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1951 Admiral model 5E22 |
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1951 Admiral 5E22, purchased at a hamfest
in 2013 for 10 dollars.
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This came from a Hamfest in Sellersville,
PA. It was basically the only thing I bought that day. I didn't
notice it at the time, but there were some nasty scratches on
the gold trim and the cabinet.
Someone
had waxed the cabinet and didn't get all the wax out. This made
the scratches look worse. There was also some white paint on the
right side. It looked like maybe somebody banged it against a
door frame while carrying it. The knobs were pretty bad.Hey, it is 62 years old. I have more
scratches than that, and the radio is older than me! (barely)
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| Before and after. Eight
capacitors, two resistors and a vacuum tube were replaced. When I was
done... it didn't work! |
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Initially, the only sound the radio
made was a very loud hum, caused by bad filter
capacitors. After replacing the capacitors the humming
stopped but another problem arose. While the set was
warming up you could hear a radio station for about two
seconds, then it would be drowned out with static.
The static wasn't coming from
anything in the room, it seemed to be coming from
inside the radio!
This really had me scratching my head as I checked almost
everything, so I turned to those helpful guys on the
Radio Board.
Among other advice, they told me the set might have
Silver Mica Disease.
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"Silver Mica Disease"
or
"Electrolytic Electromigration" |
In the 1940s, '50s and '60s silver mica
capacitors were made by depositing a layer of silver onto a
sheet of mica. This is an excellent way to make a high quality
capacitor if the silver and mica are sealed in plastic.
However, if the silver is exposed to air it will oxidize. To make
matters worse, in an electric current the silver will migrate,
atom by atom across the mica, trying to reach the silver on the
other side. When it does it will vaporize in a tiny electric
arc. The process repeats over and over causing a steady static. |
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The capacitors in question are
inside the IF transformers.
DOH!! |
An IF "can" from a deceased radio
was substituted. The radio
came back to life. Dang, now I have to operate on the IF cans.
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One of the IF (Intermediate
Frequency) transformers.
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Two capacitors, one for each coil,
are contained on a single mica disk.
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| Notice the number 75 printed on the mica
disk. Each capacitor was rated at 75 Picofarad. Obviously the
value has changed, now that some of the sliver is missing. Now
is a good time to cut the mica wafer off and replace it with two
new capacitors, but I wanted to see if the radio would work the
way it was. |
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What is this stuff between the two
capacitors?
It's the silver. Silver Mica Disease!
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Each silver bridge was removed by
scraping it off with a small utility knife.
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| The case was polished with a
polishing wheel in an electric drill, mounted in a vise. Almost
every scratch was polished out. |
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| The radio now works very well. When it was
first turned on only a small amount of adjustment was needed.
There is enough silver left on the capacitors in the IF cans
that adding new mica capacitors isn't necessary. |
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| The knobs. |
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The gold colored steel inserts have
rusted.
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After cleaning and painting.
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I didn't know how I'd get the metal inserts
out without damaging them. The knobs looked pretty cruddy, so I
dropped them into a cup of hot water to soak before I took a
toothbrush to them. I noticed a bubble of air came out. There
was air behind the disks! I boiled a cup of water in the
microwave and dumped it onto the knobs. The expanding air
pressure popped both metal inserts out!
A day later it was off to an automotive
store with Andrea to find a matching gold color. She spotted it
right away. The metal disks were sanded and painted. AFTER I
painted them I noticed we had purchased a high temp engine
paint. The disks would have to "cure" at 200°F for 7 hours. No
problem, I put them on the radiator.
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The next day we raked leaves. Andrea stopped me in
the middle of raking and told me she had taken
the disks off the radiator and attached them to her boot. Then she
lifted her pants leg to show me.
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Why did she put them on her boot?
Did she lose her mind?
Then I saw the raised rims on the disks. Those disks came with the
boots! She does this crap to me all the time. |
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