|[AMRadio] NCL-2000 and SR-2000 band switch issues|
hallicrafterssr2000 at k9axn.com
Thu Oct 2 14:31:36 EDT 2014
Disclaimer: I have never seen, owned, or worked on an NCL-2000. None the
less, if you read this with an open mind, you will at least find it
interesting and at best will provide a fix for the most troublesome failure
in the NCL-2000.
The band switch on the NCL-2000 was originally made by OAK using coin silver
or spring hard sterling for contacts and rotor wipers, not silver plated
copper. The new Chinese switches are silver plated copper with slotted
contacts --- Beware.
If you observe the original contacts they are solid not slotted surface.
Further, they were rated at slightly over 12 amps and the configuration used
a pair of contacts combined for 24 amps. The design by OAK assumed safe use
at up to 150% of design criteria. The current carrying capacity of that
switch is quite adequate for the 2KW transmitters that used them,
specifically the NCL-2000 and SR-2000. The notion that the current carrying
capacity of this switch is inadequate for these amps is misguided. The only
way to exceed the switch limits is to run AM in high power mode. Of course
doing so is a bit feeble minded and proves that survival is for the fittest.
Do a bit of analysis. How many have failed when using the 80, 15, and 10
meter bands? Very few and that was likely operator error.
The 40 and 20 meters bands comprise the majority. Why is that? The post
mortem reveals the source of the malady. The front wafer is almost always
the apparent starting point with the arcing propagating to the rear wafer.
In that the front wafer carries less current than the rear and is usually
the point of failure, doesn’t it suggest that current is not the culprit but
voltage arcing is responsible?
The SR-2000 uses the same front wafer design and the A level radio had the
same frailty. The Hallicrafters engineers had the financial resources to
fix the problem and all of the release level trials verified the cause,
voltage arcing!! . I am certain that the National engineers became aware of
the problem early but were in too much trouble financially to fix it. It is
also very apparent that the service people knew that there was a problem but
were oblivious of the cause.
The first redesign by Hallicrafters engineers improved the failure rate
dramatically and the second eliminated the problem, yes using the same
switch. There you are, the switch is not the problem but the configuration
is. The first redesign occurred in 1967 and the second 1971 four years
later, about the same time that production ceased.
It is inappropriate to fault the National designers because every power
engineer at the time using the switch for the same purpose made the same
error. The switch was appropriately designed to support the application ---
just incorrectly configured.
The standard National front wafer can be refitted using the same components
to equal the first redesign by Hallicrafters and with some thought the
second and final design by the Hallicrafters engineers.
There is a lot more to this story and if I could put my hands on a
functioning complete switch I can write what has to be done to replicate the
first redesign and the second. If you have one and can temporarily part
with it, send it out and I’ll write a yellow brick road paper. Then maybe
the NCL-2000 switch legend can go to sleep. The SR-2000 has been reconciled
I solicit questions and conversation but if you feel belligerent please don’t
Kindest regards Jim K9AXN
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