If Ray has a K3/10, then the power supply is perfectly fine. The recommendation for that is "13.8VDC @ 6A for K3/10”.
There are a lot of K3/10’s in the field. Nothing in his post indicated which transceiver he has. However, if indeed he has a K3/100, then Frank is right (as usual). Ray should probably be using a heftier supply. Margins are important. 73! Jack, W6FB ps Thanks, Frank! > On Apr 15, 2020, at 10:22 PM, donov...@starpower.net wrote: > > Hi Ray, > > > This is probably unrelated to your capacitor failure, but your > "big hulking linear supply" is underrated for the K3 unless you > run your K3 at less than full output power. The RS-20A might > be okay for SSB, but certainly not for RTTY or digital modes at > K3 full rated output power. > > The Astron RS-20A specification: "amperage (continuous) 16 A, intermittent > 20A" > > > www.astrondistributors.com/astron-rs-20a-1667.html > > > The K3 manual recommends " 13.8VDC @ 25A continuous duty" > and specifies: "13.8 V nominal (11 V min, 15 V max). 17-22 A typical" > > > ftp.elecraft.com/K3S/Manuals%20Downloads/K3S%20Owner's%20man%20A1.pdf > > > 73 > Frank > W3LPL > > > > ----- Original Message ----- > > From: "Ray Albers" <rayalb...@gmail.com> > To: elecraft@mailman.qth.net > Sent: Wednesday, April 15, 2020 7:31:23 PM > Subject: [Elecraft] Electrolytic Capacitor failure > > I could use some knowledge and/or opinions on this subject (Radio/Elecraft > related only because it deals with a power supply that powers a K3!) > > The other day I was about to initiate a call, and as soon as I touched the > "dah" paddle the K3 instantly shut off. The cause was that the power > supply voltage dropped too low when the radio demanded more current. > > The power supply is an Astron RS-20A, a big hulking linear supply that I > really like. Huge heavy transformer and two series-pass transistors mounted > on big heat sinks - thus, quiet acoustically (no cooling fan) and > electrically (no RF hash from switching). I have two of these - one that I > bought for my new radio when I got back into ham radio after a long > absence and the other because I was at a hamfest where someone had a pile > of them that he was selling for only $20 each - who could resist? So I > trotted out the spare supply and got back on the air. Now to troubleshoot > the bad supply. > > I had trouble with this one about five years ago. The output transistors > are plugged into sockets, and on one socket the contacts for the emitter > pin had gotten loose, and there was a vicious spiral of heat causing more > resistance causing more heat until eventually it actually melted the > transistor pin and left a black char on the socket. When I replaced the > socket that time, I decided to solder the emitter pins on both transistors. > > It took me a long time to find the problem this time. Various tests told me > the transformer, the full-wave rectifier diodes and the pass transistors > were fine. Finally - with some help from hints in a great article about > Astron supplies on repeaterbuilder dot com - I figured out that the supply > voltage to the regulator board was too low, so there was not enough "oomph" > available to drive the output transistors when high current was demanded. > > This supply voltage comes from a center tapped transformer secondary > feeding two small diodes (both of which checked OK) to a 1000uF 35 V > electrolytic. Turns out the capacitor was bad. It's a typical aluminum case > with blue plastic covering (which I assume to be heat-shrink plastic > because of the way it is completely molded around the capacitor.) > Replacing it brought the supply voltage up to spec, and now everything > works fine. > > But I was surprised about the capacitor failure. Absolutely no visible > signs of anything wrong - no bulging, leaking, etc. And the soldering to > the PC board is perfect. So here's my question for the group: What do we > know about electrolytic capacitor failures? I know that anyone restoring > an old ham transmitter or receiver or BC receiver almost always has to > re-cap it, because the ancient electrolytics, which are usually wet > electrolytics in chassis-mounted cans, will have gone bad. But this is the > first time I've ever had a failure of the more modern type electrolytics. A > quick search of capacitor failure on Google shocked me when I read claims > in several places that these capacitors are only expected to have a two to > five year life!! Can that be? I know I've got lots of radio gear that's > way older than that and still working fine. To do this repair, I replaced a > capacitor that might only be 5 years old with one that is probably twenty > years old! > > Words of wisdom and enlightenment would be most welcome! > > 73 > Ray K2HYD > (K3 #8240, KX-3 #6827) > ______________________________________________________________ > 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 > Message delivered to donov...@starpower.net > > ______________________________________________________________ > 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 > Message delivered to jackbrin...@me.com ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
