have an 'audio filter' package that sits between the output of 1rst
audio 6c5 and a tone control. shot; needs rebuilt. 1940 national.

am looking at mouser for suitable chokes. there are waaaay too many
choices... vintage electronics did not have any suitable....

what is best generic part for this application? ie i need to narrow
down 100's they offer to what i need in some way. was looking at
fastron epoxy mcc/n series. can't find the exact values, either. can
get w/in 20-30 MH. how critical?

schemo gives two 'filters' (choke/inductor) valued at 175MH and
360MH. also in the package are two mica caps .006mfd and .011mfd.

the values seem hard to find for micas -- is 'orange dip' substitution
for this ok? i can turn up these micas up on mouser but at $6-25 (!)
each, depending on specs.
thx much all help.
ab

The price of wheat is certainly going up. The largest mica value I have
is 5100pf. I don't see why an Orange Drops wouldn't work, though.
Nothing special about the circuit, for sure.

ablebravo wrote:
have an 'audio filter' package that sits between the output of 1rst
audio 6c5 and a tone control. shot; needs rebuilt. 1940 national.

am looking at mouser for suitable chokes. there are waaaay too many
choices... vintage electronics did not have any suitable....

what is best generic part for this application? ie i need to narrow
down 100's they offer to what i need in some way. was looking at
fastron epoxy mcc/n series. can't find the exact values, either. can
get w/in 20-30 MH. how critical?

schemo gives two 'filters' (choke/inductor) valued at 175MH and
360MH. also in the package are two mica caps .006mfd and .011mfd.

the values seem hard to find for micas -- is 'orange dip' substitution
for this ok? i can turn up these micas up on mouser but at $6-25 (!)
each, depending on specs.
thx much all help.
ab

ablebravo wrote:

what is best generic part for this application? ie i need to narrow
down 100's they offer to what i need in some way. was looking at
fastron epoxy mcc/n series. can't find the exact values, either. can
get w/in 20-30 MH. how critical?

Not very, though it will change the filter frequencies by a little bit.
They aren't super sharp, though.

How did the inductors fail, though? They hardly ever do, unless a cap
fails and throws DC on them.

schemo gives two 'filters' (choke/inductor) valued at 175MH and
360MH. also in the package are two mica caps .006mfd and .011mfd.

Miller makes some inductors in that range that Digi-Key stocks. If you
want to be right on, get larger ones than you need and take off winds
until the value is correct. Higher current inductors are easy to do this
with.

the values seem hard to find for micas -- is 'orange dip' substitution
for this ok? i can turn up these micas up on mouser but at $6-25 (!)
each, depending on specs.

Yes, but again, mica caps don't fail easily.

What makes you think these are bad?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

whole package broke loose and bounced around in shipping -- leads
damaged, mounting ear broken off. this was a surface mount package
screwed to the chassis top. caps when tested, way off value. thought
best to rebuild whole thing. did not know micas in these values so
expensive, as had only purchased low pf's before. also didn't know i
would be getting into 'choke lore'. live and learn.

ab

"ablebravo" ) writes:
whole package broke loose and bounced around in shipping -- leads
damaged, mounting ear broken off. this was a surface mount package
screwed to the chassis top. caps when tested, way off value. thought
best to rebuild whole thing. did not know micas in these values so
expensive, as had only purchased low pf's before. also didn't know i
would be getting into 'choke lore'. live and learn.

ab

But in the old days, there wasn't much choice but mica capacitors for
precision capacitors.

Likely things have improved, though I don't know if the other choices
are less expensive. Things like polystyrene capacitors have come
along in recent decades, and that sort of thing may be the place
to look.

What you don't want is a capacitor that has really large variation
between capacitors of the same nominal value, or likely capacitors
that change a lot with temperature.

Michael VE2BVW

"ablebravo" wrote in message
ups.com...
have an 'audio filter' package that sits between the
output of 1rst
audio 6c5 and a tone control. shot; needs rebuilt. 1940
national.

am looking at mouser for suitable chokes. there are
waaaay too many
choices... vintage electronics did not have any
suitable....

what is best generic part for this application? ie i need
to narrow
down 100's they offer to what i need in some way. was
looking at
fastron epoxy mcc/n series. can't find the exact values,
either. can
get w/in 20-30 MH. how critical?

schemo gives two 'filters' (choke/inductor) valued at
175MH and
360MH. also in the package are two mica caps .006mfd and
.011mfd.

the values seem hard to find for micas -- is 'orange dip'
substitution
for this ok? i can turn up these micas up on mouser but
at $6-25 (!)
each, depending on specs.
thx much all help.
ab

Are the caps specified as mica in the parts list?
There were actually two kinds of mica caps, one was the
familiar silvered mica where the "plates" of the capacitor
are plated onto the mica dielectric and the "stacked" mica
using foil. The former are the familiar very stable type the
latter were not so stable but could be made for relatively
high voltages. I suspect these are of the latter variety and
modern metalized plastic caps are better and more reliable.
BTW, despite reputation for high reliability of
silvered mica caps the older molded body type seem to fail
at fairly high rates. I just went through restoring an
SP-600-JX 17 which was in very good condition but have had
to replace at least half a dozen or more silver mica caps
because of instability. This is not to say they were bad,
after all, they are more than fifty years old.
You may be able to salvage the inductors depending on
what has happened to them. If the leads broke of the
terminals you may be able to simply resolder them. Its
certainly worth a try.


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




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