Well, yes, I've had a few transistors fail, too. I remember in 1973 my
Heathkit AR-19 Receiver (AM-FM-Stereo) started distorting as it warmed up. I
held an ice cube against the various transistors in the chain until I found the
culprit, and replaced it.
In my career I even spent one year in Failure Analysis, delidding and depotting
transistors and ICs and peering at them with the SEM.
In my post I was really just facetiously shilling for the K3KU circuit and my
hoard of early-1960's transistors. I'm sure opto-isolators are a fine
solution. I just don't happen to have any on my junkbox.
73, Art K3KU
----- Original Message -----
From: Dennis Vernacchia
To: Art Boyars
Cc: cq-contest@contesting.com
Sent: Wednesday, November 12, 2008 3:34 AM
Subject: Re: [CQ-Contest] CW Keying Cable
I have had several transistor types fail over last 13 years
No failures with the Opto type circuits
No keying problems
( W1GEE Opto units )
U got lucky
others mileage may vary
stick with the Opto units
My 2 cents
N6KI
On Tue, Nov 11, 2008 at 12:08 AM, Art Boyars <art.boyars@verizon.net> wrote:
N6KI said "Be sure the one U buy uses an Opt Coupler typr device and not
descrete transistor(s) - The Optos are far more reliable !!!"
Gee, the 2N398A germanium PNP and the whatever NPN used in the original
implementation of the "K3KU circuit" for keying pos or neg have been in use for
over 30 years w/o failure. They may well pre-date optocouplers AND computer
keying.
I still have a few 2N398A's if anybody wants to build the circuit, though the
MPSA92 used by Logikey in their CMOS4 and by MFJ in their 490 would work fine.
(Note that Logikey and MFJ both use it as a separate neg keying output, not the
K3KU circuit.)
73, Art K3KU
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