Another project - Philco Tropic 42-788
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Well, it's alive. Sort of.
[Image: http://www.philcoradio.com/images/phorum...88_043.jpg]
It turns out that the audio output transformer from the 53-960 parts chassis I have was a closer match than the transformer from the 46-1226 (12K input impedance vs. 9K; the original was 12K), so I used the 53-960 transformer after testing and confirming that it was OK.
I then had to borrow a speaker from my (as yet unrestored) 41-788. I have an original speaker for this 42-788, but the cone is destroyed.
So...
I hooked up the 41-788 speaker, crossed my fingers, and fired up the 42-788...
Soon, it was producing the typical buzzing and static heard on the AM band.
Only...no AM signals...not even my SSTRAN!
SW 1 likewise appears to be dead; it has the static and buzzing but is picking up no signals.
I'm not sure about SW 2 as it is not yet evening, but it appears to be picking up some faint signals.
SW 3 is fine; I had no trouble picking up some activity on the 19m band.
I turned the band switch to all of the positions but did not try tuning the spread bands on the right side of the dial as I have not yet installed the needed rubber coupler between the tuning shaft and the shaft which runs the permeability tuner for those five spread bands.
At least I know the set has some life and does not appear to be miswired in any way. Whew!
So now comes the troubleshooting. I tested all of the tubes; the triode section of the 7J7 triode-heptode 1st detector tested slightly weak. I am wondering if it is enough to kill the oscillator on AM, or if I am looking at a coil issue? I would prefer it to be the former, but Murphy's Law being what it is, I wouldn't be surprised if it is the latter.
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Ron Ramirez
Ferdinand IN
Posts: 13,776
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No doubt about it - the AM oscillator coil is bad.
[Image: http://www.philcoradio.com/images/phorum...88_044.jpg]
The culprit is identified above with a red oval around it.
A closer look:
[Image: http://www.philcoradio.com/images/phorum...88_045.jpg]
The same coil is used for the AM band and for the second band, SW 1 (1.5 to 2.6 mc). It is a single tapped winding, and is open between the top of the coil and the tap. From the tap to the bottom of the coil, it is OK.
I am hoping that I can rewind this coil and make it work again.
Take a look at a partial schematic here (opens in new tab, click to enlarge if necessary depending on your monitor size). It shows the coil in question in red.
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Ron Ramirez
Ferdinand IN
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For what it's worth...
If you look at the partial schematic and compare it to the photos above, you may notice an extra mica capacitor and resistor. This was a production change:
[Image: http://www.philcoradio.com/images/phorum...88_rev.jpg]
This 42-788 has the changes. The 100 pF cap is new.
Of course, that won't fix an open winding on a coil. 
And Sam, if you see this...your 38-1XX 1st IF works well in this 42-788.  Even though the 38-1 has a 470 kc IF, the transformer tunes up fine at 455 kc.
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Ron Ramirez
Ferdinand IN
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hey ron
guess it`s true one mans junk is another mans treasure 
guess I will have to send more treasures your way
great work  hope you can rewind coil
sam
Some day, and that day may never come, I will call upon you to do a service for me. But until that day, accept this justice as a gift
mafiamen2
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City: Shepherdsville, KY
Hi Ron
You do good work replacing the rubber wire as you did with the 616 (by the way the 616 is working very good the remote, the phono and the radio. If I had a 6 volt solenoid it would reject by remote) sorry to hear about the coil (I have that with my 37-675) I tried to rewind it but did not work. That radio is bigger than I believed it to be. But you will get it going and you do good work.
Joe
Joe Bratcher near Louisville, KY
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Thanks, Joe; I really appreciate that. There were times while I was working on this 788 that I wondered which was harder to rewire: the 42-788 or the 41-616. Now that I think about it, I believe the 41-616 was definitely harder to do. I'm glad to hear you have it working well. Maybe sometime in the near future I can see a demo of it in action? 
Well, back to the 42-788.
I pulled the AM oscillator coil today, after taking careful notes as to how each of the wires hooked up.
[Image: http://www.philcoradio.com/images/phorum...88_046.jpg]
I had noticed what looked like a broken wire near terminal 1 of the coil before I removed it. After removal, it was readily apparent:
[Image: http://www.philcoradio.com/images/phorum...88_047.jpg]
It looks like something hit this coil, or scraped across it, causing a wire to break.
I carefully went over the coil with a heat gun to remove most of the old wax in order to see things better.
As it turned out, it was broken only one turn from the beginning. I unwound a few more turns just to see if the wire broke where it had been hit or scraped; the wire did not break, so those few turns were rewound and I soldered the end back to terminal 1.
After securing both the beginning and the end with hot glue, I went over each end of the coil with clear nail polish to hold the windings in place.
Afterward, it looked like this.
[Image: http://www.philcoradio.com/images/phorum...88_048.jpg]
I kept checking the coil with the ohms function of my DMM to make sure it was OK. I checked it over a final time after it was back in the radio.
[Image: http://www.philcoradio.com/images/phorum...88_049.jpg]
Now, it was time to try it out...
--
Ron Ramirez
Ferdinand IN
Posts: 13,776
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Success!
[Image: http://www.philcoradio.com/images/phorum...88_050.jpg]
I placed the chassis right side up, plugged the speaker back in, and fired it up again...
This time, it tuned in my SSTRAN and the music came in loud and clear.
I was really lucky with this one, I think. The loss of one turn on the oscillator coil made no difference, and I did not think that it would. It could have been a lot harder...
[Image: http://www.philcoradio.com/images/phorum...f/easy.jpg]
Whew!
Now I have to fix the dial pointer, install the dial pointer in the right side dial, find and install a rubber coupling for the right side tuning, and give the thing a complete alignment.
--
Ron Ramirez
Ferdinand IN
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Glad to see you were able to find and fix the break with out rewinding the whole coil. Good luck with the rest of the project looking good.( I would put claping icon hands here but I can't get them to transfer)
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Wow, a lucky break for you, indeed.
Never know whatcher gonna find under the wax…
Chuck
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No doubt about that!
I aligned the left side of bands today. I can't find the other rubber discs I bought when I had to perform a similar repair on my 42-761EZ's dial drive. I must have lost/misplaced them in our 2013 move. So, anyway...the right side dial, which is controlled by a separate tuning control which needs a piece of rubber just like the one I made for my 42-761EZ, will have to wait to be aligned until I get another rubber disc and cut it to fit.
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Ron Ramirez
Ferdinand IN
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So, armed with a new rubber washer, I proceeded to cut another coupling.
[Image: http://www.philcoradio.com/images/phorum...88_051.jpg]
[Image: http://www.philcoradio.com/images/phorum...88_052.jpg]
It was a pain to get the washer installed into the dial drive under the chassis, but I finally managed.
[Image: http://www.philcoradio.com/images/phorum...88_053.jpg]
I noticed when I removed the outer tuning shaft that it required some force to turn the shaft. So I removed the "C" retainer and pulled the shaft from the bushing. I cleaned it up, added some white lithium grease, and reinstalled into the bushing. Result: It turns very easily now. And with the new rubber coupling, the right side tuning works very well indeed.
I had to glue the pointer together, I shall see tomorrow once the glue dries how well it holds together. If it is OK, I will install the pointer and proceed to align the right side dial (five bands). Once that is done, the chassis will be complete.
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Ron Ramirez
Ferdinand IN
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Looking good. Kudos on the washer
Some day, and that day may never come, I will call upon you to do a service for me. But until that day, accept this justice as a gift
mafiamen2
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Thanks, Sam
Here is the repaired right side dial pointer:
[Image: http://www.philcoradio.com/images/phorum...88_054.jpg]
[Image: http://www.philcoradio.com/images/phorum...88_055.jpg]
The pointer broke at the point where the pointer wire is clamped to the aluminum frame. The wire bends over the top of the frame, and was unbroken. This helped make the repair possible.
So I installed the repaired pointer in the dial this morning.
[Image: http://www.philcoradio.com/images/phorum...88_056.jpg]
[Image: http://www.philcoradio.com/images/phorum...88_057.jpg]
After aligning the "spread-bands" on the right side of the radio, I listened to an African station in English in the 16m band for a little while before checking the other bands to confirm that all five are working (and they are).
That concludes the chassis work on this radio. Now the original speaker (which I have not yet shown in any pictures) needs to be reconed, and the cabinet is going to need a lot of help.
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Ron Ramirez
Ferdinand IN
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Great job a usual Ron. I really like the style of the radio. Are you doing the recone of the speaker?
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