[Elecraft] KPA100 SO-239 Help

[Paul Christensen]

One solution, especially for folks who are in the beginning stages of K3 
construction, involves substitution of the SO-239 for a better quality 
connector.  I used a pair of Amphenol types with a Teflon insulator, but 
Phenolic is fine.  These were purchased from Mouser, catalog P/N is 
523-83-798.  The Amphenol P/N is 83-798.

On a  related matter, I avoid RF return path connections where only the 
chassis is used to establish an RF return without a dedicated return wire. 
Without a return wire, the return path is often left to force its way 
through multiple mating metal pieces and hardware.  On my K3, I added a 
dedicated ground lug and buss wire connected to the SO-239's machine screws. 
The other ends are connected back to the PCB, adjacent to the center pin 
wire. On a different mail list, this sparked debate as to whether this 
practice creates a "PIN 1" problem.  It doesn't.  The buss wire is used back 
to the RF circuit but it's not a substitute for the SO-239 bonding still 
desired at the chassis.

What's odd is that the KPA100 assembly manual as shown on p.32 (Figure A2) 
shows use of a ground lug and buss wire on the SO-239 connector back to 
circuit ground.  The oddity is that this practice was not carried through on 
the K3.   Apart from the chassis, it seems the only ground return connection 
available on or near the SO-239 is if the Aux  RF BNC connector is 
installed.  Then, the shield of the RG-174 coax ties to a ground lug.  For 
reference, see p. 24 of the K3 assembly manual.

Paul, W9AC

----- Original Message ----- 
From: "Jack Smith" <jack.smith at cliftonlaboratories.com>
To: <elecraft at mailman.qth.net>
Sent: Friday, February 25, 2011 1:08 PM
Subject: Re: [Elecraft] KPA100 SO-239 Help


> I've found the same problem with two batches of Teflon insulated, single
> hole mount SO-239 connectors manufactured in China and purchased from RF
> Connection. The center pin spins within the Teflon bushing and unless
> the user is extremely careful when connecting a PL-259, the wire
> connected to the center conductor will break off.
>
> I returned one batch and received a second batch that were supposed to
> be correct and found the same problem. I rejected those as well.
>
> I agree that a connector with this problem should not be used - too
> great a risk of damage to the internal wiring.
>
> Jack K8ZOA
>
> On 2/25/2011 12:58 PM, dw wrote:
>> Hi John,
>> If it were me, and there is a possibility that the inner wire soldered
>> to the inner pin could freely spin around during the process of taking
>> on/off coax at the back of the unit, I would not take the risk of
>> compromising the inner wire such that it could twist, bird-cage or
>> possibly short to gnd.
>>
>> N1BBR
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