Silver mica disease and Crosley

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Silver mica disease and Crosley

Post by willy3486 on Mon Feb 17, 2014 8:52 pm

I have a question on the silver mica disease. I never ran across it years ago and when I got back into radios I ran across one that sounded like thunder at times. My question is I have a Crosley coloradio model 10-140 that I replaced the caps. I can now cut it on and it will play fine at first then after a couple of minutes it will loose volume and then nothing as there is no sound.  

So as far as the radio goes does it sound like Silver mica disease or should I look elsewhere? Its a AA5 radio.

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Re: Silver mica disease and Crosley

Post by Wildcat445 on Tue Feb 18, 2014 12:14 am

I would look elsewhere, Willy.  Do the tubes go out when it loses sound?  If they do, it is possible that there is an intermittent tube filament somewhere.  This radio has the tube filaments in series. I would replace all the tubes with a set known good.  Then operate the radio to be sure the problem is gone.  Then replace the tubes, one at a time, until the problem returns.  The last tube you replaced is the one with the intermittent filament.  Silver mica disease is pretty rare, in spite of all the hoopla about it.  It gives a crashing sound in the speaker, like lightning striking.  The sure-fire test for SMD is to check the tube grid following the IF transformer for positive voltage.  If there is any positive voltage on the grid, you need to suspect SMD.  SMD is the nastiest problem to deal with in a radio, even worse than tuner and dial re-stringing.  I always eliminate all other possibilities before I want to deal with SMD.  It might be a good idea to check you work again.  A bad solder joint could also give this symptom.  That's my guess.  Good luck.

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WC

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Re: Silver mica disease and Crosley

Post by willy3486 on Tue Feb 18, 2014 8:22 am

Thanks Wildcat. I have not run into SMD other than one time. I never saw it and had no idea it was even a issue back when I quit working on them around 92. Now I am into it I hear all this stuff about it. As far as the radio I do go out and swap the three main tubes used in the tuning area, 12ba6 ,12be6,12sq7 If my memory serves me right. I will double check the solder joints as well. It is a pain to get to some of the areas. I just picked this radio up Saturday so I haven't done much to it. I just was trying to figure out if SMD was the issue or not. But it plays for a few minutes then it is like the volume is turned off.

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Re: Silver mica disease and Crosley

Post by Dr. Radio on Tue Feb 18, 2014 9:40 pm

Willy,

Follow Wildcat's advice, but if you've covered all your bases, try my suggestions on IF "can" troubleshooting:

http://www.tuberadioforum.com/t3071-knight-kit-star-roamer-repair#22716
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Re: Silver mica disease and Crosley

Post by Ragwire on Fri Feb 21, 2014 1:02 am

You said you swapped the 12SQ7? I almost never find a good SQ7 unless it had been hardly used. The seem to like to short inside.
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Re: Silver mica disease and Crosley

Post by willy3486 on Fri Feb 21, 2014 1:21 pm

Here is the latest. I tinkered with it some this morning. I resoldered all joints I soldered and a few extra. I checked the filiments and tubes, nothing wrong from what I can tell. I also sprayed each socket with cleaner as some were corroded. That did help for a while then back to the old fading tricks. I also tried pushing down on the leads of the IF transformers. Nothing happened then. One thing I did find out is the second transformer will act like a reverb when it is acting up if you tap the side. You can hear a echo. So I am going out now again to the shop for a look at that transfomer. I am wondering if one of the coils in the IF transformer has a bad solder joint. I may also resolder all the connections to the transformer first. I am still a little rusty but it makes sense what I am finding out and reading here.

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Re: Silver mica disease and Crosley

Post by willy3486 on Fri Feb 21, 2014 2:50 pm

Latest from the Crosley. I went back out and turned it back on. It played but this time I couldn't get it to echo when I tapped it. I then went and resoldered every solder joint from the 1st IF transformer to the antenna. It still would play a few minutes the go to low sound. to the But when it acted up I noticed if I tapped the 100 ohm resistor tied into the 35w4 output to the filter caps it would then start to come in. So I went through and resoldered this resistor and anything close to it. I let it play for a few minutes and it seemed like it was playing longer. I left it playing in my workshop while I am eating lunch. I will report back later on if it is still playing when I go out there.

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Re: Silver mica disease and Crosley

Post by Bill Cahill on Fri Feb 21, 2014 4:46 pm

Cracked resistor being affected by heat??

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Re: Silver mica disease and Crosley

Post by Dr. Radio on Fri Feb 21, 2014 6:27 pm

Willy,

What you were experiencing (echos as you referred to it), is actually called "microphonics". This can be caused by a bad component, an element inside a tube or flaky connection.

If Bill is correct and you have had your 100 ohm filter surge resistor overheating, I would check your voltage readings. Excess current in the B+ line will cause excess power thru this resistor.

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Re: Silver mica disease and Crosley

Post by willy3486 on Fri Feb 21, 2014 8:51 pm

Dr. Radio wrote:What you were experiencing (echos as you referred to it), is actually called "microphonics".

I knew it was called something like that but I couldn't remember what it was called.

I checked the resistor Bill and it was fine. It wasn't overheating or getting hot it just has a bad solder joint. I had noticed when I was touching the IF transformers with a plastic tool that if I touched the resistor area the sound came back.  I went through and resoldered all the connections around the resistor. I noticed where the resistor was soldered to the tube that it looked like a bad solder joint as well as the other end. I wonder if these were prone to that or if there was something buggy going on the day it was made. The end that I suspect was bad I did not solder before it got to playing correctly. It reminds me of the old GE color TVs made in the late 70s that were prone to bad solder joints.

Well on to the radio. So I went ahead and put a new cord on it as the original was not the best. I then soldered a wire to the antenna board I had connected to it with a jumper. I sat it down on the bench and let let play. after an hour it was still playing. I just let it play and did some other work. So it played at least 4 to 5 hours with no issues. So I think this one is ready to go back together. I am going to repaint it tomorrow and put it together in the afternoon. So the last issue was the bad solder joint on the resistor. So thanks for all the help.

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Re: Silver mica disease and Crosley

Post by Guest on Sat Feb 22, 2014 4:55 pm

Glad you got it solved and let us know what you found. I picked up a little RCA AA5 the other day that someone had already re-capped and it does the same thing. I hope to get back to my farm in the next few days and spend some time on it

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Re: Silver mica disease and Crosley

Post by willy3486 on Sun Feb 23, 2014 12:02 am

Hopefully you can find it easy. This was a puzzling but easy fix. I had a bad run lately with radios but thats how it goes. So I am glad to get back to having luck fixing them. I got this from a lady who has a second hand store. She lets me know when she has radios. She has a really nice Zenith suitcase that is almost perfect but she is asking 125. But it may be worth it due to its condition.

This one was odd as when it acted up I couldn't trace a signal like I usually do. I wonder if the bad solder joint setup like a diode and dropped the voltage due to it. One time I was working in maintainence  in a factory we had a 120 plug in a test box that tested similar to a diode. The boxes were used to test hair clippers and all the oil allowed a sort to form through the hot and neutral on the socket. Good luck on the RCA. Anymore unless its something as interesting as this crosley I pass on radios unless they are RCA.


Here is the radio, it had latex pink paint and disney characters on it. I bet it was a young girls radio.

 


And the after. I used a heat gun to heat the latex then peeled it off with a razor blade scraper. The green color is not like the original color but it is like another crosley I have that I plan to restore and put next to this one. The color is off in the picture. My camera doesn't take the best picture. IT is more of a lime green color.



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Re: Silver mica disease and Crosley

Post by Guest on Sun Feb 23, 2014 10:28 am

Great before and after pictures, you did a great job!  Very Happy 

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Re: Silver mica disease and Crosley

Post by Wildcat445 on Sun Feb 23, 2014 12:36 pm

Nice job, Willy! It feels good when the "old radio curse" is finally lifted. Being in a slump like that is never fun. Where you can't do anything right. Been there, done that.

It is kinda amazing how wrong people who know what they are doing can be when diagnosing a radio via cyberspace.

Regards

WC

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Re: Silver mica disease and Crosley

Post by Dr. Radio on Sun Feb 23, 2014 3:11 pm

You should have left the Disney theme on it, listed it on eBay as "ultra rare Crosley Mickey Mouse Radio" with a buy-it-now of $1000!

Glad ya got it going!
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Re: Silver mica disease and Crosley

Post by willy3486 on Sun Feb 23, 2014 4:28 pm

Thanks folks. I hope my luck continues. I just got in a large box of parts from allied. I never ordered from them so I thought I would try. They have something called inventory overstock or something similar were they were selling stuff cheap. I was buying 100 of the 33 mf caps for like 10 bucks. They are name brand parts too. I also bought two transformers to make two battery sets power supplies like at
power supply

I want one that I can leave in my workbench and one I cane take anywhere.

My next project I plan to do is a old watterman scope. I picked it up a year or so at one of the Nashville meets. I have worn out all my other scopes and I could really use this one.

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Re: Silver mica disease and Crosley

Post by Bill Cahill on Sun Feb 23, 2014 9:11 pm

I'm cursed right now with two radios. The receiver of part of my 1947 three way combination Bendix, with a bad I F transformer in the radio, and, The radio part of my RCA Victor radio-tv combination. The fm died, then, the am died. That was two days before I ended up in the hospital last year. That is a sad story in itself, because I had both the tv, and, radio playing great.
NOT ANY MORE........

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Re: Silver mica disease and Crosley

Post by Ragwire on Sat Mar 01, 2014 7:45 pm

Very very nice Willy!
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What is Silver Mica Disease?

Post by skykng on Wed Mar 26, 2014 8:57 pm

Hi:  I'm new to this Forum but have been around the block a couple of times with old radios.  I read the above thread with interest and noticed that no one gave a shot at defining the mysterious silver mica disease.  I never knew what it was, or even heard it called that name until a few years ago when it hit me that I had run across many IF cans that I replaced along the way because of what turns out to be SMD.  My undertsanding of it is the very thin little slices of mica that separate the plates of the trimmer capacitors in some IF cans and fixed capacitors with induction tuning slugs in other IF cans deteriorate and break down to sputter leakage between the plates.  It sounds to me like a loose connection that randomly injects a scraping/rushing sound into otherwise good audio.  The radio plays OK, it just has this noise that more often is constant but random in volume, density, raspiness, crackling, high pitched scraping a coffee can half full of ball bearings across rough concrete.  You can spend a week trying to find it - but now that it has a name and everyone knows about it, you'll know it when you hear it and you can change out the IF can in no time.  Now, wasn't that easy?  If someone has a better/more correct definition or story about SMD, I'd sure enjoy reading about it. best,
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Re: Silver mica disease and Crosley

Post by Wildcat445 on Thu Mar 27, 2014 11:59 am

The problem with SMD is that it is massively over-diagnosed. It is still, in most cases, a fairly rare occurance. Zenith and Admiral sets of the early 1950's seem to be most infested with SMD. Any IF transformer with slug-tuned IF's can have it. The surest diagnosis is checking for positive voltage on the grid of the tube following the IF transformer in question. Not positive voltage, no SMD and vice versa. The noise SMD produces is caused by positive voltage spikes being fed into the tube.

Welcome to TRF, by the way. Glad to have you here. Jump right in, and post often.

Regards

WC

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Re: Silver mica disease and Crosley

Post by skykng on Thu Mar 27, 2014 1:24 pm

Thank you, Willy.......good tips! Looking forward to the TRF...............
best, steve
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Re: Silver mica disease and Crosley

Post by Dr. Radio on Fri Mar 28, 2014 9:05 pm

skykng wrote:Hi:  I'm new to this Forum but have been around the block a couple of times with old radios.  I read the above thread with interest and noticed that no one gave a shot at defining the mysterious silver mica disease.  I never knew what it was, or even heard it called that name until a few years ago when it hit me that I had run across many IF cans that I replaced along the way because of what turns out to be SMD.  My undertsanding of it is the very thin little slices of mica that separate the plates of the trimmer capacitors in some IF cans and fixed capacitors with induction tuning slugs in other IF cans deteriorate and break down to sputter leakage between the plates.  It sounds to me like a loose connection that randomly injects a scraping/rushing sound into otherwise good audio.  The radio plays OK, it just has this noise that more often is constant but random in volume, density, raspiness, crackling, high pitched scraping a coffee can half full of ball bearings across rough concrete.  You can spend a week trying to find it - but now that it has a name and everyone knows about it, you'll know it when you hear it and you can change out the IF can in no time.  Now, wasn't that easy?  If someone has a better/more correct definition or story about SMD, I'd sure enjoy reading about it. best,


Hi Steve, welcome to the forum.

There are actually (2) failure modes to the miniature IF transformers with the fixed capacitor design. One being the actual migration of the silver substrate that results in the 'horrific' "thunderstorm" sound in which you can do the positive grid trick test. The other being the intermittent contact of the corresponding connection tab to the silver substrate. The positive grid trick test will not work in this situation. This isn't so much of the "disease", but can be just as common as it intermittently "removes" the "C" part of the L-C combination circuit due to the high resistance created and you may encounter a radio station that "magically" moves 1000 miles away (great loss of volume and sensitivity very intermittently).

You can read about my investigation and thoughts in this thread:

http://www.tuberadioforum.com/t1915-step-by-step-restoration-ge-t-106c-let-s-go-for-it

Page 4 begins the adventure that is IF transformer repair.
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Re: Silver mica disease and Crosley

Post by Guest on Fri Mar 28, 2014 9:51 pm

you may encounter a radio station that "magically" moves 1000 miles away (great loss of volume and sensitivity very intermittently).


OK......now this I've seen more than a few times!

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Re: Silver mica disease and Crosley

Post by Bill Cahill on Fri Mar 28, 2014 11:14 pm

I have seen smd on many radios over the last fourty five years.

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