I purchased my Amplidan key on Ebay as many others have done, about three years ago, at the time they were not considered anything really special and although they were obviously a quality key the average price was about $120
this has now doubled and tripled up to the present time, and now they seem to have reached that stage where
rare items often acquire mystical qualities, It is a very nice key and does have a very nice action which can be described as almost frictionless, machine like, yet possessing a lively feel to it, almost a bounce when set with a light tension, but this is not unique I know at least four other keys that are very similar in performance and in my estimation equally as good, though this is hotly disputed by some, The reason this key performs as it does is not magic, I have now made over one hundred and twenty handmade straight Morse Keys in every possible mechanical combination its possible to imagine, including two Amplidan designs, I've also handled and used hundreds of manufactured keys commercial and military, and I like to think I now have a good idea as what makes a key action feel the way it does, it's a deep subject but in this case I shall direct my ideas to the Amplidan 50713, as there are other Amplidans around old and new including a very unusual single adjuster that I've only seen one example, but the 50713 is what most people consider as being the famous "Amp" the basic action of the Amp is what I call a twin spring system, where one hard flat spring is opposing a softer coiled spring which is normally adjusted in length to provide a variable tension, I would hate to go into the mechanics of this, all I can say is that it seems to produce a very linear adjustment spread out over quite a few turns of the tension adjuster, usually the flat spring is placed in front of the coil spring which is closer to the pivot point, the main difficulty if you want to make a key like this is obtaining suitable springs of the right quality and spring tension to balance the weight of the arm, the Amp is considered to be what is known as a long lever key, the theory is a longer handle produces more control as a large movement of the handle only produces a small movement in the contacts, also the added weight of the handle adds a sort of kinetic energy to the key when its operating at speed, this can produce a very hard action as when the contacts close there can be quite a bit of energy that has to be dissipated, the Amp gets round this by having a sprung contact in the nose of the key, the handle is cut short and a thin brass strip attached which absorbs this energy and gives the key its lively feel, the Amp also has what I call pin pivot bearings, where the axle of the pivot is coned and sits in the two adjusters each side, the adjustment of these pivot bearings are really critical to the operation of the key, to tight and they bind, to loose and although you have a very low friction pivot the arm will swing from side to side, so its a compromise between friction and acceptable sideways movement, I personally don't like this sort of pivot and in my Mk2 version of a handmade Amp I used ball races which are incredibly low friction and at the same time provide virtually no sideways movement if fitted correctly, also in the Amp these adjusters just sit in tensioned slots to hold the adjusters in place, I personally think that this is not an ideal way of pivoting a key but who am I to criticize the Amps designers :) in this case it seems to work very well as the machining is excellent quality,
What is not generally known is the electrical qualities of the key, with its lid on it is completely isolated, both the handle and the adjusters are isolated from the terminals, the Amp achieves this by having insulators on the sprung contact strip to isolate it from the handle and the gap adjuster has a ceramic plug in the end of the threaded part that pushes onto another sprung contact that goes to a terminal, some would argue that this piece of ceramic somehow gives the key a special feel, well in the course of making a couple of Amp copies I've tried my original Amp with and without this piece of ceramic and I didn't notice any appreciable change in performance, Getting back to the design the Amp sits on a Very long and heavy steel plate base, there is no doubt that a heavy base certainly adds to the performance of a key but what also Must be included on a heavy base is some shock absorbing material under it, on the Amp this is a green felt material, this is an integral part of the key and must never be removed or I can assure you its performance will suffer. and then there is the knob shaped like a babies comforter, it certainly gives a unique look to the key though I can't say it improves the keys performance, what can and does alter it is a small piece of hex bar that sits under the knob, this adds about 1 ounce to the arm weight, I have removed it for tests and it does change the feel of the action slightly, whether this is intended or just for cosmetic purposes I don't know, and finally there is the spring loaded gap adjuster, it is an interesting mechanism made so the contact gap can be adjusted with one hand without any locking required, it is quite simple, a brass tube has a slot cut into it so that it straddles the contact post, inside is a large spring which pushes it upwards, a cap is fitted over this and is attached to threaded contact screw, this is held in the set position by the spring pressure from the tube under it, and both the tension adjuster and the contact gap adjuster have very thin greased paxolin washers under them to give a very smooth feel to the adjustments.
All this adds up to a quality key with some quite unique features, however having said that I think it could be simplified quite considerably for amateur used, the insulated contacts are really not required with today's solid state switching which would simplify handmade construction considerably, and I'm pretty sure from experiments I've made that the flat spring could be removed and a harder coil spring fitted closer in to the pivot point which in my opinion produces a better feel to the action than the dual spring system, the pin pivots could also be replaced with ball races, I'm sure this would not affect the quality of the action maybe even enhance it, and yet maintain the sleek lines and looks of the Amp, I may make another Handmade Amp the Mk3 with slight differences or even a half scale version would be fun :)

   Ron Ayling G3YUH Margate 20/2/08