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Found a 48-482 - Printable Version

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Found a 48-482 - zenith82 - 10-31-2005

Over the weekend, I picked up a 48-482 (the big 9-tuber with FM and SW). I've seen several of these before, but I haven't heard much in the way of their performance. I'd think with 9 tubes it would be fairly good; however, I did notice the original speaker looks a little on the small side for a table model this big.

Does anyone know how well these perform? Also, are there any problems this set was prone to other than the usual stuff? Of course on mine the dial cord has slipped and probably needs to be restrung. I looked at the diagram in Rider Vol. 18 and it doesn't look too bad (hopefully).

Tom

- Ron Ramirez - 10-31-2005

Having never worked on one of these, I can't speak firsthand on the 48-482's performance. However, I should mention it uses an FM 1000 second detector, and I have read that the FM detector section of these are problematic due to the tube and circuitry used.

- zenith82 - 10-31-2005

Thanks Ron. For some reason, even though these were expensive sets when new they don't seem very popular among collectors - possibly because of the amount of space they take up.

I looked at the schematic in Rider Vol 18 and I see the FM1000 circuitry you are talking about. I'd never heard of the problems associated with the FM1000, but then again I haven't serviced a Philco with FM before. Being a 1948 model, I wouldn't expect FM to be as good as it was say 5 years later.

Have a good evening!

Tom

- Terry Judkins - 11-01-2005

I have restored two of the 48-482s. Both are good performers. There was a steep learning curve to get the alignment right. Alignment is a long drawn out provedure with special jumpers. Follow it to the letter and the radio works fine. My big problem on the first one was a broken slug in the FM1000 detector coil. I used a slug from an old TV IF and after a lot of 'fanagleing' got it aligned. The IF and detector coil adjustment slugs are VERY fragile. Slightly loosen the lock nut on those that still have them before turning. That way you can tell when the adjustment has reached its limit or is stuck. Also squirt some WD40 (just a tiny amount) down the screw and let it soak before atempting to turn it.

I had hum in both radios until I added a filter choke. The field coil is in the negative lead and the drop across it provides the bias for the set. After a good read of RDH4, I decided to add the filter choke and the hum went away. Apparently the capacitive coupling from primary to secondary of the power transformer induces a loop current that causes the hum. The choke blocks the loop current.

I also added some filtering for the IF strip but not sure it was necessary.

The second 48-482 is the radio we listen to in the computer room. The speaker is small but sounds fine. My wife says it is the best sounding table radio we have. I am not much judge since my hearing stops at around 5KC.Icon_smile

There are LOTS of caps to replace with one special one under the RF deck. I did not have a ceramic to replace it but that would be best. I used two mylar caps in parallel and it worked.

I added a bit more feedback than original by paralleling a resistor around the feedback resistor.

Philco made a console that same year with the same chassis except it had a phase inverter and a pushpull 6V6 output.

- Chuck Schwark - 11-01-2005

Here's some circuit theory and info on the FM1000 from the Tube Manual section (Special Tubes) of my site, in case you guys have not seen it:

FM100 Characteristics