Saturday, October 19, 2013

Vintage Radio Construction Etc

 Sunday, 27th August 2017

Semi Automatic "Bug" Morse Key
Feeling like a change from ship models, a few days ago, I decided to try and build a semi-automatic bug key.      This type of  morse key was first developed in the United States.    Conventional morse keys move up and down, and both dots and dashes have to be made manually.     When I first went into passenger liners as a junior radio officer in 1965, I found it very hard going sending large numbers of messages, often containing hundreds of words.     My wrist was quickly in danger of seizing up, so I obtained a cheap Japanese bug key in Cape Town.     The bug key works horizontally, and the side of the palm can be rested on the desk.   Pushing the paddle to the right with the thumb, produces a string of dots by vibrating a piece of weighted steel spring with electrical contacts fitted.     Pushing it to the left with the forefinger, the dashes have to be made individually.    I found this a great help, and was soon able to send for considerable  lengths of time without getting tired.    In the next twelve years, I got through two Japanese bug keys, the first being accidentally dropped by the third radio officer when it was only a few weeks old.   That broke the paddle arm off, and I had to effect a temporary repair until I could replace it again in Cape Town.    Despite being quite cheap, I had no complaints about the Japanese keys, they were really good.   But I had heard that the American Vibroplex keys were the best of the best.    Eventually, I was able to purchase on in Houston, Texas, for about £50.     I used that one regularly from 1977 until leaving the sea in late 1992, and still have it today.   The key illustrated is purely my own design based on trial and error, and it took almost a week to get it working correctly.    I have compared it with my Vibroplex, and although I am a bit "rusty" at morse after 25 years, can still produce perfectly readable code, and cannot tell any difference in handling between mine and the Vibroplex,
I incorporated small ball races for the top and bottom bearings that gave a very smooth action.    The spring steel is a piece of a junior hacksaw blade with the teeth ground off.     The vertical pillars are all old rifle shells cut off to the correct length, and bolted to the acrylic base via holes drilled through ends.   The dent caused by the firing pins was a great guide for the drill.    The open tops were fitted with home-made caps made from brass, with a fancy brass bolt in the top for purely aesthetic reasons.     Solving the spring problem was beyond me, as I could nor find any springs small enough, or of the correct strength.    I got round this by using powerful neodymium magnets instead of springs, and they work really smoothly.    The tension can be easily adjusted by moving the magnets further apart, or closer together.     Neither could I get the dot contacts correct, so I used a small magnetic reed switch.   It is actuated by a magnet fixed the vibrating arm.    The speed of the dots can be adjusted by moving the brass weight along the vibrating arm.    The closer it is moved to the front of the key, the faster the dots.     Most of the construction is in brass.    The base and paddle are acrylic sheet and the finger knob is a small "button knob" normaly used for glass cabinets.   Four imnages of the key are shown below.    I am now thinking about fitting a self-containedvalve oscillator and small loudspeaker to it.   I think there is just about enough room to accommodate all the components, speaker and batteries.

Friday, 27th January, 2017
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Building a 3-Valve TRF Receiver (£2.99)

Building a One Valve Radio Receiver (EF91 Valve) (£1.99)

How to Build a One Valve Radio Receiver (EF91 or 1T4 versions) (£1.99)