Topband: TX relays

[Carl]

During the years I was running 10-40M stacks I used 24VDC surplus DPDT 
relays at .50-1.00 each from All Electronics; 12 or 13A contacts if I 
remember and in clear plastic dust covers. These were mounted in surplus 
CATV line fixtures (splitter, power combiner, etc).

After up to 15 years of heavy use when I dismantled the arrays they looked 
still as new inside and never once acted up.

IMO there is way too much fussing about things that have no effect at HF to 
most users.

Note also that all Ameritron switches use open relays, even the overpriced 
ones.
The supposedly idiot proof RCS-12 would be attractive at certain contest 
stations with operators still with training wheels.

Tom still hasnt answered why there is only a $10 price difference between 
the RCS-4 and the -8V yet users of the -8V are getting raped for replacement 
relays.

Carl
KM1H



----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "Stan Stockton" <wa5rtg at gmail.com>; "Milt -- N5IA" 
<n5ia at zia-connection.com>
Cc: <topband at contesting.com>
Sent: Friday, October 10, 2014 8:29 AM
Subject: Re: Topband: TX relays


>> I have built four or five "stack matches" using these relays and have 
>> been quite pleased with them.
>>
>> http://www.mouser.com/ProductDetail/TE-Connectivity/T92S11D22-12/?qs=%2fha2pyFadujQKxyiQ9QJsU9gOmzykpctnwthD3xoZjoJPHbNrun4hw%3d%3d
>>
>> 73...Stan, K5GO
>
> If you look at the contact material, it is the wrong material type for our 
> applications. Those relays are hot switch relays for high current 
> applications with Silver Cadmium Oxide. From an engineering bulletin on 
> selecting relay contact materials:
>
> Silver Cadmium Oxide
>
> Silver cadmium oxide contacts have long been used for switching loads
>
> that produce a high energy arc. Silver cadmium oxide contacts are less
>
> electrically conductive than fine silver contacts, but have superior
>
> resistance to material transfer and material loss due to arcing. They do
>
> exhibit greater interface resistance between mated contacts, and also a
>
> slightly greater contact assembly heat rise. The minimum arc voltagerating
>
> of silver cadmium oxide is 10 volts and, like fine silver contacts, the 
> silver
>
> in this alloy will oxidize and sulfidate. Therefore, an arc is necessary 
> to
>
> keep these contacts clean.
>
>
> This doesn't mean they won't work and will go up in smoke. It does mean 
> they are subject to contact sulfidation which causes intermittent receive. 
> They have silver, a hard base material, and large contact area that does 
> not wipe well. They also are the type of relay that is subject to contact 
> derating from skin effect because of constant resistivity.
>
>
> 73 Tom
>
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