[Sean]

I am trying to finish up the alignment of one of these and am having trouble with getting the oscillator set to the proper frequencies at both ends of the dial. The instructions have you align at 88Mc and 105Mc. You adjust the oscillator coil at 88Mc and the trimmer cap at 105Mc. I find that I have to keep compressing the windings of the coil at 88Mc and keep withdrawing the trimmer cap at 105Mc. On each iteration I get closer but I have reached the extent of how close together I can get the windings of the coil. It seems that the oscillator should be running on the low side of the received signal (i.e. received frequency-I.F.). With this case I would need the oscillator to run at 78.9Mc for 88Mc and 95.9Mc for 105Mc. I have been checking the frequency of the oscillator with a coil of wire wrapped around the 7F8 tube and connected to my frequency counter. With the coil compressed I can get 78.9Mc with the dial set at 88Mc but when I set the dial to 105 I get about 93Mc from the oscillator. I spread the coil windings out as much as they would go and withdrew the trimmer cap as far as it would go to see if I could get the oscillator to run on the high side (received frequency+I.F.). At 105Mc it will oscillate at about 118Mc but at 88Mc it will only oscillate at about 88Mc so it does not seem that high side oscillating will work. Has anybody else had any problems with getting the FM dial to align on one of these sets? I know it isn't going to be completely accurate but I would think I could get it closer than 3Mc.

[Ron Ramirez]

I guess no one else has messed with one of these :

I've never owned one long enough to restore it. I do have one I have been trying to work on, off and on, during my move. I guess I shall find out for myself how the FM alignment is on this one.

[Terry Judkins]

I have restored three 48-482 radios. I made only very minor adjustments to the coils to tweak the dial calibration. Never had a problem. I used a
wooden stick with a ferrite taped on one end and a copper wire taped on the other to determine the direction to tweak. If the ferrite causes the tuning to be closer to correct then the coil needs to be closed up a bit. If the copper causes the tuning to be closer then spread the coil. The adjustment is very sensitive.

[Sean]

Well I did the alignment again this time by using over-the-air stations. I think it will be close enough for my use. There is a station at 88.1 that I listen to regularly and trying to get the dial aligned to pick it up as well as stuff at the upper end of the dial was kind of tricky. Now I just have to figure out why I am getting hum in the audio of weak AM and SW signals.

[DCASAZZA]

Hey Sean, I too have a 48-482 and use it every day. My FM seemed to track OK so I left it alone. The FM 1000 alignment procedure was different depending what write up I looked at so I pretty much left it alone too. I would be concerned about making a gross change to coils in the VHF band. Even a slight repositioning of seemingly benign components can cause a change.
New subject: I wound up making a change for the sake of AM/ SW performance by adding a .01uf cap to the cathode resistors (180 ohm) of the 2nd and 3rd IF amps. This greatly increased the sensitivity. I don't understand why they are missing from the factory but it sure helped. FM still seems OK for local and distant stations.
I like Terry's trick with the ferrite and copper to determint tuning direction.

[Don Lind]

Cathode bypass was the basis for endless engineering deliberations. Many of the factors could only be validated by laboratory measurements and would not be noticed by the user. Some of those factors are:

1. Stabilizing the IF strip to avoid oscillation
2. Grid matching for the transformer secondary
3. Bandwidth
4. Number of IF stages
5. Desired gain
6. Component end-of-life characteristics
7. Cost

They are all a trade off and determined to assure repeatability over a wide variety of components and tolerances. Often an improvement can be realized by optimizing an individual product.

[Sean]

I got the hum issue solved. It turned out that the 7F8 was modulating its local oscillator signal with hum. I replaced the tube and the problem went away. I'm guessing there is some heater-cathode leakage.

I am now buttoning up this set. I would like to reproduce the FM line aerial that was originally on these sets (Z100 on the schematic). I am assuming it is just a plate of thin sheet metal wrapped around the power cord. Is this correct? Does anybody have one of these sets that still has the original line aerial on it?

[Ron Ramirez]

I still have a 48-482 here that is partially finished.

I just checked it...yes, it has the FM antenna as you describe. There is one wire which protrudes from the chassis and is soldered to what looks like a large, long solder lug which is folded around the power cord on a piece of plastic molded into the cord for this purpose.

You could replicate this by putting some tape around the cord near the chassis to keep the metal piece from cutting into the insulation (most likely why Philco had a piece of plastic molded into the original cord). Then solder a solder lug to the wire, fold the lug around the tape, then add more tape to keep the lug in place?

[Sean]

Thanks Ron. I cut a piece of copper sheet about 1/4" wide and long enough to wrap around the power cord. I put a piece of fish paper between the copper and the cord and soldered a lead to the copper. It works pretty well.

I have another question that is somewhat related to the 48-482. I have a 2-page Philco advertisement from the Saturday Evening Post dated December 15, 1945. This ad shows a model 454 that looks exactly like the 48-482. It also has FM and SW. I would assume that the complete model would be a 46-454. I have looked around but cannot find any information on this set. I was curious if it is similar electrically to the 482. Do you have any information on such a model, Ron? The tag-line in the ad is kind of funny: "Ten Years Ahead of Four Years Ago!".

[Ron Ramirez]

Yes! Philco did announce a 46-454. It is listed in Philco Furniture History. However, it also states on the page for the 46-454 that it was "never produced."

A 46-454 is not listed in the Philco 1946/47 Home Radio Yearbook, a paperback volume containing schematic diagrams and service information for all 1946 and 1947 Philco models. So it appears it never made it beyond the design and planning stages...that is, until the 1948 season (June 1947) when it was finally issued as Model 48-482.

There are several 1946 Philco models listed in Furniture History that have the "never produced" note on them. Perhaps Philco was too ambitious in announcing a new line of radio models, and then found they were unable to produce all of the planned models, making most of them wait until the 1948 season? I honestly do not know.

I'd like to see that ad, if you could make a high-resolution scan of it and send to me. mr.philco AT yahoo DOT com