I third the motion. You can actually calculate the needed capacity in any
particular circuit, whether it be bypassing or coupling. The chance that
any particular .05ufd capacitor originally used by the reeceiver
manufacturer would be the calculated value is about as as slim as finding a
nice SX-88 at a landfill. Ballpark is close enough, unless it is in a tuned
circuit.

And, the capacitors usually have a tolerance far greater than the .03 ufd
difference.

Use the .047 and do not give it another thought.

73, Colin K7FM

COLIN LAMB wrote:
I third the motion. You can actually calculate the needed capacity in any
particular circuit, whether it be bypassing or coupling. The chance that
any particular .05ufd capacitor originally used by the reeceiver
manufacturer would be the calculated value is about as as slim as finding a
nice SX-88 at a landfill. Ballpark is close enough, unless it is in a tuned
circuit.

Note that some of these WILL be in tuned circuits, and you'll almost certainly
need to realign the receiver with a sweep generator afterward. But that is
not a bad thing.

And, the capacitors usually have a tolerance far greater than the .03 ufd
difference.

Yes, figure 20% tolerances on those things.

Use the .047 and do not give it another thought.

If you really worry, you can get .05 uF orange drops.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

about as as slim as finding a nice SX-88 at a landfill.

Hey, whaddya mean?!?

http://www.antiqueradio.org/dumpster.htm

:-)

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/html

P.S. I agree with other responders that the .047 is a fine replacement.
Since the old caps were manufactured to such a wide tolerance, your modern
replacements may be closer to the specified value than most of the
originals!

And, Phil's website is as good and concise as it gets about replacing
capacitors. See http://antiqueradio.org/recap.htm

Even if you have been doing it for years, you will appreciate Phil's nice
writing style and useful information.

And, a big fat A for taking the time to help spread his wisdom, learned from
years of experience.

Even after years of repairing radios, we learn that we can do it better. A
few years ago I was going to replace a paper cap in a 17 tube receiver. I
do them one at a time. I clipped the old one out, got a phone call and
dinner call and shut the soldering iron off and left. I was not able to
return to the work for about a month. By then, I knew there was a capacitor
out - but I had clipped the old leads off and it took me an hour of tracing
and schematic reading before I could determine where the missing capacitor
was. Now, I am more methodical and make notes before I clip the capacitor.
A notebook and pencil are always nearby to document before I start work.
Life has been much simpler since then. And, it really is a good idea to
test the radio after a maximum number of changes.

Colin K7FM

"COLIN LAMB" wrote in message
...
And, Phil's website is as good and concise as it gets about replacing
capacitors. See http://antiqueradio.org/recap.htm
was. Now, I am more methodical and make notes before I clip the
capacitor. A notebook and pencil are always nearby to document before I
start work. Life has been much simpler since then. And, it really is a
good idea to test the radio after a maximum number of changes.

Colin K7FM


Keep a cheap set of imported clip leads handy. Place a set over the snipped
leads to "remind" where the old part was snipped from.

Digital photos of sections of the under chassis are also great visual
reminders.

Pete k1zjh

"Keep a cheap set of imported clip leads handy. Place a set over the snipped
leads to "remind" where the old part was snipped from."

Great Idea. Why didn't I think of that. Now I will be able to keep
repairing radios clear into senility.

Thanks, Colin K7FM

On Oct 17, 7:38 pm, "COLIN LAMB" wrote:
And, Phil's website is as good and concise as it gets about replacing
capacitors. Seehttp://antiqueradio.org/recap.htm

Even if you have been doing it for years, you will appreciate Phil's nice
writing style and useful information.

And, a big fat A for taking the time to help spread his wisdom, learned from
years of experience.

Even after years of repairing radios, we learn that we can do it better. A
few years ago I was going to replace a paper cap in a 17 tube receiver. I
do them one at a time. I clipped the old one out, got a phone call and
dinner call and shut the soldering iron off and left. I was not able to
return to the work for about a month. By then, I knew there was a capacitor
out - but I had clipped the old leads off and it took me an hour of tracing
and schematic reading before I could determine where the missing capacitor
was. Now, I am more methodical and make notes before I clip the capacitor.
A notebook and pencil are always nearby to document before I start work.
Life has been much simpler since then. And, it really is a good idea to
test the radio after a maximum number of changes.

Colin K7FM

Colin has it right. I had a similar experience. Ever since, I keep a
digital camera close and take close-up pictures as the work
progresses. I can always check my work, and I have a set of pictures
afterwards to show off.
I also keep a scratch copy of the radio manual's component list and
schematic that I mark up during the job. When I hand the radio over to
the owner, I can show him exactly what I did to restore the radio.
Gary WA7MLK

"COLIN LAMB" wrote in message
...
And, Phil's website is as good and concise as it gets
about replacing capacitors. See
http://antiqueradio.org/recap.htm

Even if you have been doing it for years, you will
appreciate Phil's nice writing style and useful
information.

And, a big fat A for taking the time to help spread his
wisdom, learned from years of experience.

Even after years of repairing radios, we learn that we can
do it better. A few years ago I was going to replace a
paper cap in a 17 tube receiver. I do them one at a time.
I clipped the old one out, got a phone call and dinner
call and shut the soldering iron off and left. I was not
able to return to the work for about a month. By then, I
knew there was a capacitor out - but I had clipped the old
leads off and it took me an hour of tracing and schematic
reading before I could determine where the missing
capacitor was. Now, I am more methodical and make notes
before I clip the capacitor. A notebook and pencil are
always nearby to document before I start work. Life has
been much simpler since then. And, it really is a good
idea to test the radio after a maximum number of changes.

Colin K7FM
I will add to what is on this page that the flat molded
caps are often also mica types, however, they are not
silvered micas. They are simply stacks of alternating mica
dielectric and foil plates. They are not as reliable or high
performance as silvered micas and should be checked. These
were used mostly in high voltage applications or where waxed
paper had too much loss.
Black Beauty caps are not exactly paper dielectric but
used paper impregnated with a polyester. They _should_ have
been low loss and quite reliable but became notorious within
a few years of their manufacture for developing high losses.
I suspect this may have been due to some problem with the
molded casing because Sprague sold capacotors with a similar
construction but in dipped epoxy casing as Orange Drops and
I have not heard that they shared the same short life
problems.
BTW, while silvered mica caps are generally very
reliable they can still go bad. I've had to replace quite a
few in rebuilding a couple of SP-600-JX's due to
instability. Here again all were molded bakelite cases so I
suspect either the case or perhaps end connections. Again,
the dipped epoxy mica caps do not seem to suffer from this
problem.


--
---
Richard Knoppow
Los Angeles, CA, USA

Yes, the flat molded micas are starting to show their age. Although
generally more reliable than paper, I have found some bad ones in recent
1940s TV projects.

When in doubt, check 'em!

I read somewhere else that the plastic casing in Black Beauties, etc.,
developed microscopic cracks and admitted water vapor over the years,
causing the same problems as in paper caps.

Phil Nelson

"Phil Nelson" wrote in message
...
Yes, the flat molded micas are starting to show their age.
Although generally more reliable than paper, I have found
some bad ones in recent 1940s TV projects.

When in doubt, check 'em!

I read somewhere else that the plastic casing in Black
Beauties, etc., developed microscopic cracks and admitted
water vapor over the years, causing the same problems as
in paper caps.

Phil Nelson
That may be, they certainly develop very large cracks
sometimes. I've disected a few BBs. The capacitor itself was
distorted, oddly flattened rather than being tubular.
Perhaps they were wound this way or perhaps some sort of
differential shrinkage of the encapsulation pushed them out
of shape. They were _supposed_ to be very long life, low
leakage, deluxe capacitors and are generally found in high
quality equipment.


--
---
Richard Knoppow
Los Angeles, CA, USA