[CW] Frank W7IS: THE REAL REASON FOR SPEED KEY DOT STUTTER

Sun May 5 13:33:23 EDT 2019

     I should trim the material below but am not sure how to do 
it without loosing the thread.
    I wonder how the rod the dot return spring is fastened to on 
the Lightening Bug affects the quality and number of the dots 
other than controlling the amount of force needed to actuate the 
dot paddle. It seems to me the pendulum is held tightly against 
the stop while the paddle is pressed. It seems to me that the 
spring can have no effect during the period. I could well be 
missing something.
     The patent for the Original shows an adjusting screw to fix 
the resting position of the support arm for the dampener. I think 
this was done so that the entire moving part of the bug could be 
made straight. However, the equivalent adjustment can be done 
using the pendulum rest adjustment. I may not be using the right 
terms for these parts. Eliminating the adjustment on the dampener 
would save some small amount in manufacturing cost, namely the 
cost of the part and the cost of machining a threaded hole for 
the part. Its interesting that Vibroplex and others were able to 
get rid of both the swinging arm and also the bridge arrangement 
used on the Lightening Bug for adjusting the position of the 
damper. The damper on several bugs, for instance the Bunnell 
J-36, in mounted on a fixed post.
    I think the precise alignment of the dot contacts is nessary 
to dot quality. There are too many adjustments in these keys so 
its easy for things to be out of adjustment and to overlook the 
way the contacts come together. The overall height of the 
pendulum is important. Since the contacts and the point where the 
end of the pendulum strikes the damper are both important one may 
have to resort to both adjusting the trunions and resort to 
shimming the support post for the fixed dot contact with washers.
    BTW, its interesting to look at the motion of a bug using a 
Stroboscope.
    Regarding Frank's comments; one is the design of the earliest 
damper which I have addressed above. Also, he mentions one of his 
  very early keys was coated with gunk he attributes to a coal 
stove. A lot of these keys were in railroad installations and the 
gunk could well come from a coal stove burning the usual soft 
coal used in locomotives or be from just the soot and junk from 
years of exposure to coal burning locomotives. I am just old 
enough to remember when there were a lot of coal burning steamers 
and how appallingly dirty they were. I did live in cabins with 
pot belly stoves a few times but they were wood burning.
     Also, the leather-like finish was probably "crackle" paint. 
This is what Hallicrafters used on the SX-28 and some other 
receivers, and what General Radio used on instruments for 
decades. Its different from "crinkle" finish and is an expensive 
finish because it requires at least two coatings.
    My oldest Vibroples, a 1920 Original, is finished in what I 
think is Japanned enamel. This is a baked enamel finish, smooth 
and quite thick. Mine has gold striping on it.
    Also, I have an early Speedex key, no label nor is there any 
indication that there ever was one. I have the original box but 
part of the label is gone. I think this was a pre- Les Logan key.

On 5/5/2019 8:27 AM, D.J.J. Ring, Jr. wrote:
> I own way too many Mac keys... The Mac Stream keys are unique and a
> hoot to use on the ham bands.
> 
> The Mac key I've tested that had the worst case of self oscillation of
> the dot contact is a black based P500. McElroy might have been the
> worlds best telegrapher but he certainly wasn't much of a machinist.
> Some of the literature he put out stated that each key was
> scientifically adjusted at the factory using Oscilloscopes !!! The sad
> part is he charged extra to equip only a few deluxe keys with the dot
> stabilizer he invented. Leaving such a large number of keys to suffer
> from the self oscillation problem of the dot contact spring assembly.
> But I'm sure he went to the grave never realizing his mistake. One of
> the neat things he did on some keys was to provide a height adjustable
> large dampener wheel. The dampening wheel works best by hitting the
> wheel in a way that forces it slightly upwards. Its too bad all his
> keys didn't provide the height adjustable dampener wheel. When Martin
> invented the very first Vibroplex in 1904, he equipped it with a long
> set screw to adjust the articulated damper travel. But then abruptly
> dropped the feature soon afterwards.
> 
> I own a number of those very first Vibroplex's made in 1905 and 1906
> and the only thing that causes them to be difficult to adjust for best
> code is the main spring he used in those days were too long. And the
> long main springs caused the dot arm to flop around too much on the
> damper. It wasn't till around 1912 that Vibroplex started using
> shorter main springs.. The type of material and length of the main
> spring being critical in how the key makes dots. The highest quality
> main springs ever placed on a speed key were on the WW2 Bunnell J36
> keys. They take more to slow them down but produce the highest quality
> code at any speed. Some keys with weak main springs cant make more
> than 5 or 6 dots in a row.. and cant be adjusted to send over 25 wpm..
> Below is a link to a Blog that I wrote in 2009 about my experience
> with a difficult to adjust Lionel J36 WW2 speed key.. It turned out
> the problem with the key was the metal arm which held the dot coil
> spring in place had too much play.. So you can run into all sorts of
> weird problems with vintage speed keys.
> 
> http://speedkeytests.blogspot.com/2009/02/testing-lionel-j36-ww2-speed-keys.html
> 
> Frank W7IS
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL