Micamold capacitor

[Lee K. Gleason]

Hello all. I'm restoring an old radio, and in the process of replacing
the assorted electrolytic caps, I came across a half melted looking wax
coated cylindrical cap. The only markings on it are "Micamold 420E2503. On
the next line, it says ".05 plus or minus 20 150". It's a tubular shape, not
the usual postage stamp or lozenge shape that Micamold caps usually are.
It's got a band on one end, so I'm guessing it's polarized - although the
end without the band is grounded, the opposite of what I would have guessed.
I'm guessing, .05MFD, 150 volts. I can't just look it up in the schematic,
since this this part of the radio is a circuit a previous owner added on to
support a Magic Eye tuning indicator tube. What do you think?

--
Lee K. Gleason N5ZMR
Control-G Consultants
lee.gleason@comcast.net

 

[Michael Black]

On Sun, 20 Nov 2011, Lee K. Gleason wrote:

Hello all. I'm restoring an old radio, and in the process of replacing
the assorted electrolytic caps, I came across a half melted looking wax
coated cylindrical cap. The only markings on it are "Micamold 420E2503. On
the next line, it says ".05 plus or minus 20 150". It's a tubular shape, not
the usual postage stamp or lozenge shape that Micamold caps usually are.
It's got a band on one end, so I'm guessing it's polarized - although the
end without the band is grounded, the opposite of what I would have guessed.
I'm guessing, .05MFD, 150 volts. I can't just look it up in the schematic,
since this this part of the radio is a circuit a previous owner added on to
support a Magic Eye tuning indicator tube. What do you think?

Why would it be polarized? People too often think there is some special

reason for polarized capacitors, when in reality I can think of no
application that would require a polarized capacitor. But, in order to
fit larger capacitance into reasonable size, capacitors become polarized
because they are made in a way that does cause them to be polarized.

One just looks at the value, and there's no way .05uF is large enough to
require an electrolytic or tantalum capacitor. Thus it can't be
polarized, there's no use in using them at that small capacitance.

What was common in the old days were capacitors where one side was best
put to ground. Paper capacitors for instance, since it's a roll of foil
interweaved with an insulator, one side will be more prone to stray
pickup, so it should be grounded, and capacitors were marked to indicate
which side. They will work in either direction, just that in one way it
may pick up unwanted signals.

But that won't be relevant today, since capacitors of .05uF can easily be
much smaller and with other materials, and there won't be a difference
which way it gets put in.

Michael

 

[flipper]

On Sun, 20 Nov 2011 22:07:02 -0600, "Lee K. Gleason"
<lee.gleason@comcast.net> wrote:

Hello all. I'm restoring an old radio, and in the process of replacing
the assorted electrolytic caps, I came across a half melted looking wax
coated cylindrical cap. The only markings on it are "Micamold 420E2503. On
the next line, it says ".05 plus or minus 20 150". It's a tubular shape, not
the usual postage stamp or lozenge shape that Micamold caps usually are.
It's got a band on one end, so I'm guessing it's polarized - although the
end without the band is grounded, the opposite of what I would have guessed.
I'm guessing, .05MFD, 150 volts. I can't just look it up in the schematic,
since this this part of the radio is a circuit a previous owner added on to
support a Magic Eye tuning indicator tube. What do you think?

From your description it sounds like a wax paper capacitor. The band
is not for electrical polarity but denotes which end is connected to
the outer foil, which was often connected to ground, assuming the
circuit allows, since that would then act like a 'shield'.

You should replace all the wax paper caps too, not just electrolytics,
because they fall apart, as you have noticed with that one.

Btw, you can't trust that the 'brick rectangle' ones are always mica
either. Micamold was notorious for making paper caps in that shape
(say, around 500pF or so and up) but others did it too.

..05uF, 150V sounds right.

 

[Lostgallifreyan]

"Lee K. Gleason" <lee.gleason@comcast.net> wrote in
news:4ec9ce92$0$18905$882e7ee2@usenet-news.net:

I'm guessing, .05MFD, 150 volts.

I agree. (And at 20% tolerance). And the 503 at the end of the other number
might be a forerunner of the notation now used, to mean 50,000pf so 0.05ľF.

 

[Hank]

In article <4ec9ce92$0$18905$882e7ee2@usenet-news.net>,
Lee K. Gleason <lee.gleason@comcast.net> wrote:

Hello all. I'm restoring an old radio, and in the process of replacing
the assorted electrolytic caps, I came across a half melted looking wax
coated cylindrical cap. The only markings on it are "Micamold 420E2503. On
the next line, it says ".05 plus or minus 20 150". It's a tubular shape, not
the usual postage stamp or lozenge shape that Micamold caps usually are.
It's got a band on one end, so I'm guessing it's polarized - although the
end without the band is grounded, the opposite of what I would have guessed.
I'm guessing, .05MFD, 150 volts. I can't just look it up in the schematic,
since this this part of the radio is a circuit a previous owner added on to
support a Magic Eye tuning indicator tube. What do you think?

Sounds like an ordinary old wax paper condenser, definitely not

polarized. What's its function in the circuit? Sounds like a real
home-brew mod, as if it is grounded, the band (outside foil) should
have gone to ground. An ordinary .05 mike mylar cap, 150 volts or higher,
is a replacement, if that value is suitable for the circuit function.

Hank

 

[Lee K. Gleason]

An ordinary .05 mike mylar cap, 150 volts or higher,

is a replacement, if that value is suitable for the circuit function.

Hank

Thanks all, for the info. I did that, and it works a treat!.
--
Lee K. Gleason N5ZMR
Control-G Consultants
lee.gleason@comcast.net