[Hallicrafters] Need temprature compensating capacitors!

[Roy Morgan]

At 07:50 PM 8/31/2005, Jim Liles wrote:
>...temperature compensating tubular ceramic ... Any ideas as to a source?

Jim,

The Robber Barons of Nebraska have them:
http://www.surplussales.com/Capacitors/RF-TempDogbone.html
(Prices vary from 90 cents to $5.00 each.  Lest you be tempted to buy from 
them, they do not list any of the values you mention.)

Try:
<http://www.avxcorp.com/>http://www.avxcorp.com/
At this site I find their specs for a range of caps:
http://www.avxcorp.com/docs/Catalogs/clsi-tc.pdf


http://www.presidiocomponent.com
Here, I found this:
http://www.presidiocomponents.com/images/lit/TempCompCaps.pdf
and the proud claim that their caps are on the mars rovers.


<http://www.johanson-caps.com/>http://www.johanson-caps.com/
These guys have fancy rf caps but do not list any tempco types


"The President's Page" at Max Gain Systems used to have tempco caps - send 
them an email (I had good service buying a transformer or two from them...)
http://www.mgs4u.com/president_contents.htm

Temperature compensating an oscillator is tricky business, and success 
comes from both art and engineering patiently applied.  One little bit you 
may run into is this:

If you have more than one tempco cap in parallel, the overall coefficient 
is a weighted average of all caps.  For example, if you have a 30 pf N500 
and a 60 pf N750 in parallel, the over all cap will be about 90 pf but the 
temp coefficient will be:
(30/90)x500 + (60/90)x750
This leads you to realize that you can arrive at a different assembly of 
caps than you original had and still have good compensation.

A second trick I have seen is the use of two tempco caps and a differential 
variable cap to allow continuous adjustment of compensation. The variable's 
rotor goes to ground, and from each of the two stators, equal caps of very 
different compensation factors go to the tuned circuit.  By changing the 
variable, you get differing amounts of each compensating cap applied to the 
circuit but overall not much change in total capacitance.  I can't remember 
what equipment this was used in, but it was likely military due to the cost 
involved.

Do let us all know where you found the caps you need.  Some of us have 
R-390 and S-line PTO's that may one day get a really thorough rebuild, 
including re-compensation.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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