Hello Everyone,
The topic of the day is using Multilayer Ceramic Capacitors Instead Mica Capacitors .
As you guys have known Mica Capacitors prices are getting more expensive and some values are getting harder to get .
More and More I am seeing that dreaded monster Silver migration Disease and the current value that I need to stock up on and use in a General Electric 1950s clock radio 110 PF.
I found these Multilayer Ceramic capacitors made by Kemet
It does say Class I "stable" material. Components of this classification are temperature compensating and are suited for resonant circuit applications or those where Q and stability of capacitance characteristics are required.
an NP0 (C0G) cap is a better cap when it comes to stability, so if you could find a cap that is an NP0 with the proper capacitance vs WV, use it. Micas are very good and stable, and due to more capacitance per volume unit and higher WV are preferred in some circuits.
The rest, well, could be use in some places and should not be used anywhere where the stability of Mica is important.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
I guess I'm going to have to mold my own from that hunk of South Dakota Mica I have up at the cabin. Let's see, a slice of mica, couple "plates" and some JB Weld should be just fine (maybe some colored markers to show the value). Come on kids, it's craft time!
Hello Rob,
Yes , I could do this as a classroom project go to mouser and look at some the prices for the larger Mica capacitors I just went to mouser and looked at a 7500pf at 500 volts around $22.00 that crazy right buy 10 of those .
For the purpose, I do not think anything beats NP0. They simply did not exist at the time, and the mica were the best (and they are great, considering they are as good today as they were the day they were made). But C0G has Zero ppm temp drift.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
SMD is silver migration disease, not silver mica disease. If you think mica capacitors have gotten expensive, look at the prices of some silver mica capacitors. I have plenty of experience with silver mica capacitors used in professional electronics, especially in broadcast transmitters.
Hello Dale,
Yes I meant migration ! it was a long week .
for sure when buying those silver mica capacitors you need a home loan to buy I do have some in my stock .
The IF cans used in Japanese radios used either molded mica or those ceramic capacitors that look like a hollow dog bone resistor. In West German sets they used the dog bone ceramic jobs, as well as polystyrene, in tuned circuits, I guess that mica was harder to come by for them?
Regards
Arran
I use caution when replacing defective mica caps in frequency determining circuits. Often, they have a tempco even if not marked so the tuned circuit stays stable as the coil drifts with temperature. The earlier the radio the more likely the component is "house marked"
Same applies to the "dogbone" ceramics these are often tempco any more than three dots are suspect but where it is in the circuit is often a clue.
One of my first re-capping experience (1965) was with a Hammarlund SP-110-x horrible drift and unable to calibrate the center of the bands both RF and oscillator circuits. The OEM open mica caps were of a special brass/steel clinched (liken to bi-metal) construction that remained stable. However, time and moisture ruined them. Finding suitable values and temco was cut and try, the schematic available did not give values, though I no longer remember the value they were N330.
IMHO I do not think drift in a 455khz (sic) IF is a problem, I have not noticed it, but drift in a receiver that uses a higher IF such as a dual conversion drift in the IF is suspect.
The "discovery" of what appears to be a sure thing replacement for a mica condenser should not be an excuse to shotgun.
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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