[Elecraft] Grounding gear

[Ron]

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" <w3fpr at embarqmail.com>
To: "Ron" <ron_w at clear.net.nz>
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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