[Collins] 32S-3 caps C72, C76

[Carl]

I dont know of any 1000pf NPO 3 or 6KV disc.

In any case the 1000pf 6KV have been used as a blocking cap in amps 4-5 
times the output of a pair of 6146's with no history of failing.

The Heathkit SB-1000 uses a pair in parallel at 1000W out.

They are $ .72 at Mouser.

Carl
KM1H


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: "Bob and Sue Jefferis" <ljranch2010-gem at yahoo.com>
Cc: "Carl" <km1h at jeremy.mv.com>; <collins at mailman.qth.net>
Sent: Friday, May 04, 2012 3:26 PM
Subject: Re: [Collins] 32S-3 caps C72, C76


> 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
>>>>
>>>>
>>>> -
>
>
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