Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Tam/WB2TT

Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Tam/WB2TT

Perhaps you were talking about bypass type ceramics, but the posting I
responded to:


Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

made no such qualification, and even specifically mentioned "black
tipped" (usually NPO) capacitors.

As far as I know, silver micas are getting pretty rare, except maybe for
very high power, high current RF applications, if they're being used for
even that any more. I doubt if they exist as surface mount parts. The
reason silver micas are hard to find and expensive is that they've been
made obsolete for nearly all applications by generally superior ceramic
types.

Roy Lewallen, W7EL

Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Tam/WB2TT

Perhaps you were talking about bypass type ceramics, but the posting I
responded to:


Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

made no such qualification, and even specifically mentioned "black
tipped" (usually NPO) capacitors.

As far as I know, silver micas are getting pretty rare, except maybe for
very high power, high current RF applications, if they're being used for
even that any more. I doubt if they exist as surface mount parts. The
reason silver micas are hard to find and expensive is that they've been
made obsolete for nearly all applications by generally superior ceramic
types.

Roy Lewallen, W7EL

In article ,
Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Cornell Dubilier / Waldom makes surace mount siler mico caps. You can
get them from Digikey for under $10 US.

You can get standard PPS film capacitors from several makers. If you
don't mind the fact that they are very touchy and have a higher failure
rate they may be an option. If you want a little better, you can buy the
more costly coated ones.

I wouldn't say that you are forced into using ceramic. It is an option
you may perfer.

--
--
forging knowledge

In article ,
Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Cornell Dubilier / Waldom makes surace mount siler mico caps. You can
get them from Digikey for under $10 US.

You can get standard PPS film capacitors from several makers. If you
don't mind the fact that they are very touchy and have a higher failure
rate they may be an option. If you want a little better, you can buy the
more costly coated ones.

I wouldn't say that you are forced into using ceramic. It is an option
you may perfer.

--
--
forging knowledge

On Tue, 23 Mar 2004 14:44:30 +0000 (UTC),
(Ken Smith) wrote:

In article ,
Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Cornell Dubilier / Waldom makes surace mount siler mico caps. You can
get them from Digikey for under $10 US.

The CDE "MC" series of cazapitors are "mica", not "silver mica". The
difference is that silver mica caps have to be sealed (dipped) or the
silver plating reacts with everything. I'm not sure what plating is
used for the "MC" series of surface mount mica. My guess(tm) is
aluminum.
http://www.cornell-dubilier.com/mica/mica.htm
http://www.cornell-dubilier.com/film/hmc.htm
http://www.cornell-dubilier.com/catalogs/MC.pdf

The big advantages of silver mica is stability, wide temp range, very
low dissipation, and tolerance to over voltage spikes. Many years
ago, I wasted a month working over an HF xmitter, trying to design out
the expensive silver mica and porcelain cazapitors and replace them
with cheaper ceramics. It was possible for the low power drivers but
a waste of time in areas that had high RF currents or required good
stability. A similar cost reduction exercise was also being done on
the automagic antenna tuner (by someone else) with similar results.
The project ended when someone suggested using high temp silver solder
to prevent the ceramic caps from reflowing their solder connections
and falling off the board.

I guess(tm) the reason that silver mica caps are difficult to find is
that there are few companies producing high power RF products as
compared to the huge number of low power RF products. It's not a big
market that probably can only support a few specialty component
vendors.


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS

On Tue, 23 Mar 2004 14:44:30 +0000 (UTC),
(Ken Smith) wrote:

In article ,
Tam/WB2TT wrote:
Roy,

We were talking about bypass type ceramics. See the 3/20 10:13AM posting.
BTW, I think with SM you are pretty much forced into using ceramics.

Cornell Dubilier / Waldom makes surace mount siler mico caps. You can
get them from Digikey for under $10 US.

The CDE "MC" series of cazapitors are "mica", not "silver mica". The
difference is that silver mica caps have to be sealed (dipped) or the
silver plating reacts with everything. I'm not sure what plating is
used for the "MC" series of surface mount mica. My guess(tm) is
aluminum.
http://www.cornell-dubilier.com/mica/mica.htm
http://www.cornell-dubilier.com/film/hmc.htm
http://www.cornell-dubilier.com/catalogs/MC.pdf

The big advantages of silver mica is stability, wide temp range, very
low dissipation, and tolerance to over voltage spikes. Many years
ago, I wasted a month working over an HF xmitter, trying to design out
the expensive silver mica and porcelain cazapitors and replace them
with cheaper ceramics. It was possible for the low power drivers but
a waste of time in areas that had high RF currents or required good
stability. A similar cost reduction exercise was also being done on
the automagic antenna tuner (by someone else) with similar results.
The project ended when someone suggested using high temp silver solder
to prevent the ceramic caps from reflowing their solder connections
and falling off the board.

I guess(tm) the reason that silver mica caps are difficult to find is
that there are few companies producing high power RF products as
compared to the huge number of low power RF products. It's not a big
market that probably can only support a few specialty component
vendors.


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS

Roy Lewallen wrote in message ...
Paul Burridge wrote:

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

I strongly disagree with this. I've successfully used ceramic capacitors
many times for both high and low Q tuned circuits from HF to UHF. Years
ago, I found that NPO ceramics were decidedly superior to silver micas
for temperature stability, so I use them exclusively for VFO tank circuits.

....

In agreement and support of what Roy wrote, I'd toss out some
additional notes:

o I've seen (been the vicitm of?) silvered micas that exhibit random
tiny jumps in capacitance, which is a really bad thing in oscillators.

o You can get X7R dielectric SMT caps in SMT up to at least 0.1uF in
0603 size, for low voltage ratings. See manufacturers' data sheets
for the largest currently available values. I suspect reliability
suffers if you try to use ones with too high a C*V/unit volume,
though.

o As someone recently pointed out to me (Sphero, I think it was), you
can get C0G up to 0.1uF in SMT--I think he said in 1206 size.

o It's possible to get 1% C0G caps.

o A C0G is probably about the cheapest electronic component you'll
find with a maximum 30ppm/C temperature coefficient (though beware,
some C0Gs I've seen are rated up to 60ppm/C).

o There are special high-Q ceramics that are better than standard
C0Gs for use at microwave frequencies...generally above 1GHz.

Cheers,
Tom

Roy Lewallen wrote in message ...
Paul Burridge wrote:

Yes, ceramics are *hopeless* for tuned circuits; I wouldn't trust the
black tipped ones, either. You can't beat silver mica but they're a
bit hard to find and expensive.

I strongly disagree with this. I've successfully used ceramic capacitors
many times for both high and low Q tuned circuits from HF to UHF. Years
ago, I found that NPO ceramics were decidedly superior to silver micas
for temperature stability, so I use them exclusively for VFO tank circuits.

....

In agreement and support of what Roy wrote, I'd toss out some
additional notes:

o I've seen (been the vicitm of?) silvered micas that exhibit random
tiny jumps in capacitance, which is a really bad thing in oscillators.

o You can get X7R dielectric SMT caps in SMT up to at least 0.1uF in
0603 size, for low voltage ratings. See manufacturers' data sheets
for the largest currently available values. I suspect reliability
suffers if you try to use ones with too high a C*V/unit volume,
though.

o As someone recently pointed out to me (Sphero, I think it was), you
can get C0G up to 0.1uF in SMT--I think he said in 1206 size.

o It's possible to get 1% C0G caps.

o A C0G is probably about the cheapest electronic component you'll
find with a maximum 30ppm/C temperature coefficient (though beware,
some C0Gs I've seen are rated up to 60ppm/C).

o There are special high-Q ceramics that are better than standard
C0Gs for use at microwave frequencies...generally above 1GHz.

Cheers,
Tom

"Tom Bruhns" a écrit dans le message news:
...

snip
o It's possible to get 1% C0G caps.


Tom,
do you know any supplier of such for proto quantity ?
I need 1n/0805 and 4.7n/1206.
I can't find any of these and I feel I'll have to buy a handfull of 5%, sort
them and maybe adapt the resitors values to what the lot would kindly give
me.
Not very entertaining.


o A C0G is probably about the cheapest electronic component you'll
find with a maximum 30ppm/C temperature coefficient (though beware,
some C0Gs I've seen are rated up to 60ppm/C).


Do you have any name ?


Thanks,
Fred.