http://elecraft.85.s1.nabble.com/Electrolytic-Capacitor-failure-tp7659760p7659783.html
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.
> On Apr 15, 2020, at 10:22 PM,
[hidden email] 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" <
[hidden email]>
> To:
[hidden email]
> 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:
[hidden email]
>
> This list hosted by:
http://www.qsl.net
> Please help support this email list:
http://www.qsl.net/donate.html
> Message delivered to
[hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home:
http://mailman.qth.net/mailman/listinfo/elecraft> Help:
http://mailman.qth.net/mmfaq.htm> Post: mailto:
[hidden email]
>
> This list hosted by:
http://www.qsl.net> Please help support this email list:
http://www.qsl.net/donate.html> Message delivered to
[hidden email]