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In my opinion I wouldn't bother messing with it as it is, find another chassis and make a good OEM chassis out of the two. This 90 is almost as bad as that Philco 643 battery set you had. The replacement speaker is probably acceptable to reuse, and would actually be an improvement over the old pie pan type.
The trouble with extensive modifications, if not out in out butchery, is that you really have no baseline to start from since the people who do theses sorts of things don't usually leave a schematic. As you say you can't be sure that whoever did the work did know what they were doing, some of these sets look like there were someone's weekend project so who knows whether they ever finished it and got it working properly, if at all.
Regards
Arran
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I would agree with Arran, Bob. If it were me I would wait for a original un-modified chassis to work on and use this chassis for parts, on the other hand the cabinet is in excellent condition. Philco 90's pop up every once in a while, although they seem to go for a pretty penny these days.
Jon
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Thanks for the advice. I just might have a lead on one...
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Looks like the modifications were done around the late 1940's. If so, this radio has existed modified longer than OEM... At least he didn't cut a hole in the cabinet for that eye tube, but just in the grill cloth.
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I decided to go ahead and pick up an unmodified chassis with a single 47 output. Here's my first look at it.
[Image: http://farm4.staticflickr.com/3799/91203...93cf_c.jpg]
[Image: http://farm8.staticflickr.com/7336/91180...5604_c.jpg]
Here's the modified one again for a comparison. You can see that components were removed - filter choke, bakelite blocks, capacitors and resistors.
[Image: http://farm8.staticflickr.com/7409/89704...3927_c.jpg]
I also have a matched set of knobs 
[Image: http://farm6.staticflickr.com/5479/91203...439b_c.jpg]
(This post was last modified: 06-23-2013, 03:09 PM by Bob Andersen.)
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Are they the same version? Look pretty different, but then I don't know what the differences between the versions are.
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Yes, they are actually the same version. They look so difference because of the heavy modifications done to the first one.
(This post was last modified: 06-23-2013, 08:37 PM by Bob Andersen.)
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Are you sure that the choke is missing from the butchered chassis, I see a transformer like thing with a black frame mounted bellow the power transformer? Or is that the output transformer?
Regards
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Neither. It's a 6.3VAC power transformer for the 6H6, 6F5 and eye tube that were added.
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Of course, I should have remembered, funny how it looks almost the same as the filter choke that should be in there. At least you can harvest it and use it to run a battery radio power supply.
Regards
Arran
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Heard that during WW2, radio repairers usually could not get exact replacement parts, and made do with whether they had on hand. This radio may be an example of that.
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The problem with the theory that the modifications were made during the war is that older types like 27s, 24s, 47s, etc were easier to get then the newer octal types. The hardest tubes to get during the war years were the 150 ma AC/DC tubes. Also if it were a case of just trying to keep the set running during a parts shortage why add a magic eye tube and socket?
Regards
Arran
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Way too heavy a mod for a simple repair. Whoever did that practically invented his own sch, not that there was a lot of rom for a fantasy there.....maybe someone got a bad chassis, gutted it and then let his imagination run....
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I don't really see any major obstacles here. I would guess that the original tube sockets were leaky and intermittent (often are for that vintage) and they were simply replaced with the more modern and reliable octal sockets and tubes. It's something I've done on junkers when I ran into repeated socket failures in a single radio.
Simply replace the sockets with the originals. Mark the wires as you take them off as to plate, G1, SG, or whatever and reconnect them to the replacement socket. As for the eye tube, just disconnect it.
A while back I worked on a Philco 19 junker that drove me nuts with sockets that would arc or just couldn't be made reliable; one by one these sockets were replaced with octals until the entire radio had nothing but octals. It works beautifully now and I would never get rid of it. (I know, I know- what about the tech in the future who services it? It's not my concern.) The chassis is marked for the new tube types.
Look at your 90 as an opportunity to better your skills in tube electronics ; swapping to different tubes isn't that difficult usually.
Pete AI2V
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It's not just a matter of some tube sockets being replaced. The power supply, detector and audio stages have been heavily modified. Between the hacked in 6.3 VAC filament transformer, rotting rubber wiring, replaced controls and dozen or more components that are simply gone, I just don't see any reason to deal with it. Especially since I already have another unmodified 90 chassis.
(This post was last modified: 06-27-2013, 10:28 AM by Bob Andersen.)
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