[Collins] [Fwd: Re: KWM-2]

[Dr. Gerald N. Johnson]

I had the same question from Dave Knepper 5 weeks ago, off list. I made
the following suggestions and haven't heard back. I'm sticking with the
idea of one transmit slug on the bottom side of the coil with all the
rest on top. It would be possible to track the other bands that way
since each has a variable trimmer. I'd look to see, one coil at a time
if there was a peak spot with the slug retracted further than the one
its peaked on now. I'd also check to see if a slug had been replaced
with one having a higher permeability or a longer wire between the screw
and the slug or had the slug reattached to the wire but with the wire
not at the bottom of the hole in the slug.

Otherwise there's always a possibility of a bandswitch contact problem
or a weird ground problem with a tube socket or shield, though those
ground problems should show up problems more universally.

Another thought. There are some small molded RF chokes with signal
across them. Like L6, L7, L12. The 2mh are so small they have to be
ferrite core. A cracked core or shorted turn would lower the inductance
and show the greatest effect on 80 meters. A replacement from a
different vendor could have a series resonance near 80 meters to reduce
the Z. Any RF choke used in those applications needs to be checked for
that series resonance in ham bands or it can cause gain problems.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer

-------- Forwarded Message --------
> From: Dr. Gerald N. Johnson <geraldj at ispwest.com>
> Reply-To: geraldj at ispwest.com
> To: david knepper <collinsradio at adelphia.net>
> Subject: Re: KWM-2
> Date: Tue, 27 Jun 2006 09:47:43 -0500
> On Tue, 2006-06-27 at 06:56 -0400, david knepper wrote:
> > Jerry, I trust that you are well and enjoying this nice weather.
> > 
> > I have a question for you:  I am working on a KWM-2A and just cannot seem to 
> > get sufficient grid drive or output on 75 meters.  Let me explain further...
> > 
> > I do a complete realignment on 3800 KHz but when I go up the band to 3.9 or 
> > 4.0 MHz, there is virtually little output.  When I  realign the slug tune 
> > rack and the same results.  It seems that the I can get very little output 
> > even if I do a realignment at 4 MHz.  The output is relatively normal at 
> > the bottom end or at 3.8 MHz.
> 
> So you are using the same crystal from 3.8 to 4 MHz? Tosses that out.
> Also keeps the bandswitch out of the problem. A broken slug? So that
> part stays down while the rest moves? 
> > 
> > On 40 meters, I do not experience this condition.
> 
> That's hard on the broken slug idea.
> > 
> > What is funny is that the rig works perfectly on receive.  With the 100 KHz 
> > crystal marker on, the slug tune rack peaks the signal in each of the 100 
> > KHz increments: 0, 100, and 200.
> 
> The transmitter side of the slug rack tunes more stages than the receive
> side while the oscillator is the same for both.
> > 
> > I did install another set of 6146 tubes and a new 6CL6 driver tube.
> 
> And you redid the driver, PA, and feedback neutralization?
> 
> How about the broad IF alignment? Mixer balance?
> > 
> > Thanks
> > 
> > Dave, W3ST
> 
> Mixer gain is dependent on LO drive. All mixers.
> 
> Maybe a slug is just past the center of the coil on 80 meters so its
> tuning the opposite way from the rest. Might look for a slug peak on 80
> with the slug retracted towards the rack.
> 
> I'll probably think of more later but these are few ideas, some not so
> obvious.
> 
> 
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer