I may just have been lucky so far, but with a DEM 6M preamp and converted SB220, everyone has been getting along with the default 8ms delay in the K3 and a stock SB220 relay.
Be aware that relay switching speeds are specified without a snubber diode connected. Adding the diode can greatly extend the release time of a relay. With the limited testing I have done, it seems not all relays act in the same way (i.e. some go much slower, others not so much). In the Dow-key design guide they indicate "A transient suppression diode across the actuating coil can increase the release time of an electromechanical switch by as much as 100 times." There are ways around this with the use of zeners instead of just a diode. Mark n2qt -----Original Message----- From: Don Wilhelm Sent: Sunday, April 29, 2012 10:11 AM To: Gregg Marco W6IZT Cc: 'elecraft' Subject: Re: [Elecraft] PR-6 issue when QRO Gregg, Unless you have changed the open frame relay in the SB-220, it will take at least 15 ms to switch and be clear of the contact bounce. I would suggest you change the stock relay for something faster. 73, Don W3FPR On 4/29/2012 8:55 AM, Gregg Marco W6IZT wrote: > I use my K3 on 6 meters with a concerted SB-220. When using the PR6 > connected to the KXV3 as intended and using the amp, the GaAs FET is > destroyed immediately. My work around was to employ an external TR relay > on > the K3 to switch TX RX, connecting the PR6 to the RX side of the relay and > to the RX input of the KXV3.Using this arrangement has worked fine for the > past few years. > > With E skip season approaching I thought that I would try to resolve this > problem and get rid of the extra RF plumbing. > > My initial thought was the TR relay in the amp might be too slow and RF > was > being reflected back into the K3 during the transition from TX to RX. > After > looking at the K3 block diagram I doubt that this is the case as the PR-6 > should be switched out of the circuit well before any RF is present at the > output. > > For reference the TR relays in the amp are spec'ed at 8 msec to switch and > the K3 is set at 8 msec TX delay, which I believe is the default. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
