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Re: [Amps] Relays

To: "'Paul Christensen'" <w9ac@arrl.net>, "'amps'" <amps@contesting.com>
Subject: Re: [Amps] Relays
From: "Alex" <alexeban@gmail.com>
Date: Wed, 2 Apr 2008 22:30:32 +0300
List-post: <amps@contesting.com">mailto:amps@contesting.com>
They DO have a reliability problem. Don't forget  that the OFF diode has to
be back biased by at least 3 times the RF voltage at the relevant power
level: that means approximately 800V at the 1kW level and this without
taking the higher SWR's into consideration! The real rugged ones _ like
those manufactured by Chelton Microwave-  are specified at up to 3000 bias
for high power operation. I wouldn't lie to have to add such a source and
think that you have also to switch it! Not so easy, believe me! I'd bet for
vacuum relays any time for QRO use!
73,
Alex

-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Paul Christensen
Sent: Wednesday, April 02, 2008 5:33 PM
To: amps
Subject: Re: [Amps] Relays

> Alpha began using PIN diodes later in life, did they not?
> Any reports on that picture of reliability?

I can't comment on the failure rate statistics, but I can tell you I have a 
real love-hate relationship with high-power PIN diodes.  I know that they 
will not hold up as well as a vacuum relay under adverse operating 
conditions (e.g., certain points on the SWR circle).  On the other hand, I 
have an Alpha 86 with PIN diodes that has performed exceptionally well under

some pretty harsh conditions and I've not yet experience a failure. 
Probably for resonant or near-resonant antennas under a 2:1 VSWR, they are 
fine.  And, as ling as the SWR protection circuitry is paying attention, I 
am not sure why the diodes fail unless they are being operated at full power

at a VSWR of 2:1 for extended periods of time with modes like RTTY.

I like the robust design of vacuum relays, but I also like the completely 
silent switching offered by PIN diodes.  I do see that Alpha has just 
released a PCB for the 86 that replaces the PIN diodes with a Jennings RF-1 
vacuum relay.  It's a 100% drop-in replacement for the existing T/R board. 
Cost of the board alone is $500.00 from Alpha.  I plan on ordering one to 
keep on the shelf, but I have every intention of keeping the 86 in stock 
condition for as long as possible.

My current Alpha amp line-up consists of a 77Dx, 70V, and 86.  The 77Dx uses

a Jennings RJ-1, while the 70V uses a Jennings RF-1.  Neither relay has 
required replacement and the RF-1 is now 38 years old and has definitely 
worked for a living.

Paul, W9AC 

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