[Milsurplus] Command Set Transmitter Keying

[J. Forster]

It is possible that surface corrosion or oxidation could cause a effective
thinning of the spring reducing the spring rate.

When you bend a beam most of the stress is carried by the outer layers, so
the most vulnerable layers are the outside. In fact, the central third of
a beam can often be removed without materially affecting the beam's rate.

As to the M1 springs, I'd doubt is has a design life of anything like the
number of operations a relay. As fatigue sets in, the spring rate will go
down.

If the relay coils are all in parallel:

+28  ----/ o-------------------------------
         key    |      |      |     |      |
                K1     K2    K3    K4      Radded
                |      |      |     |      |
GND  --------------------------------------

Adding a resistor at Radded will SLOW the collapse of the magnetic fields
in the relays. The the time constant of a R-L circuit is L/R; w/o Radded,
the R is infinite, except for arcing at the key.

-John

==========

>>Interesting theory, but I'm not so sure a spring would weaken over time.
>
> Perhaps not, John.
>
> But, in a different arena, it's fairly well documented that springs in
> firearm magazines that have been left loaded for long periods of time
> often show degradation.  Also, I had to replace a 60-year old operating
> rod spring on a M1 rifle due to it exerting below normal compression
> force,
> causing cycling problems.  If properly designed, these critical springs
> should not have been exposed to stress past the elastic limit.
>
> I was also part of a incident investigation for loss of a 1100 megawatt
> electric nuclear plant's output when a voltage regulator swap from auto to
> manual mode failed.  The opening spring force in the mode switching relay
> was found to be insufficient to make the normally closed contacts wipe
> and conduct upon de-energization.  It had been OK earlier in its life.
>
> So, who knows?  I don't rule out much when I first examine a condition.
> I would *initially* consider everything that *could* delay K52 drop out.
> One could even look at other mechanical issues, such as corrosion effects
> on
> the armature pivot bearings or coil varnish adhesion to the armature.  All
> are very unlikely for K52...all are effects that couldn't cause the
> consistent
> timing problem reported.  But still, if there isn't something pathological
> going on, then this characteristic of the transmitter HV being applied
> for 30 mS after the antenna has been disconnected was occuring 70 years
> ago
> as a simple consequence of the design.  That extra 30 mS of transmitter
> operation after each key opening is about half the length of a dot sent at
> 20 wpm, the command sets were extremely rarely and irregularly used on CW,
> and a station well removed from the transmitter would not hear that extra
> 30 mS bonus warble due to the opening of the antenna relay.  Perhaps this
> has
> occurred since command set day one.  It's just hard to accept.
>
> So, assume that the old K52 is functioning today exactly as when it was
> new.
> An interesting experiment would be to install an appropriate resistor
> across
> K52 coil terminals (thus across through some wiring resistance the coils
> of K51, K55, K1, K2, and K3).  I'd try something around the 400 ohm K52
> coil
> resistance.  Only a 2 watt rating is required.  If it would dissipate the
> inductive energy of the six parallel coils quickly enough to let K52 (HV)
> drop out before K55 disconnects the antenna, then this would be a cheap
> and
> simple corrective action that doesn't require blocking diodes.
>
> Mike / KK5F
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