And I might add that the first paragraph of that same application note explains the 'why' - I quote: "This modification protects the K3's audio amplifier if either speaker output is connected to a short circuit or very low impedance load. Two 470 ohm, 1/4 watt resistors are added to the output circuit to suppress potentially damaging voltage spikes that might otherwise occur."
A mono jack *will* short out the right channel. 73, Don W3FPR Tom Hammond wrote: > Older K3's were susceptible to damage if a MONO plug was inserted into > the STEREO jack on the back panel. Subsequent to that, there was both > a hardware and a software mod to new(er) K3s to eliminate the threat of > damage from that happening. > > UNfortunately, I cannot quote book, verse, and phrase of exactly when > this 'factory' change occurred. I believe it's spoken to in the K3 > Mods section of the Elecraft web site... QRX... lemme check... OK... > here's the info from http://www.elecraft.com/K3/k3_app_notes.htm and down > at "K3 AF Output Mod Kit. Rev C": > > This modification is needed for all K3s shipped approximately > before 01/12/09 containing either a Revision "XB" or Revision > "A" KIO3 board. You must inspect the KIO3 board to see whether > the modification has been made. Modified boards will include > the leaded resistors. You can see one of the resistors by > removing the top cover and inspecting the side of the KIO3 > board facing away from the rear panel. Photos of what the added > resistors look like are in the document. > > Hope this helps. > > 73, > > Tom Hammond N0SS > > > At 15:12 01/03/2010, Keith Hamilton wrote: > >> Doesn't the manual state that a mono plug is ok? I better unplug my speaker. >> I must have read wrong. Thanks a lot for the post! >> >> Keith W8GX >> >> >> On Jan 3, 2010, at 3:57 PM, Dave Perry N4QS wrote: >> >> >>> Tony, >>> >>> Same thing happened to me when I plugged my Kenwood mono speaker into the >>> stereo speaker jack on the back of the K3. I did this without >>> >> thinking from >> >>> the front of the radio when I was rearranging equipment in the shack. The >>> speaker worked for a couple of days until the audio output transistor >>> failed. I could then only hear audio from the headphones. I had >>> >> to send my >> >>> K3 back to Elecraft in order to replace the audio output >>> >> transistor. It was >> >>> under warranty so they repaired it for free. > ______________________________________________________________ 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
