Andy K3WYC commented that there have been reported failures of R7, D8 and D9, and maybe other components. Does anyone have a root cause analysis for these failures?
I can see why Q5 was changed from a FET to a Darlington NPN: the 5T voltage is marginal for turning on the FET. But why was R3 changed to a zener diode? Are there huge voltage spikes on the 5R line? Thanks, Alan G3XAQ Andy Durbin via Elecraft <https://www.mail-archive.com/[email protected]&q=from:%22Andy+Durbin+via+Elecraft%22> Sat, 06 Jun 2026 11:33:46 -0700 <https://www.mail-archive.com/[email protected]&q=date:20260606> wrote :- My notes on TR switch R7 include - "Several reports of R7 failure some also with failure of D8 and D9. Results in approx 20 dB RX signal attenuation when BYP compared to OPER." The voltage of almost every component junction in the TR switch were researched and documented here - https://www.qsl.net/wb4kdi/Elecraft/KPA_TR.html Click on the schematic links for the two TR switch states. More info on KPA500 at the parent level - https://www.qsl.net/wb4kdi/Elecraft/ This is a great KPA500 resource and is being maintained. Please contribute if you learn something new. 73, Andy, k3wyc -- Alan Ibbetson [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
