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W0EB's Dot Stabilizer

For Semi Automatic (Bug) Keys. Design Copyright (C) by Aubrey J. Sheldon, W0EB 2014-2022, All Rights Reserved


Right handed Dot Stabilizer mounted on a late model Vibroplex Original


Back in the early 1930's, T.R. "Ted" McElroy (Morse copying World Champion, set 75.2 WPM record on July 2, 1939) who also manufactured telegraph keys, came up with a nice innovation he called his "Dot Stabilizer" This nifty little gadget pre-loaded the vibrating dot contact spring by a very small amount, effectively ensuring better dot weighting and came very close to completely eliminating the very rapid contact bounce occuring when the contacts wipe together as they "make" which creates what many call "scratchy dot syndrome".

I was originally under the impression that this bounce was being caused by excess dot contact vibration as the contact "break" occurred, but after quite a bit of research and oscilloscope analysis by myself and one of my users (pictures of the traces later on this page), I have finally realized that it's caused mainly by improper contact alignment, minor imperfections in the contact surfaces of both the fixed and movable dot contacts that do not allow for near perfect mating of the two contacts as they come together and the fact that the movable contact is actually on the end of a spring that is really free to vibrate as the contacts come together during the forming of the dots.

In a perfect world, the factory would achieve perfectly smooth surfaces and perfectly square alignment of the two contacts, but we all know this is really asking too much of them, and the average individual either doesn't have the tools, expertise or patience to achieve this either. Mr. McElroy evidently figured this out and came up with the original "Dot Stabilizer" as he called it.

The DS stops the spring from bouncing too much as they come together at the beginning of the dot. It allows setting this "make" tension at an exact and adjustable point,and this comes very close to completely stopping that "contact wiping" bounce which appears to be the root cause of "Scratchy Dot Syndrome". It does not, however, correct bad CW caused by poor sending habits or failure to keep the bug's contacts clean.

T.R.'s original version required replacing the existing dot contact assembly with his stabilizer and fit only the McElroy manufactured keys. For some unknown reason, most information on the original Dot Stabilizer was either lost or ignored during the WW2 years and later except by a very few people. I'm quite happy that I was able to resurrect something from the past that does such a nice job of making a bug able to send better CW without having to severely modify a nice key.

Many people have used a bit of foam stuffed between the loop of the movable dot contact to stop the "scratchies" but it requires periodic replacing as the foam tends to crumble over time. I got a bug at a hamfest that had the foam solution a few years ago and after reasearching the reason for the foam, I found out about T.R. McElroy's original "Dot Stabilizer".

With advice from another bug user, I undertook a slight redesign of McElroy's original device to eliminate the necessity for replacing the vibrating dot contact assembly. This allows the device to be easily installed and removed quickly with simple tools. I also came up with a further variation on McElroy's design that can be used on even the "Flat Pendulum" bugs such as the Vibroplex Lightning Bug, Military J-36, Zephyr and Champion models as well as various copies of them.

I immediately copyrighted my own design and I currently hold the copyright (C) for this design worldwide, all rights reserved. Anyone wishing to manufacture these commercially or even for sale to clubs, etc MUST contact me first and obtain written permission to do so. I have the right to refuse to allow this and if this copyright is violated, I will pursue legal action.

I currently make "Dot Stabilizers" for the Vibroplex, Speed-X and McElroy keys having the round pendulum and bugs with the flat pendulum, such as the Vibroplex Lightning Bug, Zephyr, Champion and WW2 military J-36 bugs (including the Lionel models) which are based on the Lightning Bug design.

I can also manufacture them for other bugs such as the European made (metric sizes) bugs, etc. as long as you can supply me with the diameter (round) or thickness (flat) of the pendulum and a sharply focused digital photo of the actual bug you want it for. (I only need photos and pendulum dimensions for bugs other than the McElroy and Vibroplex models.) They can be made out of either aluminum or brass though aluminum is the preferred material as it is far less expensive.

I did quit making them for the Japanese "coffin" bugs though as the mechanism is located inside the "coffin" and with the close spacing of the mechanical parts and contacts, it is VERY difficult (sometimes impossible) to mount and adjust a Dot Stabilizer on one of those things. There is too much chance of damaging something so please don't ask me to make one for a "coffin" bug.

Now for something new. In early April 2019, I got a 3 dimensional (3D) printer. After getting used to it and printing a myriad of things that other people had designed, (files that were available on the internet for free), I got the idea to try printing a dot stabilizer. Now, this wasn't as easy as I thought it was going to be as I had no 3D model of the metal ones I've been making for years now. I had to obtain and learn a 3D CAD program (I chose Autodesk's Fusion 360). This turned out to be a pretty daunting task but I finally found someone to help me get started and I was able to draw out the various versions of the Dot Stabilizer to very exacting dimensions to include the necessary holes, etc. A few test prints and tweaks and I now have them for the McElroy bugs and both round and flat pendulum Vibroplex bugs. The flat pendulum ones include the military J-36 as well. I put one on my 1963 Vibroplex "Original" (the test material I was using was green in color) and have been running it ever since. I also sent one to Don, WB6BEE for him to try on his McElroy bugs (he has quite a collection of them). They are all working fine. They do distort a little in the printing process and this is pretty much unavoidable due to the materials used and the temperatures they are printed at but unless they are examined real closely, this is usually not noticeable. It does NOT affect the operation of the stabilizer in the least. The set screw holes still have to be tapped and the "snubber" hook still needs to be made from piano wire, but the use of the plastic printing material has allowed me to make them a bit cheaper Because of the shape of the wire hook I cannot send them overseas without boxing them up and that puts a prohibitive shipping cost on them so they are no longer available at all. Due to shortages and discontinuations by the manuafacturers, the "Tough PLA" I used has now changed enough in formula that it's not as strong so I have discontinued making the plastic stabilizers. Too many people have complained that they stripped out the set screw holes.

In the photo below, I show examples of all three types but these are now for reference only as they are no longer available. The left one is for the Vibroplex round pendulum ones, Center is for the Vibroplex flat pendulum and the right one is for the larger round pendulum of the McElroy bugs after refining the sizes slightly for better fit.


3D printed Dot Stabilizer bodies.



3D printed Dot Stabilizer (in black) on a McElroy key belonging to
Don, WB6BEE (photo courtesy WB6BEE).


Installation and ordering info for the standard models:

They mount to the arm with a socket head set screw and the proper Allen wrench is included along with a printed set of instructions explaining installation and proper adjustment. Also, they are made entirely by hand so there may be slight differences between each one (this won't affect the operation at all).

The prices are $28.50 post paid for the aluminum and $38.50 for the brass ones to domestic USA customers. I am, however almost out of brass stock and brass prices have gone up enough that when my brass is depleted, only aluminum ones will be available.

Due to large shipping cost increases and the extra, complicated Customs forms I need to fill out for export I can no longer ship these internationally (unfortunately that may include Canada).

Please email me W0EB. before you order to check availability.

If you decide to order one or more, I will need the make/model of the bug(s) you want stabilizers for and whether they are "left" or "right" handed (the bug, not you). Also, be sure to include your correct mailing address as well. Payment method(s) will be agreed upon and payment received prior to shipping.


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Some additional images and information provided by a satisfied customer, Fred Schebor, K8NGW after he installed a Dot Stabilizer I made for his left handed Vibroplex Presentation. The following images are Copyright(C) Fred Schebor, K8NGW and are used here by permission.


Left Hand Dot Stabilizer mounted on K8NGW's late model Vibroplex "Gold Base" Original

Since I did not have a photo of a left handed bug with a left handed Dot Stabilizer properly mounted on it to use in the instruction sheet I provide with every dot stabilizer I make, Fred, K8NGW sent me pictures of the one he installed on his Vibroplex Original (Gold Bug) Presentation model. He also gave me permission to use the photo(s) as I needed and gave me a copyright release to do so.

Fred also hooked up a scope and ran before and after tests of the keying waveform using his bug. The first scope screen capture shows the contact bounce that causes the "Scratchy Dots" and the second trace shows the alleviation of the bounce that all but completely eliminates the "Scratchies". Many thanks to Fred for providing these pictures and for his kind permission to use them as I needed.


K8NGW Oscilloscope trace showing a "Scratchy Dot" before installation of the Dot Stabilizer.

And, finally, the last picture shows the effect of an installed Dot Stabilizer on the keyed dot, virtually eliminating the nasty bounce that caused the "Scratchy" dot. I hope these photos and the accompanying explanation helps illustrate the cause and one effective cure for a bug's nemesis, the "Scratchy Dot Syndrome".


K8NGW Oscilloscope trace of a keyed dot after installation and proper adjustment of the Dot Stabilizer.



Jim Sheldon - W0EB


For further information or to order one or more, contact Jim, W0EB.

Page copyright (c) 2019, 2020, 2021, 2022 W0EB, Images copyright (C) 2019, 2020,2021,2022 W0EB and K8NGW (used with permission).

Vibroplex, McElroy, Johnson SpeedX, Lightning Bug, Champion, Hi Mound, etc. are trademarks of their respective companies.



Page last updated by W0EB - 10/11/2022 @ 13:00 UTC