Showing posts with label Tricks And Topics. Show all posts
Showing posts with label Tricks And Topics. Show all posts

Diode Spark Killer for Semiautomatic Key

swing hell yes
lots of swing is a pain to copy
a bit of swing, is a horse of a different color
add a bit of a chirp and some drift
cans on head
pre war receiver
turn down the lights
sit by the glow of the tubes and dial lamps

  © W8ZNX
I'm not sentimental, I'm just as romantic as you are, so I agreed with Mac W8ZNX that "a bit of a chirp and some drift" is not a drawback, it is an attribute, trait of a telegraph radio station, especially the Glowbug one. Just a bit, not too much, and how big this bit should be, I prefer to choose myself.

Well, I used to use a Straight Key, then learned a BUG, and everything was fine until I used a cathode keying of a rock bound oscillator or a differential keying of my Magic Eye MOPA transmitter. When I tried to manipulate the high impedance grid circuit of the TNT oscillator, I got a pretty nasty instability of note, specifically at the dots generated by semi-automatic key (dot contact spring, you know).

Quick patch and further explanation:

germanium diode and early speed-x bug

As I see it, the dot contact spring produce a micro spark, discharging the bypass capacitor sporadically, so that every time the exciter starts to oscillate, it has unpredictable remaining voltage on the tube grid. This effect is negligible on dashes (non bouncing contact), as well as in case of cathode keying (low impedance circuit).
Anyway, additional germanium diode on the BUG contacts solved the problem and I got exactly what I want - "a bit of a chirp and some drift", not too much.

WARNING: Can reduce clicks and improve the signal even if you use a cathode keying or rock bound oscillator.