.com/u/5462..._recap.jpg]

[mikethedruid]

Thanks !.. yeah... that gives access to a lot.

[mikethedruid]

All the paper caps age replaced except 2 under the band switch that I really couldn't get at. All the electrolytics are replaced. On the paper caps I generally went next value up where I could not get the originals. Turned the set on... AM and SW work pretty well, maybe too well now... some squealing and regeneration on AM, and SW booms in with just the built in antenna. Realignment will be in order a bit perhaps. Fm is still problematic, picking up just the one station it did before I began work... so.. on with the hunt... more later.

[morzh]

Well, if the caps are interstage the next one up is OK, or even twice the value in many cases.
If it is a decoupling cap from B+ to GND, the more the better (within reason of course).

[mikethedruid]

well, I replaced r502, which was reading 47K when it should have been 33K. I also replaced the 7F8 and 7B6. AM and SW now work quite well, and now on FM, I am picking up 5 stations, weakly, but there.. so.. things are getting better. Now, R502 is down underneath the rotary switch that cuts the tuning from AM to FM, so that was sort of a "ship in a bottle" adventure.

[mikethedruid]

Had a day of frustration today. I began to chase little things under the chassis. For one thing the bass control was not working, and there was more of an AC hum than any newly recapped radio should have, so I began to poke around. Soon I found the problems, and began to correct them, or so I thought. When I fired the radio up again... nothing... just a hum. I began to trace circuits visually, and was surprised to find that my Rider's schematic shows a 6SQ7 where my radio has a 7B6, and on the inside sticker of my radio you can see where they blacked over the old number and printed 7B6 below it. Also, the 7B6 is oriented exactly 180 degrees out from the 6SQ7 in the Rider manual. well, needless to say this led to a WHOLE lot more circuit tracing, and consulting the RCA receiving tube manual. found that, although the tubes were different and oriented differently, I had put the right caps to the right places since I had done it all by eye in the first place. Still, checked and rechecked things with no luck. Finally pulled out my signal genrator and began to use it. soon found the problem. One of the loctal tubes had come loose in my turning the chassis over and back. well... having done all the triple checking, I am now pretty well confident that the radio is close. AM and SW are working VERY well now on just the built in antennas, and the sound is GREAT but FM is still a devil. I get 2 FM stations weakly. and just a hint of a few others, but nothing really distinguishable. So the hunt continues...

[klondike98]

Yep, 7B6 was the tube that actually went into the radios...not sure why the schematic wasn't updated. My trouble shooting skills don't go much beyond tracing the circuit for obvious problems and following the Service Bulletin procedures, but if AM & SW are playing the problem must be in the FM circuit. Don't know if you have the Service Bulletin for this model or not so I've put it online at https://dl.dropboxusercontent.com/u/5462...48-482.pdf

Check out the trouble shooting sections, hope that helps.

[mikethedruid]

Thanks a lot, Bob. The service bulletin you listed is almost exactly the same as the Rider listing, right down to the illustrations. Yours seems a bit clearer than the copy of the Rider listing I have, so it will be quite useful. I will be looking some more, and going through the procedures outlined in the bulletin.

[Mondial]

Mike, at his point you probably need to do a full alignment. The 48-482 uses an oscillating quadrature detector for FM (FM1000 tube), and if it is not adjusted exactly right the FM will sound terrible. The IF amps are common to both AM and FM, so aside from the alignment, the tubes and associated circuitry is probably ok since your AM and SW reception is good.

Try going through the Philco alignment procedure using the loading resistor, but I had better luck using a sweep generator for best symmetrical bandpass of the IF. Also it is important to set the free running freq of the quad detector ( primary of transformer Z300)at exactly 9.1 MHz with no signal, then with FM modulated signal adjust secondary of transformer for best linearity of the demodulation curve, centered on the IF bandpass.

Alignment made a tremendous difference in the FM performance when I did it on my 48-482.

[tom.seeger]

What are you using for an antenna Mike? A lot of the early FM radios needed a decent antenna for clear reception. At my location I need at least an indoor dipole behind any FM radio or all I get is weak distorted reception.