Tube Challenge!! (3)

[Doug Tymofichuk]

On Mon, 29 Nov 1999 18:20:48 -0500 (EST) 
media at mail1.nai.net wrote:

> >I would guess that this is changing the duty cycle of
> >whatever waveform that is sent to the input of the unit.
> 
> Huh??
I will try and be a little more clear with this. But bear 
in mind that I am just guessing, I do not know for sure.

The 6BQ7 tube stage that performs the PWM is probably a 
type of monostable multivibrator. When the input waveform 
is applied to it, it causes it to trigger once per cycle, 
in affect it becomes a second oscillator sync'ed to the 
input signal. Adjusting the time constant for this second 
oscillator to a much smaller value than the input waveform 
time constant will result in a lower duty cycle (narrow 
positive pulses rather than equal negative and positive 
pulses).

Hmm, that doesn't seem abundantly clear even to me, after 
writing it. Hope it helps!
----------------------
Doug Tymofichuk
dougt at cancerboard.ab.ca