[Johnson] T/R relay

[Carl]

Most all commercial ham amps in the 1000-1500W range use open frame DPDT or 
3PDT relays in the 10-13A contact range.

Since the Johnson Desk is capable of 3000W PEP on AM I would suggest a relay 
with 15-20A contacts and use a capacitor to compensate for the XL bump on 
10/15M.

The readily available vacuum relay such as the RJ-1A or equivalent is SPDT 
so you will either need 2 of them or a small relay on the input that is fast 
enough. My amp uses a regular DPDT DIP relay with the poles in parallel and 
a sequencer that allows 50 wpm QSK without hot switching but I stick to 
20-30 wpm of VOX CW and SSB and it has held up since 1986.

Perhaps the simplest approach is the Johnson 250-39 Electronis T/R switch 
which is rated to 4000W PEP. I havent run mine beyond 2000W PEP on AM and 
its none the worse for wear.

Carl
KM1H




Subject: Re: [Johnson] T/R relay


On HF, a generic open frame relay with at least 5-amp contacts, can take 
full legal power (and then some).

Look inside of many linear amplifiers and one will see relatively small open 
frame relays used for antenna switching.

Glen, K9STH


Website:  http://k9sth.com


________________________________
 From: Bill Cromwell <wrcromwell at gmail.com>
To: johnson at mailman.qth.net
Sent: Wednesday, July 10, 2013 12:26 PM
Subject: Re: [Johnson] T/R relay


On 07/09/2013 01:24 PM, Jimmy Green wrote:
> I am setting up my 75A4 and Johnson Desk KW. Please someone tell me should 
> I use a Dowkey or a Vacum relay.If vacum, tell me how to size and how to 
> connect. I know nothing about the vacum relay.
> Thank you in advance.
> Jimmy K5CSU
>

Hi,

I'm waiting to hear about that, too. I have not needed a vacuum relay
because I have never used more than about 100 watts. So what power level
is beyond open frame relays?
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