[Elecraft] K3 Intermittently loses gain

[Bill VanAlstyne W5WVO]

This failure modality, I believe, applies equally to all sorts of RF 
"connectors", which includes relay contacts as well as cable-end connectors. 
I've experienced similar failures twice over the past seven years.

In the most recent case -- and the symptoms were exactly as described in 
this thread -- it was the normally-closed (receive) contacts in the frame 
T-R relay in the amplifier. I fiddled with that relay for several weeks 
trying to get enough contact tension and/or wiping action on the "normally 
closed" side, and finally gave up and pitched it in the trash. I designed 
and built a completely new T-R system using name-brand high-speed vacuum 
relays and have never looked back. It works flawlessly, and at QSK speeds.

One final word -- "Made in China" does not necessarily mean cheap and 
shoddy, though it sometimes does. "Made in USA" does not necessarily mean 
high-quality, robust construction, though it sometimes does. It just isn't 
that simple any more. I have a pair of 3-500ZG triodes, for example, that 
came from RF Parts and were undoubtedly made in China. They are workhorse 
performers and have withstood years of abuse as well as a high-voltage 
glitch that fried a number of other components in the amplifier. On the 
other hand, I am with those who use spend the extra money for Amphenol RF 
connector parts, not because they are always made in the USA (they aren't, 
apparently), but because I trust the COMPANY to produce quality parts in 
whatever country they choose to manufacture in.

Bill W5WVO



-----Original Message----- 
From: hb9ari
Sent: Tuesday, November 02, 2010 06:25
To: Elecraft-forum
Subject: Re: [Elecraft] K3 Intermittently loses gain

Hi  Ron,

Hi had a similar problem some months ago.
Symptoms:

Suddenly loss of sensitivity ~ -20 to -40dB or more...
Transmission was always ok.
Measurement with miniVNA always correct (at ~0dBm power).
Moving some connections remove sometimes the loss of sensitivity.
(but all soldered or crimped connections were tested as 100% ok,
no "cold" solder joint, or broken wire, etc)

After searching a lot of time, i suspected "old" silvered connectors,
plugs, etc
Changing all  connectors with non silvered ones, all is now perfect!
My explanation, accepted by other OM, is the following:
My "old" idea, (ham since 1970) was that silver oxide was conducting,
may be true, but over an (undefined for the moment...) level.
In RX mode, in the uV range, i suppose that the potential is
insufficient to break the  ultra thin sliver oxide layer.
With 0dBm or more "level", the oxide layer should be broken and
all is ok. If  i'm correct , some mechanicals relays are not specified
under some voltage levels and to commutate very low voltages,
some "special" kind of metal contacts must be used.
Since this "incident" ALL silvered plated connectors, plug, etc
are banned from the shack ! I never had problem since
i've taken this decision.

My best 73,

Rudi, HB9ARI

Ron W3ZV wrote:
> Started to play in the CQWWSSB. K3 started to exhibit intermittent loss
> of gain after a transmission. Sometimes, stomping on the foot switch
> brings it back up. Sometimes it takes a short transmission.  No real
> pattern to when it occurs. Receiver isn't totally deaf. Just way down.
> Any ideas as to where the problem might be? I'm guessing its time for
> the radio to take a trip home to the left coast.
>
> Ron W3ZV
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