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"Sun testing" a GE 515-F radio chassis

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"Sun testing" a GE 515-F radio chassis Empty "Sun testing" a GE 515-F radio chassis

Post by Wildcat445 on Mon Oct 15, 2012 9:58 pm

My dear wife bought this GE 515-F clock radio at an antique store because she thought it was "cute". Paid huge money for it ($45.00). It was supposed to have been "completely restored", whatever that means. It IS in very good condition, appearance wise. I put it on my bench, and, sure enough, it did not work. In fact, it made no sound whatsoever from the speaker. MAYBE a slight hum, but that was mostly my imagination. All the tubes light. This model has that silly dip-soldered chassis that I have been avoiding like the plague, per earlier stories that I had been told. B+ appears to be okay. I found that there were some really loose connections on the tube sockets, so I squeezed all the tube socket connections with needle nosed pliers and got oscillator hash from the speaker. I moved the dial, and all the stations that this radio will receive is a short wave station with some preacher on it! True story! I am not on drugs. Actually, it picks this shortwave station up on two seperate places on the dial, about 1400 khz and about 900khz. Absolutely no AM stations are received anywhere on the dial. The lower end of the dial under about 700 khz motorboats and it is dead from 700 to 900khz, then I get oscillator hash again above that. And the aforementioned shortwave stations. Weird.

In fairness, I have had this radio for almost three years. I have had it "sun testing" for all that time. For those of you not familiar with sun testing, this is done on the end of my radio bench where the sun shines in from the window. Chassis that cause me grief are deposited on the end of the bench to sun test while I get the inspiration to fix them. I have two chassis currently occupying this place of "honor". This GE chassis and an inverted bakelite Zenith chassis. I ignore them until my conscience bothers me, I work on them for a couple hours or until I get annoyed, then back on the end of the bench they go. I had a Philco 116-B sun testing for almost 15 years until I got the parts necesary to fix it.

I have used VTVM's, a scope, signal tracer, signal generator, frequency counter and most of the other equipment that I own and really know nothing more than I did on what is wrong with this PITA than I did three years ago. I am convinced at this point that it has two major problems. The first is that the first IF can will not peak. By that I mean that I can peak it, and then it changes. I know. That is impossible. Second is that the oscillator trimmer on the tuning condenser has to be turned with the screw almost falling out to peak at 1620khz per the alignment instructions. And the setting on it changes, too. Again, impossible. I feed the output of my tape player thru the signal generator and listen to it on the radio. It will work well for 30 minutes or so, then lose volume. The settings on that IF can has changed. I move the tuning slug and get my audio back. Then it goes away. I can hook the signal generator to an antenna connection and get the audio of the tape player thru the radio. Never once have I heard an AM radio station. This radio should work. I suspected silver mica disease, but I don't get any positive voltage on grids like I would expect with SMD. When the oscillator trimmer changes settings, I have to screw the screw in as tight as it will go to peak the trimmer, but only sometimes. This radio has an extreme alignment problem, but I am at a loss as to why. And why will these IF transformers pass a signal at shortwave frequencies? How does the tuning cap tune to these frequencies? The antenna and oscillator coils appear original to the chassis. I suspected that someone who had "restored" the radio may have hacked something. I have not ruled this out yet, but what?

This chassis has been recapped. I have subbed the tubes ad nauseum. I have ordered an IF transformer to replace the one that I can't peak. I have re-checked the antenna and oscillator coils, and they check good. I checked the tuning capacitor, and it is not shorted with no plates rubbing that I can see. I used a magnifying class to aid in this. I am overlooking something simple. This is an AA5 for pity's sake, not a 30 tube Scott. There ain't that much to go wrong.

The frau would like me to get "her" radio back to her. She has forgotten how it looks. I want to get this piece of junk off my bench, and get my self-respect back. I implore your advice.

Thanks.

WC




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Post by Wildcat445 on Mon Oct 15, 2012 10:09 pm

I misspoke slightly. I should have asked why the tuning cap can tune to shortwave frequencies. My thinking is that the oscillator is running at the wrong frequency. When you work on a multi-band chassis, the oscillator frequency changes so you can tune to different bands, but the IF frequency does not. So, is it fair to deduct that, for some reason as yet unkown, that the oscillator is running at such a frequency to make this little GE a shortwave radio and not AM? Why?

Regards.

WC

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Post by Resistance is Futile on Mon Oct 15, 2012 10:44 pm

What do you mean by oscillator Hash?
Just white noise?
Does it squeal?
I think your right the oscillator is drifting.
One big culprit is the band switch. Another is leaky screen bypass cap.
Sounds like someone played with twiddling sticks too much.
You are going to have to take it one step at a time.
You may have components that are drifting in value with Heat. Resistors are notorious.
I would re-solder every connection and joint first.
It may be antenna connections. Try shorting the antenna and see if the ghost SW stations go away.
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Post by Wildcat445 on Tue Oct 16, 2012 4:14 pm

Thanks, Cliff. There is no band switch. This is just a simple, little GE clock radio. Should have a sign on the back "No user servicable parts inside"!.

I really don't have a squeal per se. The only strange noises it makes is at the low end of the dial. It motorboats. Then dead in the middle of the dial. Then white noise (oscillator hash) on the upper end of the dial. The oscillator is working when the tuning cap is in the "dead zone" of the dial, confirmed by negative voltage on the grid of the converter tube and by a corresponding squeal in another radio. Looking at the general condition of this chassis, it is in such great condition that I have a hard time confirming that anything has been hacked. The chassis has been totally recapped. The work was done neatly. I have re-soldered and/or heated every solder joint. I am beginning to wonder about the connections involved with the dip-solder portion of the chassis. I have run the wiring, per the schematic, several times, and have found nothing amiss. If I short the antenna, the ghost stations go away. But I have NEVER heard a hint of any AM station from this radio. Only the preacher on the SW station. I have confirmed that it is, indeed, a short wave station, since I can listen to the station on my Philco 116-B ( on SW) and the little AA5 at the same time! Strange.

I read a thread on a similiar problem awhile back, and the best advice given in that incident was to change all the resistors, capacitors, and micas having anything to do with the converter/oscillator stage. I may do that out of desperation and see what happens. I don't have any better ideas at this point. There has got to be a problem in that area to cause the oscillator to drift and to run at too high a frequency, making this AM radio into a shortwave set.

I have taken this thing a step at a time, and (I thought) checked every component thoroughly. Obviously, I am overlooking something. Probably something simple. One of those "oh, $hi*" moments.

Thanks and regards.

WC


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Post by Dr. Radio on Wed Oct 17, 2012 6:26 pm

Wildcat,

I believe this model uses the smaller IF cans that have the moveable iron cores as opposed to the earlier ones where they contain variable capacitors accessed from the top of the can only. I've found some radios where they have the "silver mica disease" style cans, but yet there was no silver migration, just oxidation causing the radio and me grief--the little contact pads inside would intermittently go "intermittent" as the pressure against the silver mica wafer was not that great and time takes its toll--poor connection.

I'm not saying that's your problem, just something to reflect on for those "tough dog" projects.

If I were you, I'd take and ohm meter and check from each tube socket pin connection to it's corresponding "dipped" connection to make sure nothing is open or high resistance.

If the capacitor in the oscillator area is one of those wonderful "Micamold" square jobber's with the domino dots, it wouldn't hurt to replace it. GE put some pretty cheap stuff in there mass produced radios.

How's the variable capacitor look? Rubber mounts okay? Trimmer screws messed up?

Just some thoughts.
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Post by Wildcat445 on Wed Oct 17, 2012 7:02 pm

Thanks, Doc. I am waiting for the new IF transformer and will go from there. Your idea to check the dip soldered connections is a good one, so I can do that while I wait. There is a Micamold cap in the oscillator circuit, so I will change it, just for grins. The tining cap and its mountings seem okay and the trimmer screws still work, inspite of my having manipulated them many times. The thing that really throws me for a loop is the high frequency that the oscillator is running at and why the alignment changes, both oscillator and the first IF. THAT is really strange. I guess I could scope the oscillator in a radio that is working well and then this one and compare the two. I am not sure what to look for nor what it would tell me if I saw it!

Thanks for your input everyone, and I will keep you posted.

Regards.

WC

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Post by stromberg6 on Sun Dec 02, 2012 8:00 pm

Is the "F" the red one?

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Post by Wildcat445 on Mon Dec 03, 2012 1:39 pm

Yes it is. In spite of my best efforts, the problem with this radio remains elusive. I have changed both IF transformers, and they peak okay now. I still have only one station that I can receive. A shortwave station with a preacher. Absolutely no AM stations, any place on the dial. This radio is currently doing an extended "sun test" on my bench at home while I spend the winter in warmer climate. I have done all I know to do. Something is running at a wild frequency, likely in the oscillator circuit. Why do I receive a shortwave station and only one? When I get back home, I guess I will break out the scope. Seems like lots of trouble for a clock radio, but curiosity has gotten the best of me. I must be overlooking something simple. There are not that many parts in the radio that can fail.

I cannot overlook the possiblility that prior servicing introduced a fault as yet undetected. Looking at this from a fresh prospective may reveal a clue, hopefully.

Thanks for your interest

WC

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Post by Bill Cahill on Mon Dec 03, 2012 4:06 pm

Bad mica caps in osc. circuit can also cause problems like this.
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Post by Dr. Radio on Mon Dec 03, 2012 9:06 pm

Actually I believe the "F" was GE's nomenclature for miniature tube circuit, or a mix of tubes that contain the 7 pin miniature tubes.

The number itself, is the color of the cabinet.

Be sure to let us know what you find. I've been pondering this one as well.....
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Post by Guest on Mon Dec 03, 2012 10:17 pm

I think you're right about the "F." I have a GE 515 and it has a mix of miniature and octal tubes.

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Post by Guest on Mon Dec 03, 2012 10:36 pm

The dip soldered boards can be a pain. A lot of the older equipment that I maintain at work is of such construction. the best way to eliminate such boards' trace microfractures is to flux the traces and reflow all of the traces. The etching process makes the traces brittle and the solder usually eliminates any intermittent or open traces. The feedthrough components subject to stress should be fluxed and reflowed also. I then clean the work with toothbrush, 91% isopropyl alcohol and blot with paper towels. I have found this procedure to be far less annoying than chasing down multiple intermittent opens.

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