Re: {Collins} KWS-1 Output Problem

Vince,  Have you re-neutralized the transmitter Driver and PA.   The circuit
that Collins originally put in there was designed for the 4X150s and when
the change came originally from 150 to 4CX250s, the neutralization was still
functional although the tube inter-electrode capacitances were somewhat

When the "improved" 4CX250B came out, the inter-electrode capacitances
changed again and most KWS-1 neutralization networks would not get the job
done.  The PA neutralization can be brought back "in range" by a
non-destructive careful modification of the Plate Butterfly capacitor.

This problem and the change and then alignment is described in my Care and
Feeding of Your KWS-1 article.  This is available on our website for
download for free in both the RX fir Your Collins Section and also a link on
the front page.

Even if you think that you neutralized it, if that slider for the
Neutralization cap is all the way at the top, you are in trouble.

I suggest you get this and read it carefully and then proceed. You should
not run that PA without neutralizing it correctly and then checking on a
Spectrum analyzer all across all bands.

Good Luck.


Bill Carns, N7OTQ (Trustee K0CXX)
Current CCA Board of Directors
Past President, Collins Collectors Association
Founding Board, Collins Radio Heritage Group
Editor, Signal Magazine (Retired)
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)

-----Original Message-----
From: Collins [] On
Behalf Of Vince Vielhaber via Collins
Sent: Wednesday, May 08, 2019 9:35 PM
To: Collins <collins@xxxxxxxxxxxxx>
Subject: {Collins} KWS-1 Output Problem

Back around '77 I bought my Golddust Twins w/ accessories from the original
owner.  Included were the original 4X150 finals.  He did all the updates to
both the transmitter and receiver as they came out.

Sometime after I got it the 4X250s went out and when I replaced them with 2
new 4CX250Bs I had problems getting any output - even after alignment.  So I
put the 4X150s in and it had worked fine.  I figured there was either
something wrong with the tubes or CX weren't compatible.

The 4X150s worked fine for a number of years.  At some point, I my antenna
came down (long story, babysitter, kite, ...) and I never got it back on the

Fast forward to now.  25-30 years went by and I didn't run the transmitter
and only sparsely used the receiver.  Needless to say many caps had dried
out in both.

Got the receiver working good now but the transmitter is giving me some

After the power supply rebuild I have the all the supply voltages working
right, loaded it up (with the 4X150s) and got around 700 watts on 80 meters

Not wanting to keep the 150s in there, I put a fresh set of NOS 4CX250Bs in
it.  At the time I had forgotten why the 150s were in it until after I went
thru the alignment. I used the W8MAQ neutralizing method and when I was done
with the alignment I loaded it up on 15 meters.

Loaded up nicely to 500ma, I looked at the wattmeter and it says 40 
watts.  Huh?   Tried a different wattmeter, also 40 watts.   Tuned up on 
80 meters, once again 500ma and once again 40 watts out (CW).

Supply voltages are good except the TUNE voltage is low.

I looked at the output of the transmitter on a spectrum analyzer and all it
shows is the one signal.

I bypassed the TR relay, no difference.  Yes, I'm using a dummy load.

What am I missing?

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