Hi Don,
You are absolutely right about it being C31 that required the
change, and that indeed was the one that I did change
. I made the mistake in my note by looking at the circuit I have all the
mods shown on and picked the wrong one to mention.....DUH.
Thanks for picking that one up...
Cheers....Ron ZL1TW
----- Original Message -----
From: "Don Wilhelm" <[EMAIL PROTECTED]>
To: "Ron" <[EMAIL PROTECTED]>
Sent: Tuesday, September 11, 2007 7:15 AM
Subject: Re: [Elecraft] Grounding gear
Ron,
It is C31 that must be increased to .2 uf or larger (.22 uf is the proper
value), not C46 as you stated.
Was that a typo or is that a possible cause of the problem?
I do not think grounding the K2 will help. Yes, without the change to C31
the amp can oscillate - at about 660 Hz. Look at the path through the new
inductors (15 uHy) and series capacitors (4700 pf) through the T/R switch
and you will see that, save for C31 acting as a bypass, there is a nice
series resonant path from output to input, and it is resonant at about 660
Hz. C31 must be increased to act as a good bypass at the 660 Hz
frequency.
73,
Don W3FPR
Ron wrote:
Hi gang,
I know grounding has been flogged on this Reflector before
but I have a question to ask the collective about a problem I have
struck.
A while ago, I managed to convince an interested party to buy a second
hand K2/100 complete with KAT100, that came on the market at a good
price. I knew the set as I had built it myself and had every confidence
in it, however not long after the new owner took delivery, I received a
report that it had gone "bang" and smoke had come out of it, and it
wouldn't work anymore on the KPA100. The amplifier was sent up to me and
it was found that 2 of the T/R 1N4700 diodes were short-cct...the smoke
had been provided by R40 burning out.
The amplifier had been previously been bought up to the latest specs, but
C64 hadn't been changed to the larger value now specified, so I suspected
that must have been the culprit. I replaced the diodes, resistor, Cap,and
ZVN4424's (just in case) and tested the amp as OK on anything I had here.
The amp was returned and has run for a month or so, until I received
notice that it was playing up again.
The problem arose on the same antenna as before, which is a 40/20m
vertical, that apparently the KAT100 has always had a bit of trouble
finding a match on, and once again, when TUNE had been initiated, all the
LED's on the ATU lit up and the set locked up.....it was apparently tried
a couple of times before the fuse in the 13.8v lead blew. It sounds to me
like RF feedback upsetting the rig and causing the amp to oscillate?
Now.....in this particular shack, the chap does not ground his gear, but
rather uses counterpoises on his long wire ( connected to where I am not
sure) and radials on the vertical ( which I presume are above ground as
it is a roof mounted vert), but no ground wire connected to the K2/100 or
KAT100.
Am I right in assuming a "ground" connection on the K2 "may" help? (
Elecraft provide the terminals?)....I would have imagined the set
shouldn't "take off" under any reasonable circumstances, but when RF
feedback (as I suspect) comes into the equation anything can happen.
Any ideas??
Regards.....Ron ZL1TW
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