[Elecraft] KPA100 SO-239 Help

[Wes Stewart]

All good stuff.  My K3 exhibits erratic power output at times, (TX Gain failure) corrected by loosening and retightening the screw that threads into the 2D block and standoff next to the SO-239.  Relying on aluminum-to-aluminum mechanical connections for r-f returns is bad business.

Next time I'm in the mood I will apply Paul's fix.

Wes  N7WS

--- On Fri, 2/25/11, Paul Christensen <w9ac at arrl.net> wrote:

> From: Paul Christensen <w9ac at arrl.net>
> Subject: Re: [Elecraft] KPA100 SO-239 Help
> To: elecraft at mailman.qth.net
> Date: Friday, February 25, 2011, 11:48 AM
> 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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