Old capacitors in old radio

[mc]

I'm getting ready to overhaul a radio that dates from roughly 1954 and am
wondering which kinds of capacitors need replacing.

I know the electrolytics and wax-paper capacitors (with wax outer surfaces)
need replacing, and the mica and ceramic ones don't. (One of the
electrolytics has failed, which is what got me started on the project.)

What about the ones housed in plastic tubes (with a hard plastic surface)?
Are they wax and paper or are they plastic inside?

 

[msg]

I'm getting ready to overhaul a radio that dates from roughly 1954 and am
wondering which kinds of capacitors need replacing.

I know the electrolytics and wax-paper capacitors (with wax outer surfaces)
need replacing, and the mica and ceramic ones don't. (One of the
electrolytics has failed, which is what got me started on the project.)

What about the ones housed in plastic tubes (with a hard plastic surface)?
Are they wax and paper or are they plastic inside?

I suggest investigating the performance of each stage in the radio
before replacing any capacitors; surprisingly, I have found that some
of the grungiest wax paper capacitors, if the wax is copious and
intact, have retained their characteristics more frequently than
ceramic disc and other types of the same age. Some old and well-built
electrolytics also are very long lived and may only need reforming
if not charged recently (use a variac).

Regards,

Michael

 

[Andy Cuffe]

I'm getting ready to overhaul a radio that dates from roughly 1954 and am
wondering which kinds of capacitors need replacing.

I know the electrolytics and wax-paper capacitors (with wax outer surfaces)
need replacing, and the mica and ceramic ones don't. (One of the
electrolytics has failed, which is what got me started on the project.)

What about the ones housed in plastic tubes (with a hard plastic surface)?
Are they wax and paper or are they plastic inside?

The ones in hard plastic tubes (usually black) are paper and need to
be replaced. The ones that are dipped in shiny (usually orange, or
brown) epoxy are usually ok. Also, the ones that look like hollow
tubes are ceramic and are usually ok. Anything else is suspect and
should be tested, or replaced if there's any doubt.
Andy Cuffe

[email protected]

 

[CJT]

The ones in hard plastic tubes (usually black) are paper and need to
be replaced. The ones that are dipped in shiny (usually orange, or
brown) epoxy are usually ok. Also, the ones that look like hollow
tubes are ceramic and are usually ok. Anything else is suspect and
should be tested, or replaced if there's any doubt.
Andy Cuffe

[email protected]

I don't understand why you think it necessary to replace the paper/wax
ones without testing. In my experience those can last a _long_ time.

 

[James Sweet]

I don't understand why you think it necessary to replace the paper/wax
ones without testing. In my experience those can last a _long_ time.

It's standard procedure. They already *have* lasted a LONG time. Ask any of
the experienced guys on rec.antiques.radio+phono and they'll tell you the
same thing. Skimping out on replacing a 10 cent capacitor can easily burn up
an expensive output tube or irreplaceable transformer. 70+ year old
paper/wax capacitors are simply not reliable and can't be depended on. Do
the job right and do it once, and the radio may well be playing for another
70 years.

 

[mc]

The ones in hard plastic tubes (usually black) are paper and need to
be replaced. The ones that are dipped in shiny (usually orange, or
brown) epoxy are usually ok. Also, the ones that look like hollow
tubes are ceramic and are usually ok. Anything else is suspect and
should be tested, or replaced if there's any doubt.
Andy Cuffe

Thanks, exactly what I needed to know!

 

[Ian Malcolm]

It's standard procedure. They already *have* lasted a LONG time. Ask any of
the experienced guys on rec.antiques.radio+phono and they'll tell you the
same thing. Skimping out on replacing a 10 cent capacitor can easily burn up
an expensive output tube or irreplaceable transformer. 70+ year old
paper/wax capacitors are simply not reliable and can't be depended on. Do
the job right and do it once, and the radio may well be playing for another
70 years.

Tin foil + waxed paper insulator, wrapped construction. I thought it
was overkill to replace them all at first, but then I remembered tin
whisker growth has taken out *many* far more recent AF117 transistors
and that is *TIN* foil in the caps. If they aren't shorted now, they
soon will be . . .

 

[CJT]

It's standard procedure. They already *have* lasted a LONG time. Ask any of
the experienced guys on rec.antiques.radio+phono and they'll tell you the
same thing. Skimping out on replacing a 10 cent capacitor can easily burn up
an expensive output tube or irreplaceable transformer. 70+ year old
paper/wax capacitors are simply not reliable and can't be depended on. Do
the job right and do it once, and the radio may well be playing for another
70 years.

The radio in question is about 54 years old. Post WWII.

 

[CJT]

Tin foil + waxed paper insulator, wrapped construction. I thought it
was overkill to replace them all at first, but then I remembered tin
whisker growth has taken out *many* far more recent AF117 transistors
and that is *TIN* foil in the caps. If they aren't shorted now, they
soon will be . . .

They'd have to be some pretty darn big whiskers. Transistors are on
a different scale.

 

[Ian Malcolm]

They'd have to be some pretty darn big whiskers. Transistors are on
a different scale.

Have you read NASA's tin whisker and their impact on satellite
reliability pages? <http://nepp.nasa.gov/whisker/>

Of specific interest is
<http://nepp.nasa.gov/whisker/background/index.htm#q5>
I quote:
"Whisker Length: Whiskers as long as a few millimeters are not uncommon
with some experimenters observing whiskers as long as 10 mm (400 mils)
in length."

And:
"tin whiskers can grow through conformal coating and once exposed can
then short to other tin whiskers or other exposed surfaces."

So it looks like they can be pretty darn long *and* grow through soft
plastics. Wax isn't going to stop them . . .

 

[Eeyore]

I don't understand why you think it necessary to replace the paper/wax
ones without testing.

Water absorbtion.

Graham

 

[Eeyore]

and that is *TIN* foil in the caps.

TIN ? Not aluminium ?

Graham

 

[Ian Malcolm]

Ian Malcolm wrote:




TIN ? Not aluminium ?

Graham

Well I remember (from about 30+ years ago, when I was an impoverished
hobbyist obtaining *nearly all* my components out of any ancient TVs,
radios gramaphones etc. I found dumped + a few treasured parts I'd
inherited from my Grandfather or been given by a few generous hams and
techs) dismantling a few waxed paper caps that were too damaged or dirty
or faulty to use. The leads were *SOLDERED* to the ends of the rolled
foils . I really doubt that over 60 years ago, leads could be soldered
reliably to thin *aluminium* foil.

I am not saying there weren't *any* Aluminium foil waxed paper caps with
leads spot-welded to the foils, but surely the common use of Aluminium
came in with the phenolic cases and phenolic impregnated dialectrics
followed by early polystyrene and Mylar film caps?

Remember Tin was a lot cheaper back then and Aluminium was still pretty
expensive and mostly used in the aircraft industry. I was also not
favourably impressed with the durability of 40's Aluminium. All the
light weight utensils I saw or handled from that period when I was a kid
suffered from serious 'tin worm' with tracks of corrosion often right
through the metal, yet aluminium utensils from more recent years that
are now just as old are usually still servicable or have failed with
localised pitting, not wriggly 'wormtracks'.

If you have any evidence to the contrary, I would be quite happy to be
corrected and extend my knowlage.

 

[Baron]

Well I remember (from about 30+ years ago, when I was an impoverished
hobbyist obtaining *nearly all* my components out of any ancient TVs,
radios gramaphones etc. I found dumped + a few treasured parts I'd
inherited from my Grandfather or been given by a few generous hams and
techs) dismantling a few waxed paper caps that were too damaged or
dirty
or faulty to use. The leads were *SOLDERED* to the ends of the rolled
foils . I really doubt that over 60 years ago, leads could be
soldered reliably to thin *aluminium* foil.

I am not saying there weren't *any* Aluminium foil waxed paper caps
with leads spot-welded to the foils, but surely the common use of
Aluminium came in with the phenolic cases and phenolic impregnated
dialectrics followed by early polystyrene and Mylar film caps?

Remember Tin was a lot cheaper back then and Aluminium was still
pretty
expensive and mostly used in the aircraft industry. I was also not
favourably impressed with the durability of 40's Aluminium. All the
light weight utensils I saw or handled from that period when I was a
kid suffered from serious 'tin worm' with tracks of corrosion often
right through the metal, yet aluminium utensils from more recent years
that are now just as old are usually still servicable or have failed
with localised pitting, not wriggly 'wormtracks'.

If you have any evidence to the contrary, I would be quite happy to be
corrected and extend my knowlage.

I too remember melting the wax from those old capacitors and
re-soldering the connecting wire after I had broken it from rough
handling. So I suspect that they were probably tin foil. I'm going
back nearly 50y. I'm 65 in Feb. Soldering irons like pokers !

 

[Michael A. Terrell]

The radio in question is about 54 years old. Post WWII.

So what? The paper used to make the capacitors was high in acid
content. As the caps age, they start to adsorb moisture which breaks
down the fibers and the dielectric develops leakage.

That will change the bias voltage on the grids, which cause the tubes
to conduct harder. That puts a heavier load on an already overworked
power transformer. A ot of those old radios were built for a lower line
voltage, which causes the transformers to run hotter due to saturation
of the iron laminations.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[[email protected]]

So what? The paper used to make the capacitors was high in acid
content. As the caps age, they start to adsorb moisture which breaks
down the fibers and the dielectric develops leakage.

That will change the bias voltage on the grids, which cause the tubes
to conduct harder. That puts a heavier load on an already overworked
power transformer. A ot of those old radios were built for a lower line
voltage, which causes the transformers to run hotter due to saturation
of the iron laminations.

I'm about the same age as Baron. I used to putter with electronics
and got my parts from old tvs and other stuff too.

I also tore apart capacitors and still recall having several
electrolytic caps explode. Particularly those VERY old oil filled
ones. So of course I'd have to investigate all the pieces.

My favorites were the Mica Capacitors. I'm still wondering how they
were made, and how were the wires attached? I just liked the look of
them with all the colored dots on them. Listed on site below as well
as pictures of them.
http://www.sayedsaad.com/fundmental/14_Fixed Capacitor.htm

In an article (below), they mention the Silver Mica caps (which came
out later). It says they were plated. How does one plate mica? And
how does one get the right thickness of mica, knowing how it's all
random pieces. But the article does not mention the make-up of the
original Mica Caps.

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

And what the heck is Tantalum?

This site is interesting and has some info on old caps.
http://www.vcomp.co.uk/index.htm

 

[bz]

My favorites were the Mica Capacitors. I'm still wondering how they
were made, and how were the wires attached? I just liked the look of
them with all the colored dots on them. Listed on site below as well
as pictures of them.
http://www.sayedsaad.com/fundmental/14_Fixed Capacitor.htm

In an article (below), they mention the Silver Mica caps (which came
out later). It says they were plated. How does one plate mica? And
how does one get the right thickness of mica, knowing how it's all
random pieces.

I made ceramic capacitors in the late 60's and early 70's for Sprague
Electric co. so I can make some guesses as to how the micas were made, or
tell you how I would do it.

Mica comes in large sheets that are rather uniform in thickness.
I would use a chemical reaction http://www.finishing.com/0400-
0599/415.shtml to plate the mica on both sides and measure the capacitance
of the large sheet.
From that value, I would know what sizes to cut the sheet into in order to
make many mica capacitors of 'about the desired value'.

I would then cut the sheet up into a bunch of small capacitors, solder on
leads, and then use injection molding to make the case.

Of course, each finished capacitor would be tested for value and the actual
value put on the case.

We did something rather similar when making ceramic capacitors. We had a
target value for the batch we were making, used silk screen printing to
print patterns of electrodes onto a layer of green[unfired] ceramic
laid down another layer of ceramic slip, printed more electrodes, continued
until we had enough 'area' to give the desired cap. We would then break up
the sheet into hundreds of 'green' capacitors, 'fire' them in a kiln,
abrade the edges to expose the electrodes, dip the ends in conductive ink
and bake it on, solder on leads and cover coat.
We would then test them for value and stamp them.

But the article does not mention the make-up of the
original Mica Caps.

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

And what the heck is Tantalum?

An element. A metal. Right under Niobium and Vanadium in the periodic
table, between Hafnium and Tungsten.
It can be used to produce a rather high value electrolytic capacitor as
aluminum is still used for some electrolytic.






--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

 

[[email protected]]

[email protected] wrote in

My favorites were the Mica Capacitors. I'm still wondering how they
were made, and how were the wires attached? I just liked the look of
them with all the colored dots on them. Listed on site below as well
as pictures of them.
http://www.sayedsaad.com/fundmental/14_Fixed Capacitor.htm

In an article (below), they mention the Silver Mica caps (which came
out later). It says they were plated. How does one plate mica? And
how does one get the right thickness of mica, knowing how it's all
random pieces.

I made ceramic capacitors in the late 60's and early 70's for Sprague
Electric co. so I can make some guesses as to how the micas were made, or
tell you how I would do it.

Mica comes in large sheets that are rather uniform in thickness.
I would use a chemical reaction http://www.finishing.com/0400-
0599/415.shtml to plate the mica on both sides and measure the capacitance
of the large sheet.
From that value, I would know what sizes to cut the sheet into in order to
make many mica capacitors of 'about the desired value'.

I would then cut the sheet up into a bunch of small capacitors, solder on
leads, and then use injection molding to make the case.

Of course, each finished capacitor would be tested for value and the actual
value put on the case.

We did something rather similar when making ceramic capacitors. We had a
target value for the batch we were making, used silk screen printing to
print patterns of electrodes onto a layer of green[unfired] ceramic
laid down another layer of ceramic slip, printed more electrodes, continued
until we had enough 'area' to give the desired cap. We would then break up
the sheet into hundreds of 'green' capacitors, 'fire' them in a kiln,
abrade the edges to expose the electrodes, dip the ends in conductive ink
and bake it on, solder on leads and cover coat.
We would then test them for value and stamp them.

But the article does not mention the make-up of the
original Mica Caps.

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.php

And what the heck is Tantalum?

An element. A metal. Right under Niobium and Vanadium in the periodic
table, between Hafnium and Tungsten.
It can be used to produce a rather high value electrolytic capacitor as
aluminum is still used for some electrolytic.

Thanks for the info. I always wondered how they made the caps. I
never thought they would be made in sheets, and thought each was made
separately. I did suspect that they would be tested to insure
reliability. I'm sure none of them would be 100% accurate if made in
sheets like that, plus the mica would be less likely to be accurate
compared to the man made ceramics. I would imagine most of the lead
soldering and cutting would all be done by machine, right?

I never learned much chemistry, I just looked up Tantalum on
wikipedia. I never heard of that as a metal.

Now I am thinking how they make resistors. I'll assume they are made
in long strands, sort of like spaghetti and cut up. But how they
attach the leads to a piece of carbon is another thing.

Thanks again, interesting information.

 

[bz]

[email protected] wrote in

My favorites were the Mica Capacitors. I'm still wondering how they
were made, and how were the wires attached? I just liked the look of
them with all the colored dots on them. Listed on site below as well
as pictures of them.
http://www.sayedsaad.com/fundmental/14_Fixed Capacitor.htm

In an article (below), they mention the Silver Mica caps (which came
out later). It says they were plated. How does one plate mica? And
how does one get the right thickness of mica, knowing how it's all
random pieces.

I made ceramic capacitors in the late 60's and early 70's for Sprague
Electric co. so I can make some guesses as to how the micas were made,
or tell you how I would do it.

Mica comes in large sheets that are rather uniform in thickness.
I would use a chemical reaction http://www.finishing.com/0400-
0599/415.shtml to plate the mica on both sides and measure the
capacitance of the large sheet.
From that value, I would know what sizes to cut the sheet into in order
to make many mica capacitors of 'about the desired value'.

I would then cut the sheet up into a bunch of small capacitors, solder
on leads, and then use injection molding to make the case.

Of course, each finished capacitor would be tested for value and the
actual value put on the case.

We did something rather similar when making ceramic capacitors. We had a
target value for the batch we were making, used silk screen printing to
print patterns of electrodes onto a layer of green[unfired] ceramic
laid down another layer of ceramic slip, printed more electrodes,
continued until we had enough 'area' to give the desired cap. We would
then break up the sheet into hundreds of 'green' capacitors, 'fire' them
in a kiln, abrade the edges to expose the electrodes, dip the ends in
conductive ink and bake it on, solder on leads and cover coat.
We would then test them for value and stamp them.

But the article does not mention the make-up of the
original Mica Caps.

http://www.radio-electronics.com/info/data/capacitor/capacitor_types.ph
p

And what the heck is Tantalum?

An element. A metal. Right under Niobium and Vanadium in the periodic
table, between Hafnium and Tungsten.
It can be used to produce a rather high value electrolytic capacitor as
aluminum is still used for some electrolytic.

Thanks for the info. I always wondered how they made the caps. I
never thought they would be made in sheets, and thought each was made
separately. I did suspect that they would be tested to insure
reliability. I'm sure none of them would be 100% accurate if made in
sheets like that, plus the mica would be less likely to be accurate
compared to the man made ceramics. I would imagine most of the lead
soldering and cutting would all be done by machine, right?

The leads were cut to length and taped to a cardboard carrier.
There might be 20 or so pairs of leads per carrier strip.
The carrier was placed in a jig and the chips were hand loaded.
A spring held the leads against the chip and the friction between chip and
leads kept the chip in place while the jig was lowered through a layer of
hot oil into the molten solder.

For some parts, the chips and leads were in a jig that carried them over a
fountain of molten solder (wave soldering machine).

I never learned much chemistry, I just looked up Tantalum on
wikipedia. I never heard of that as a metal.

Now I am thinking how they make resistors. I'll assume they are made
in long strands, sort of like spaghetti and cut up. But how they
attach the leads to a piece of carbon is another thing.

We made our resistors by silk screen printing an organo-metallic ink onto a
ceramic substrate.
They were then passed through a kiln, where the organic materials burned
away, leaving a thin-film resistor.

Now-days, vacuum deposition is used to make most metal film resistors.

I don't know how carbon resistors are made, sorry.

An interesting feature of a resistive film is that it has a certain
resistance in 'ohms per square'.

It doesn't matter WHAT size the square is. [power rating DOES depend on
size, but not resistance].

If you want higher resistance, you make the resistor LONGER. If you want
lower, you make it WIDER.

Thanks again, interesting information.

Learning is fun. Have fun!



--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap