[Collins] 32S-3 caps C72, C76

[Dr. Gerald N. Johnson]

The "Hi-K" appears to have been used by several makers in the 1960 
Master, mostly for coupling and bypass capacitors where change in value 
is considered to be not much of a problem. But they didn't show any 
properties like capacitance vs temperature. And today places like:
http://www.luckytop.com.hk/pdf/LT-C-CAP-HI-K.pdf show a wide range of 
curves all for Hi-K ceramics.

If I had a need to replace these (or find a new one to update the 
neutralization circuit) I'd look for the biggest physical size that 
would fit the space so to get the lowest dielectric constant and the 
best temperature stability and the best current carrying capability. 
With maybe 500 volts RMS and with the tube and the neutralization C, the 
capacitor may have to carry a significant fraction of an amp, and a 
small cap (going anything smaller than what's there would be a bad idea) 
will heat more and so drift more. But they are also in the vicinity of 
the tubes so get plenty radiated heat. Going higher in voltage like the 
6 KV that Carl recommended gets more heat dissipating capability too. 
And while looking for the biggest that would fit I'd wish for a COG for 
lowest temperature coefficient. And that usually means the largest 
physical size for a given capacitance and voltage.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 5/4/2012 11:51 AM, Bob and Sue Jefferis wrote:
> Jerry,
>
> Thanks for the effort. The Collins part number and vendor number are consistent across all the 32S-3 and KWM-2 manuals I have, as you state. However, these are typical tan colored radial lead ceramic discs, not door knob transmitting caps with threaded posts.
>
> 73, Bob
> On May 4, 2012, at 7:25 AM, Dr. Gerald N. Johnson wrote:
>
>> My most rtecent manual shows those capacitors are part number
>> 858W5T2KV1KPFPORM20PCT 1nf, 2 kv, 20% CPN 913-4803-000 made by v72982,
>> looks like Centralab. A transmitting capacitor 13/16" diameter 5/8"
>> long, with 6-32 threaded posts. Hi-K dielectric according to the 1960
>> Radio Electronic Master. Centralab catalog 101 shows X5U maximum C at
>> room temp, down 20% at -25C and +50C. Probably like (CFC) HT581000-75 at
>> Surplus Sales or RF Parts. A disk ceramic may function electrically but
>> loses the mechanical support of the Centralab 858 capacitor.
>>
>> HP says federal manufacturing code 72982 is Erie. And my 1960 Master
>> doesn't show any erie transmitting capacitors.
>>
>> 73, Jerry, K0CQ, Technical adviser to the Collins Radio Association
>>
>> On 5/4/2012 8:01 AM, Carl wrote:
>>> Generic Hi-K of the 50's which was long before todays definitions were
>>> developed.
>>>
>>> Any 1000pf/6KV disc will be fine.
>>>
>>> Carl
>>> KM1H
>>>
>>>
>>> -