Regarding the 3/2 law, Rich asked?:
"In your opinion, what does Eimac say, Colin"
In responding to your same request in December of 1999, I said:
"The 3/2 power law simply states that if you change all of the
interelectrode
voltages applied to a power grid tube by a factor of 2, that the current
will change by a factor of 2.8.
In the G2DAF amplifier, the grid voltage and screen voltage vary in relation
to the drive, while the plate voltage remain constant. One unique feature
of the G2DAF circuit is that the ratio of grid to screen voltage varies
depending upon the drive as a result of the inefficiency of the half wave
doubler circuit. The more screen current that is drawn, the lower the
relative voltage applied to the screen.
The 3/2 power law is a simple conversion process for changing all of the
voltages on a screen grid power tube. It neither proves nor disproves the
theory of the G2DAF design.
However, if you put a 2 mfd capacitor on the screen, overdrive the grid, use
a 4CX250 tube and yell into the mike as Norm did, then you can splatter."
I also quoted directly from Eimac's "Care and Feeding" book in a follow up
messagel:
"the screen voltage is not critical for most applications and the value used
has been chosen as a convenient value consistent with low driving power and
reasonable screen dissipation. If lower values of screen voltages are used,
more driving voltage will be required on the grid to obtain the same plate
current. ... The value of screen voltage can be chosen to suit available
power supplies or amplifier conditions."
Upon reflection, my opinion of the 3/2 law remains the same today.
Colin, K7FM
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