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City: Chicago, IL
Posts: 795
Threads: 42
Joined: Dec 2008
City: Chicago, IL
Here's what I found inside when I pulled the chassis.
Tube lineup - 80, 24A, 56, 24A, 35, 6H6, 6F5, 2A5, 6U5. Not exactly stock!
[Image: http://farm9.staticflickr.com/8541/89704...6ba0_c.jpg]
The most confusing modification was the 6H6 and 6F5 tubes because there's no 6.3 winding on the transformer secondary.
[Image: http://farm6.staticflickr.com/5443/89716...c025_c.jpg]
Nice blue Acrturus globe 56 where a 27 should be.
[Image: http://farm4.staticflickr.com/3817/89716...9fe0_c.jpg]
Finally, here's what I found underneath. What a mess! The IF and LO on the right seem original, but the rest has been radically altered. Two multi-section box caps, a filter choke, tapped bias resistor and most of the bakelite blocks are all gone  Instead, I have a few new caps one power resistor and a small 6.3 VAC filament transformer.
[Image: http://farm8.staticflickr.com/7409/89704...3927_c.jpg]
So what do you guys think ? it's already been suggested I just start looking for a new 90 chassis rather than attempt to restore this one.
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City: McPherson, KS
You may have the only 90 with an eye tube!!!! 
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Why not try and get it working as is. From the look of the under chassis work, it appears that the person who did the mods knew what he was doing. He used shielded cable for the audio wiring to the volume control, and the filament wiring of the 6 volt tubes is done properly with twisted pairs instead of using the chassis as a ground return.
So its not exactly original, but its performance will probably be better than a stock 90. The mods appear to be to only the audio section and the 2A5 will give better audio with less AC hum than the 47.
I kind of like working on a set like this, because without trying to maintain originality, you can make further mods without feeling guilty about messing up a pristine original.
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I kinda agree. You don 't stop it from being a tube radio and in a way, from being a 90 either....
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City: Minneapolis, MN
It looks clean and you could easily get rid of the six-volt tubes by using a 56 for both diodes of the 6H6, (See the use of the 76 in the 38-116 schematic), and by using the triode of a 55 for the 6F5.
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PS. There is a 2.5 V eye tube and if you don't want one, the 2nd detector is even easier.
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The thing is I'm not sure whoever modified it did know what they were doing. The original 6 mfd x2 plus filter choke has been replaced with a 40 mfd and 20 mfd x2. That's a lot of stress for an 80 rectifier tube. I'm not sure how they dealt with the two missing metal box caps that housed 5 caps in total.
Here's an unmodified 90 chassis showing the box caps, choke and bias power resistor.
[Image: http://mcclellans.com/images/Philco90/ChassisAfter.jpg]
(This post was last modified: 06-06-2013, 07:26 PM by Bob Andersen.)
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I would not be too concerned about 40 uF as a capacitive input filter on an 80 tube. It is electrically the same as a 5y3 and many later radios used it with a 40 uF input cap. You will be changing the cap anyway so if you feel more comfortable, replace it with a 20 uF. The other cap after the field winding can be much larger with no extra peak loading of the rectifier. What it looks like is the power supply of a late 40's model.
Most of the caps in the metal box were used as decoupling filters for the two 27 audio stages which are now eliminated. The 6F5 is taking the place of the two 27's and bias is now provided for the 6F5 by what looks like a few thousand ohm cathode resistor. There is a plate resistor and a coupling cap to the grid of the 2A5. Looks pretty much as it should be done.
You may assume that the mods were done many years ago by the vintage of the parts added, and that the radio worked properly at that time. I would not be at all reluctant to retain the mods and at least try it with proper precautions.
(This post was last modified: 06-06-2013, 07:56 PM by Mondial.)
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Take a shot at restoring the "Frankenphilco" as it is. At wosrst case you can always hunt down another chassis and resore it to original. In either case, you still have a better than usual cabinet. I kinda like the tuning eye also. Take care. Gary
"Don't pity the dead, pity the living, above all, those living without love."
Professor Albus Dumbledore
Gary - Westland Michigan
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If the original circuit used a 27 as a plate detector, the selectivity and sensitivity of the receiver are probably degraded by the 6H6 which loads the IF transformer much more than the original circuit. A diode detector makes sense only when you want AGC and/or the eye tube.
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The speaker is not original either. Who knows maybe this one is better.
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(This post was last modified: 06-06-2013, 11:06 PM by Bob Andersen.)
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80 tubes are inexpensive. I got some from eBay for a very moderate price.
A new eye of 6E5 type is 20 bucks new. And if you are willing to go to a Soviet 6E5S it may be even cheaper. And there are used tubes that may be as good as new.
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Oh I didn't mean to imply that I was in need of tubes as I have plenty of spares. I just thought I'd mention it. I was really hoping the eye tube had some life though as I don't have any others with the GE logo.
I just discovered something else. The lower left and right controls have been replaced with full round shafts. I'll have to file a flat on them if I'm going to use the Philco rosette knobs I dug up.
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