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 Post subject: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 8:18 pm 
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Hi, I am working on a Silvertone 7134 table model radio. The radio will not oscillate. It does have radio white noise. There is mouse damage on the oscillator coil as in the photo. Under a magnifying glass, I could see copper wiring where the mouse bit. I have other oscillators as a possible replacement from my stock. Which one should I use? options: 1, 2, 3, 4, 5, 6 as in photo. I am leaning toward #2.

Silvertone schematic:
http://www.nostalgiaair.org/pagesbymode ... 017696.pdf

The schematic shows this oscillator as L2. I measured for resistance- the result was 1 (open).
All the IF cans and the antenna loop had good resistance measurements.

This is all kind of new to me. Any help is appreciated.

Joe


Attachments:
silvertone 7134 mouse damage.jpg
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oscillator choices.jpg
oscillator choices.jpg [ 345.49 KiB | Viewed 875 times ]
Miller oscillator hook up chart.jpg
Miller oscillator hook up chart.jpg [ 250.1 KiB | Viewed 875 times ]
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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 9:13 pm 
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Hi Joe

Those marked RF or Antenna coil will not work as an oscillator coil. Best to use an oscillator coil with center adjustment slug. This will make it usable in most radios.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 9:17 pm 
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Thanks for info. How can you tell the difference between oscillator coil and antenna coil? I have many different coils in my stash from a radio collectors hoard. The #3 coil could be an oscillator coil.


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 9:23 pm 
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That can be hard to do. An oscillator coil will have fewer turns of wire than Ant or RF coil. The oscillator operates on a higher frequency.

Do you have one marked 9495C or 9496C?

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 9:33 pm 
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so far, I do not have one marked 9495C or 9496C. I will need to check my hoard. I suppose I could clip in the #3 coil and try it. I looks like it has wire turns like the original.


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 9:35 pm 
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https://www.tubesandmore.com/products/c ... oscillator

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Wed 01, 2020 10:10 pm 
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Here is one that I think may work in new photo. It does say osc coil. the only question is the box says 5.3 to 16.5 mc. do they really mean kc? would it be ok to drill a hole in chassis to mount this to where the adjustment part pokes out of chassis?


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 12:14 am 
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That one is for shortwave.

The one fifties mentioned will work.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 12:24 am 
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Try #3 before doing anything else. It looks like the same configuration as your original. Will need to figure out which terminal is which. Note that the section below the tap usually has a lower resistance than the section above the tap, when you are installing it.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 4:27 am 
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Any chance you might repair the old coil?

Did you check the windings for continuity and find one open?

Broken leads can often be spliced. If the outer layer of a coil is damaged, you might be able to splice-in some new wire and jumble-wind a few turns back on there.

Too late now for this set, but it's a good policy to check all of the coils and windings before doing much else to a set.

Ted


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 4:56 am 
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+1 on trying to splice, trying to sort one at the moment that's been chomped.

Marc


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 5:09 am 
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I have taken resistance readings on the white coil #3 as in photo in original post. The resistance between the lugs on the same side had 2.8 ohms. The resistance between the lone lug and the lug on the on the corner read 1.0 ohms. the resistance between the far lugs was 2.1 ohms. I am not sure how to hook this up.

fifties, I have seen this osc on Antique Electronic Supply before when I attempted to replace the ocs coil on my Montgomary-Ward radio. It had a similar mouse bite. The spec sheet on the Coil - Miniature adjustable coil, 70, oscillator says it has a primary and secondary. So, I did not fix my M-W radio because the spec sheet did not conform to the schematic on the radio. This is exactly the same situation with this Silvertone. The schematic shows a coil only--no primary or secondary. I am confused. Am I missing something here? I have read a lot in books about osc coils.

Usually Lurking, I have tried to solder those small wires on a meter- it broke moments after the solder. I do not want to do that. Besides, I just pulled out the original osc from the chassis. When I first looked at this radio, I did not notice the mouse damage. I am fixing this radio for someone else. Also, in my original post I said: The schematic shows this oscillator as L2. I measured for resistance- the result was 1 (open).

Thanks for info,

Joe


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 5:47 am 
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roguethistle wrote:

fifties, I have seen this osc on Antique Electronic Supply before when I attempted to replace the ocs coil on my Montgomary-Ward radio. It had a similar mouse bite. The spec sheet on the Coil - Miniature adjustable coil, 70, oscillator says it has a primary and secondary. So, I did not fix my M-W radio because the spec sheet did not conform to the schematic on the radio. This is exactly the same situation with this Silvertone. The schematic shows a coil only--no primary or secondary. I am confused. Am I missing something here? I have read a lot in books about osc coils.


Not rocket science, my friend. There's a lotta latitude on these consumer grade items. I recommended that coil because I used one when rebuilding a partially stripped chassis of a Federal 1040 I got on eBay for cheap.

The print that you posted a link to shows a single coil, tapped in about the center.

The diagram of this unit,

Image

Shows two coils. You only need the one that has the tap, so you would connect to terminals 1, 2, and 3. As Norm pointed out, you want an adjustable core, so the coil can be set to oscillate at the correct frequency. I'm reasonably sure this will work for both this radio, and the other one you mentioned.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 9:57 pm 
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fifties, thanks for the info. Yes I agree this stuff is not rocket science. I have restored over fifty radios and radio test equipment. I have used much creativity in that process. Yet much of electronics is not readily apparent for the novice like me. I will order 2 maybe 3 of the coils from Antique Electronic Supply as I have many more of these radios to repair. I am certain some of my radios in que have mouse damage.

I did hook up the white coil #3 per photo the way I thought it would work given the prior resistance readings in my previous post. The radio did not oscillate. Who knows, that coil could be from a TV set for all I know.

Joe


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Thu 02, 2020 11:18 pm 
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roguethistle wrote:
I have restored over fifty radios and radio test equipment.

...the novice like me.

Umm, somehow I can't quite fit these two sentences together... :wink:

roguethistle wrote:
I did hook up the white coil #3 per photo the way I thought it would work given the prior resistance readings in my previous post. The radio did not oscillate. Who knows, that coil could be from a TV set for all I know.


Exactly. Never hurts to try, but unless you have an RLC bridge or a Chinese inductance/capacitance digital meter, AND the inductance value of the osc coil per the schematic or service info, the only reasonably sure bet would be another osc coil, either from another AM radio, or a universal replacement, such as AES sells.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Fri 03, 2020 11:27 pm 
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fifties, thanks for your help and your compliment. I grade myself pretty hard sometimes. I went ahead and ordered 3 osc coils from AES. I should have them early next week. I will post how it works out.

Joe


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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Sat 04, 2020 3:10 pm 
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Fifties is spot on - to know which coil in your stash might work you would need to measure the reactances of the coils in your stash.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Sat 04, 2020 3:47 pm 
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As many know, oscillator problems can be some of the worst!!! I recently took on finishing a repair for the late Stan Saeger... a similar Silvertone. There are 2 diagrams for it, but neither agrees with the chassis as wired... Stan replaced the open oscillator coil and it wouldn't take off... I ohmed it out and rewired... dial is way off.. pulled about 3 feet of wire off and it's close, but wow, do I have repeats!!! Time to drag out the scope and see what is actually going on.
I, as many, will be most interested in the final outcome and what coil actually worked. My last effort may be to rewire the oscillator completely just to get it working properly, but that will throw a monkey wrench at the next guy that repairs it.
Keep us posted how you make out!!! Good luck!!!!

Jim

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Sat 04, 2020 9:39 pm 
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philcophanatic wrote:
My last effort may be to rewire the oscillator completely just to get it working properly, but that will throw a monkey wrench at the next guy that repairs it.


Easy solution for that. Simply tape a note inside the cabinet detailing your osc coil repair, or any other circuit deviation.

Be sure to do the rewind in the same direction as the original.

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 Post subject: Re: Which oscillator should I use?
PostPosted: Apr Tue 07, 2020 1:27 am 
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ok, I got the part from AES today. I installed it according to middle diagram and still no osc. I turned the allen wrench adjustment about 1 full turn and listened after each 1/4 turn. No osc. Is there any trick to this? I know somewhere on the ARF is info on aligning this osc from AES. I have not searched yet.

Joe


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