Tube Challenge!! (3)

Doug Tymofichuk dougt at
Tue Nov 30 15:58:54 CET 1999

On Mon, 29 Nov 1999 18:20:48 -0500 (EST) 
media at 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 

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

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