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Re: [Amps] Relays

To: "'Paul Kelley N1BUG'" <>, "'Amps'" <>
Subject: Re: [Amps] Relays
From: "Tim Duffy K3LR" <>
Date: Sun, 30 Mar 2008 13:14:54 -0500
List-post: <">>
Hello Paul!

The rig delay of only 3 Ms could be a real problem.

We never run QSK, so I am sure that helps prolong the life of the relays in
use at K3LR. The K3LR Icom radios and computer CW keyers and voice keyers
all have small delays that allow the amplifier relays to close properly
before RF is applied, so I am sure that helps as well.

As you point out, radio + amplifier "handshaking is important.

Tim K3LR

-----Original Message-----
From: [] On
Behalf Of Paul Kelley N1BUG
Sent: Sunday, March 30, 2008 1:10 PM
To: 'Amps'
Subject: Re: [Amps] Relays

Thanks Tim,

That is reassuring. I have been using RJ1A relays in my HF single 
4CX1500B for some time and have yet to experience a failure. I run 
QSK CW frequently. I am also using them on my new 6m 4CX1500B amp 
where I realize I'm probably pushing my luck... time will tell.

Recently I was asked to repair an amp using RJ1A relays that had 
suffered contact failures. It wasn't all that much power, about 1 
kW. I became curious as to why the relays had failed. The owner had 
controlled the amp by a simple cable from the rig's amp T/R control 
line to the amp. Unfortunately that rig only had a delay around 3 ms 
after closure of the amp T/R contacts to the start of RF output in 
both CW and SSB. The new RJ1A relays I installed needed 5 ms 
(measured) to close and stop bouncing, so they would be hot switched 
by that setup. Not good. I wonder if this sort of thing might 
explain some of the vacuum relay failures we hear about?

I would add that fast relays can in some cases actually be slowed 
down by the nature of the power supply or the circuit controlling 
them. I always verify actual timing of the relays in an amp with the 
RF output delay of the radio(s) it is to be used with unless there 
is provision for 'RF hold off' handshaking between the amp and 

Paul N1BUG

Tim Duffy K3LR wrote:
> I have been using single Kilovac HC-1 and Jennings RJ1A relays for input
> output T/R switching on all of my single 8877 amplifiers for the past 25
> years. 
> Even in heavy contest operating, I have had no problems at 1500 watts
> up through 50 MHz.
> 73!
> Tim K3LR
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