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Old 07-24-2017, 04:50 PM
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Philco 48-482 question

I was given a Philco 48-482 table radio recently. I typically don't restore tube radios, but given that this set has 3 IF stages for both AM and FM and a 7F8 dual-triode oscillator/mixer, it should be an extremely hot performer on the AM band. Can anyone confirm this?

Also, is the FM-1000 demod circuit a pain in the ass to align? When fully aligned, is the Philco a hot FM performer?

I ask because when I'm in the states, I'm in a pretty difficult location for adequate reception of the FM stations I'm interested in. No sense in restoring yet another tube radio/tuner that doesn't pull anything in that I care about...
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Old 07-26-2017, 09:06 AM
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Ben,

I had a 48-482 that I restored and used on my desk at work where reception is poor (especially AM). I had no problems pulling in FM stations and could pull in a lot of AM stations as well. The audio quality of FM isn't as good as some later FM sets (I used to have a Grundig on my desk that had great audio) but it's OK.

The FM-1000 detector can be a little finicky. Follow the alignment instructions carefully and you will be fine. I do remember after using the set for quite a while the FM quit. It turned out 47k resistor in the plate supply for the FM-1000 failed. I think this was a 1/2 watt unit originally and is dissipating at least that much. I replaced it with a 1 watt unit and didn't have a problem afterward.

There are about 30 paper and electrolytic capacitors in that radio so there will be a bit of work to get them all replaced. Some are also a bit difficult to get at. I eventually took mine off of my desk just to get a little more room. It is a big set.
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Old 07-26-2017, 09:45 AM
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I've got one. I need to recap it eventually. It still works decently on original caps (I've only given it a few minutes of run time to test it though), performance seemed good for a early post war set (most post war FM sets seem to have weak FM)...It was getting comparable reception to a modern set.

I almost recapped mine, but it's a bit tight under chassis, one of the paper caps serves as a coil form (which would have made me re-stuff that then all the other caps to be consistent), and it works which makes it's recap priority lower than other projects that don't work.
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Old 07-26-2017, 11:49 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Electronic M View Post
I've got one. I need to recap it eventually. It still works decently on original caps (I've only given it a few minutes of run time to test it though), performance seemed good for a early post war set (most post war FM sets seem to have weak FM)...It was getting comparable reception to a modern set.

I almost recapped mine, but it's a bit tight under chassis, one of the paper caps serves as a coil form (which would have made me re-stuff that then all the other caps to be consistent), and it works which makes it's recap priority lower than other projects that don't work.
I have one, as well! Mine needs a re-cap, FM is non-existant. FM1000 checks good. Philco referred to that circuit as a locked oscillator FM detector. It couldn't have been that good, they only used it for a year or two.
That thing was $150 in 1948! They seemed to sell a lot of them.
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Old 07-26-2017, 12:36 PM
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Quote:
Originally Posted by Electronic M View Post
I've got one. I need to recap it eventually. It still works decently on original caps (I've only given it a few minutes of run time to test it though), performance seemed good for a early post war set (most post war FM sets seem to have weak FM)...It was getting comparable reception to a modern set.

I almost recapped mine, but it's a bit tight under chassis, one of the paper caps serves as a coil form (which would have made me re-stuff that then all the other caps to be consistent), and it works which makes it's recap priority lower than other projects that don't work.
I've found most early postwar FM tuners to be piss poor performers. A bulk use the Hazeltine fremodyne which has the sensitivity of a potato...

Exceptions to the rule of terrible post-war FM performance are the GE XFM-1 (mediocre), the Edwards Fidelotuner (mediocre), and the Meissner 8C (phenomenal).

I'll move my Philco up the restoration queue.
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Old 07-26-2017, 12:41 PM
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Quote:
Originally Posted by dieseljeep View Post
I have one, as well! Mine needs a re-cap, FM is non-existant. FM1000 checks good. Philco referred to that circuit as a locked oscillator FM detector. It couldn't have been that good, they only used it for a year or two.
That thing was $150 in 1948! They seemed to sell a lot of them.
It's possible that the circuit was a poor performer, but a paper from the BBC showes it had average performance in some regards, but unparalleled AM rejection. Perhaps the FM-1000 tube was too expensive to manufacture? Or too difficult to get adequate alignment on an assembly line? Makes ya wonder in any case... the Philco 48-482 was a major seller.
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