Re: First light with 833 tube coil, then silence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Mddeming@xxxxxxx 

In a message dated 9/24/06 12:47:21 A.M. Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:

Hi David,

I might be missing something, but the schematic looks like the
secondary of T1 is connected to the plate thru the primary of the
TC.  It seems like half of the time, the plate voltage will be
negative and I don't see how that would work.  Doesn't the T1 secondary
need to be rectified and filtered first??

Gerry R


Hi Gerry,

You're not missing anything. The tube does not conduct at all during 
the negative half of the cycle. This is sometimes called "self 
rectification" and results in  50% or less conduction. This means you 
are getting oscillation only half of each power supply cycle and then 
only when the voltage out of the transformer is high enough, 
resulting in somewhat less than 50% oscillation time. A push-pull 
oscillator configuration would give twice the "on-time" but still 
less than 100% as there must be a minimum voltage to initiate and 
sustain oscillation. A rectified power supply would be the only way 
to get constant, uniform output. The circuit shown substitutes 
simplicity for efficiency, which for many folks, is OK. A multi-kW DC 
supply with appropriate pi-filter is not a trivial design problem and 
is a hefty piece of hardware which most people would not want to get 
into, neither is a push-pull oscillator with a matched pair of tubes.

Matt D.

"Vacuum tube circuit design is something that most young engineers 
don't know and most old engineers can't remember" W. F. Alcock