[Hallicrafters] HA-1 keyer

[Roy Morgan]

At 10:51 AM 11/23/2005, k2wh at optonline.net wrote:
>Could someone please explain to me how a regulator tube goes into 
>"Oscillation"?  I have never heard of such a thing.  Is this possible?

Yes, very possible. In fact a resistor, a neon bulb or VR tube, and a 
capacitor make a fine "relaxation oscillator".  Here's how it works.

The voltage regulator often has a small capacitor in parallel with it, to 
reduce noise and to improve circuit performance at higher frequencies.  If 
the circuit feeding the VR tube has high resistance, and the load on the 
thing causes the tube to extinguish, then the capacitor will more or less 
slowly charge up to the point where the tube fires again.  This can then 
pull the capacitor voltage down below the ignition point and the tube shuts 
off again.  The result is that the thing charges up, fires, the tube shuts 
off, and it cycles on like that.


Try this if you have the parts: put a 0.1 or 0.01 uF cap in parallel with 
an NE-2 or NE-55 neon lamp, and feed it with a 100 K resistor from about 
100 volts DC or more.. see what happens.  Simple code practice oscillators 
have been made with this idea.

If you make a ring of such circuits, the lamps will light and extinguish in 
sequence making it appear that the light is travelling in a circle around 
the ring.  Two rings of 2 or three lamps each make an apparent random display.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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