[Boatanchors] Temp comp caps

[james.liles at comcast.net]

ADDITIONAL INFORMATION:

I should have mention the most extensive inventory of Temperature compensating capacitors can be found at Surplus sales of Nebraska.  They have both Dog bone and Ceramic disc, class 1 TC caps at very reasonable prices.  

A second source is ebay.  Search on “Ceramic capacitors N” or “ceramic plate capacitors” using international extensions.

Early Ceramic Temp comp caps were Dog bone shaped.  They were replaced by Ceramic disc caps and later by Ceramic plate caps.

The early dog bone caps were the only group that had published data defining the rate of change with temp attributes.  Data was used for precision design. 

The Ceramic plate caps were available in 100v and 500v ratings.  I don’t believe you will find the 500v ceramic TC plate caps anywhere except the scalpers.  They will ask extraordinary prices along with a one time finders fee, write a mortgage on your home, and indenture your children and favorite pet.

Regardless of the version you purchase, the TC attributes should be measured.  The best NPO/COG and TC capacitors will have a published tolerance of +- 30ppm and the higher values will be 100’s of +- ppm .  There is no such thing as an NPO capacitor unless you get lucky.  Measure them before you use them.

Kindest regards Jim K9AXN          

--------------------  ORIGINAL NOTE ----------------------------------------

Good morning Paul:

They are not a thing of the past, simply not much demand.

I have a fairly extensive stock of TC caps that I use for VFO work.  What I have for your need is 4/2.2pf P100’s and a 1.2pf P100 to make the 10pf requirement.  They are 100v modern ceramic plate caps not dog bone.

Also on ebay you will find an 18pf P100 ceramic plate cap.  Search for
“Lot of 10 Low K Ceramic Plate Capacitor 18pF 100V 2222 638 04189”.

You get 10 for a dollar + shipping.  ebay is the best venue for these caps as you won’t find ceramic plate caps anywhere else --- except the scalpers where you will pay $30.00 apiece with a one time charge of $100.00 to $500.00.

Don’t know what your application is but might consider silver mica caps.  They are universally P30.  

You need 10pf at P100, but if you have more capacity to work with and can squeeze 23pf more plus the 10pf that you need for a total of 33pf, the silver mica caps will do the trick for you.

What are you working with Paul?

Kindest regards Jim K9AXN  


Message: 5
Date: Wed, 21 May 2014 10:31:18 -0500
From: "Paul Kraemer" <elespe at lisco.com>
To: <boatanchors at qth.net>
Subject: [Boatanchors] Temp comp caps
Message-ID: <014985AD3E4740AAB170C177152EBD07 at ENGR2>
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Looking for a couple 10 pfd ceramic capacitors with a positive temperature 
curve.  P100 to be exact.

Are these old temperature compensation caps a thing of the past.
I find some on internet but only negative types like N750 and such.

Any help appreciated

Paul K0UYA