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audio modulated VTTC

Original poster: "Herwig Roscher by way of Terry Fritz <twftesla-at-qwest-dot-net>" <herwig.roscher-at-gmx.de>

Hi list,

I've built an audio modulated VTTC and find the quality of the 
radiated AF not to be overwhelming at all. Plasma tweeters are 
kind of VTTC and are reported to generate high quality AF - at least 
at high modulation frequencies.

Searching the web, I've found, that most VTTCs are Armstrong 
oscillators, operated in "C-mode" (no true C-mode, which requires 
a constant grid bias). One of the advantages, claimed for this type 
of oscillator is, that it is selfstarting and selfregulating.

Plasma tweeters nearly almost are Huth-Kühn (in this part of the 
world)-oscillators (feedback by increased capacity between plate 
and control grid). This type of oscillator seems to have start 
problems and it is necessary to touch the terminal with a well 
insulated screwdriver to stimulate the oscillations.

Because of simplicity and low distortions I would like to use the 
plasma tweeter type of oscillator for my VTTC. But I am not 
prepared to accept the start problems, as they are a huge menace 
for the toob.

What are the reasons for the a.m. problems and is it possible to 
overcome them? Are there other types of power oscillators which 
combine easy selfstart and good modulation quality and could be 
used for VTTCs?



Greed is the root of all evil!