{Collins} Fwd: Re: KWM-2A problems and tubelore question



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Reply-To: "Rocco Lardiere" <lardiere@xxxxxxxxxxxxx>
From: "Rocco Lardiere" <lardiere@xxxxxxxxxxxxx>
To: <bob@xxxxxxxxxx>
References: <20041024180618.74180.qmail@xxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: {Collins} KWM-2A problems and tubelore question
Date: Sun, 24 Oct 2004 21:11:20 +0100
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Bob,

Welcome back.  You will enjoy the KWM-2A.  Here's what I did with mine when
I bought it a few years ago:

Clean the switches, relays (including the one in the final compartment -
remove the shield from the bottom nuts), connectors, crystal pins, and tube
pins with DeOxit D5 cleaner (Antique Radio Supply).  Apply to metal only on
the fiber switches, if you can.  Try not to let it soak into the fiber.
Then exercise all the switches, etc.  Sometimes the bottom shields around
the bandswitch sections can become less than perfectly grounded, and that
can cause weird oscillation problems, esp on 3.5 MHz.  Cleaning and
reseating the aluminum shield sections is the recommended solution to this
common problem.

As for tubes - I substituted as needed.  At least you can swap between rigs.
I have a box of tubes and sometimes substitute several.  Tube checkers are
good, but nothing beats a known good sub.  Once you have one of the rigs
running well, you can always refer to it.  Use original 6146's, not A's or
esp B's.  W's sometimes work well.  Blue glows don't sound good, but use a
sub to be sure.  Antique Radio has the tubes at a reasonable price.

Perform an alignment per the book.  Do not skip anything, and follow the
directions.  Yes, if you know exactly what you are doing, you can tweak the
caps with the finals enabled - but it's easier to just follow the directions
unless you are very comfortable with the risks to the final tubes.  I
learned that it's best to do exactly what they recommend and don't cheat.
In the long run, you will save time by being thorough.

Hope this helps.  You should be able to achieve full output, all bands, no
funny oscillations.  As for Z5, it is a birdie nuller.   You should be able
to hear a bird at 7.045 and be able to null it out (see p. 5-12 of the
militiary manual).  It should not affect the frequency of the received
signals, esp on other frequencies.  If it does, you have some other problems
not associated with Z5.

73,

Rocco N6KN
----- Original Message ----- 
From: "Robert Stewart" <bob@xxxxxxxxxx>
To: <collins@xxxxxxxxxxxxx>
Sent: Sunday, October 24, 2004 7:06 PM
Subject: {Collins} KWM-2A problems and tubelore question


> Hello to the group.  I have returned to Ham Radio
> after an almost 16 year absence and decided to get the
> radios I wanted the first time: Collins.  Of course, I
> bought them from ebay with the predictable result: one
> works pretty good and the other has problems.
>
> My background, I used to have an Advanced class
> license, and I taught electronics in the Air Force, so
> I have a fair amount of technical skills.  Plus, I
> built several Heathkit rigs and did some homebrewing
> back in the day.  I've returned to Ham Radio with an
> Extra this time.
>
> My questions;
>
> My KWM-2A has a self oscillation somewhere.  When I
> tune Z5, its frequency changes.  Any ideas where to
> start?
>
> Next: in section 4.5.1.2 of the instruction book, it
> says to disable the screen circuit before proceeding
> with the 455-KC IF alignment.  Is this really
> necessary, or is it sufficient to simply bias the
> finals past cutoff?  I'm guessing that the real
> purpose behind removing the screen voltage is to just
> prevent overheating the finals while messing with T1
> and C54.  What's SOP here?
>
> Finally, I've forgotten most of my "tubelore".  I also
> have a KWM-2 which works pretty good.  But, both rigs
> have one tube (different on each) that glows blue.  In
> one, it's V13.  In the other, it's V3.  Swapping both
> out doesn't fix the problem.  Is this a sign of some
> voltage or drive problem that I need to address.
>
> Thanks in advance,
>
> Bob, AE6RV
> Sponsored by the Collins Collectors Association
http://www.collinsradio.org
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>




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Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
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