[Heathkit] DX-40 Keying trouble

[Carl]

None of their other value black caps had that problem, we were told it was a 
processing mistake on the production line, no material engineering involved.

Id suspect your "expert" was looking to impress you. Now what transpires 
after 45 years is something else again.

Carl



----- Original Message ----- 
From: "Robert Nickels" <ranickel at comcast.net>
To: "Carl" <km1h at jeremy.mv.com>
Cc: <W9RAN at oneradio.net>; <heathkit at mailman.qth.net>
Sent: Monday, August 30, 2010 9:06 PM
Subject: Re: [Heathkit] DX-40 Keying trouble


>  On 8/30/2010 6:52 PM, Carl wrote:
>>
>> CDE admitted they tried a new process and I seriously doubt if any silver 
>> was involved.
>
> I'm not a materials engineer, but the fellow who looked at one of the 
> failed CDE disc ceramics from my 75-series HRO-500 was, and he recognized 
> the problem immediately, as it's very common in thick-film circuits that 
> use similar lead-attach metallurgy.  The tendency of silver to creep on 
> ceramic surfaces or into grain boundaries in the presence of an electric 
> field means that an alloy of silver-palladium or silver-palladium-gold is 
> generally used.    Contact with moisture or molten solder accelerate the 
> failure mechanism.
>
> 73, Bob W9RAN