[Elecraft] KPA500/KAT500 paired with AL-1500?

[Edward R Cole]

Just warning about the CX-600NL.  I initially used them for TR relays 
on 2m-eme at 100w to 600w with no problems but once I increased power 
to >800w the relays began to fail.  The contacts apparently not able 
to carry higher RF current as they eventually heat and melt the 
center wiper usually such that it shorts the coaxial section -- Not a 
nice thing to do to a 1500w amp.  As I said I have had three fail this way.

I use sequencing so absolutely not due to hot switching (at least 
30msec delay before RF applied).

Maybe they will handle HF power better (I do not have HF QRO).  Also 
when running 2m-eme my 8877 is key down for 50-seconds under JT65 and 
key up for 70-seconds, which repeats as long as in transmit.  So this 
is "almost" Alpha brick testing!

When one of the relays shorted I noted that my 8877 output went to 
1800w and drew over an amp at 3000v.  Fortunately I noted this 
quickly and shut it down.  Grid current was higher but apparently no 
harm to the 8877 (what a really tough tube  -- I have eight years 
running on the same tube).  I use a G3SEK Triode Board for bias, 
warm-up delay and overcurrent protection for both anode and grid.

Two coax relays probably work as well as a transfer relay for the two 
amp application.  Make sure the output relay can handle the max power.

I have one surviving CX600NL which is used to select either 1296 amp 
or 900 amp at my tower top (both low power level drive input for the 
amps).  I now use NARDA sem123N (1200w at 150-MHz) in the high power ckts.

73, Ed -KL7UW

From: "Joe Subich, W4TV" <lists at subich.com>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500/KAT500 paired with AL-1500?
Message-ID: <3bc97592-0eac-519c-11c9-2ac21fd49eaa at subich.com>
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A pair of the Tohtsu CX-600NL relays from Surplus Sales of Nebraska
<https://www.surplussales.com/Relays/rfcoaxialrelays/rfcoax_n.html>
should work just fine.  It would likely take a pair of transfer relays
- one on the input and one on the output of the amplifiers to do the
same thing.

The only advantage of transfer relays is that the unused amplifier
could be kept terminated in a dummy load.

73,

     ... Joe, W4TV

73, Ed - KL7UW
http://www.kl7uw.com
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