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RE: Why is Square / Rectangular Wave Deal of the Day?

Posted by dave slagle (M) on December 7, 2016 at 19:09:26

In Reply to: RE: Why is Square / Rectangular Wave Deal of the Day? posted by Triode_Kingdom on December 7, 2016 at 15:04:27:

How does the square wave heating affect the bias? With DC, you can shift the bias by the filament voltage depending which end of the filament you reference to ground. With AC, you simply take 1/2 the filament voltage and add it to the bias. I would guess you would do the same with the HFac but then making it a square wave makes me scratch my head a bit.

The reason I bring this up is I have a µTracer that operates off of a 20V laptop supply. In order to do the filaments it uses PWM off the 20V supply and alters the duty cycle to give the desired heating. What is interesting about this is that it samples each data point for 1ms and times it to sample when the PWM is in an off cycle. This means that the tube is actually traced with 0v on the filament and no filament gradient whatsoever which is very different that the gradient given from DC or AC sine heating. Moving this to HF square waves makes me see the bias voltage abruptly shifting the full filament voltage and wondering if that is a good thing.

thoughts?

dave

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