[AMPS] Heathkit SB-1000

[Tom Rauch (W8JI)]

I got in a rush to reply, and started doing an AC analysis of dc tube currents.

Tom Rauch (W8JI) wrote:

> > >Cathode saturation current of a 3-500Z begins at approximately six
> > >amperes, and at 500 mA of meter indicated anode current, PEAK cathode
> > >current (which includes grid current)is only about 2 amperes. There is a
> > >3 to one safety margin.

That part was OK, but tonight's post was a mess. 

I said:
> Peak anode current is not "three times the indicated current" in a class
> AB PA.
> With a perfect 180 degree sine shaped waveform, peak current is 2.828
> times average current. With 360 degree conduction angle and a sine wave,
> peak current is 1.414 times average current. The conduction angle is
> about 215 degrees (class AB) at 500 mA effective current, so peak
> current is
> (.6/1 * 1.414) less than 2.36 times indicated anode current. 500mA *
> 2.36 is 1.180
> amperes.

Scratch all that. Peak instantaneous current actually ranges from two to about
three times the indicated meter current, depending on conduction angle and wave shape.
AB is a wide class of operation (from just over 180 to just under 360 degrees).

The peak instantaneous plate current in the case of the SB-1000 is actually
about 1.4 amperes at 500 mA, so Rich wasn't far off in his estimate. He is incorrect
about his saturation theory. I'm going back to bed.

Flame away Rich.

73 Tom


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