Hi all, I am from the old school of thinking that sometime I am going to need to key an AC relay in an amplifier and prefer to make a VERY simple interface and generate a set of dry contacts. That way regardless of the keying gender, you are safe. It keeps ground current loops out of the picture too.
Mel K6KBE --- On Sun, 8/31/08, Tom Hammond <[EMAIL PROTECTED]> wrote: From: Tom Hammond <[EMAIL PROTECTED]> Subject: RE: [Elecraft] SB-221 for K3 need some help. To: [EMAIL PROTECTED], "'Don Rasmussen'" <[EMAIL PROTECTED]>, [email protected] Date: Sunday, August 31, 2008, 10:10 AM Hi Joe & Don: > > I found out this week that K3 is good with Heathkit > > SB-220 amps, all you need to do is connect a shielded > > RCA cable between the units - how easy is that? !!! > >Are you sure? Most of those amplifiers had high voltage PTT >circuits. If I recall correctly the TR relay is a 120V 3PDT >unit. You may need a buffer or soft-key circuit in your >amplifier to make it safe with the K3. The T-R output MOSFET in the K3 is rated at 200VDC at around 5A, so it should not be much of a concern for switching. Additionally, the MOSFET is diode-protected against reverse spikes from the relay it's keying. HOWEVER... this having been said, were it me, I'd add an (internal) Lo-voltage keying interface, like that offered by Harbach, to change the T-R keying voltage presented by the SB-221 from 120VDC to around 2VDC and maybe a couple mA of current. Pretty economical and easy to install, and worth the effort to install. Any T-R keying interface regardless of what you use (OEM or 3rd party) will not, as Joe has pointed out, change the keying speed of the open- frame T-R relay. That is a separate problem which CAN be addressed with replacing the OEM relay with a high-speed power reed relay (drive input) and a vacuum relay (RF output). But you CAN significantly improve the transition speed of the relays IF you NEED the feature. 73, Tom N0SS 73, Tom N0SS _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
