Re: Screen supply sources



shoppa@xxxxxxxxxxxxxxxxx wrote:

John Byrns wrote:
In article <HVbdg.98076$dW3.32460@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
admin-n-att--tubezone-dott-net wrote:

shoppa@xxxxxxxxxxxxxxxxx wrote:

It looks like I'll be using it as a shunt. With the 807 spec ***
telling me typical AB1 PP operation has screen currents of 5mA to 20mA,
it looks like 30 mA or so through the shunt regulator will be about
right, and that seems to be their sweet spot. This will also allow the
VR chain to serve as a bleeder before plate current kicks in.

Sounds like a good plan.

I believe that the "screen currents of 5mA to 20mA" mentioned in the spec
*** is the DC value

I think you are right. Although I would be surprised if the
instantaneous AC currents ever got to twice that.

That depends on the loadline line & the program level. In an ideal world the
loadline would run nicely up into the knee of the pentode (or UL) curve. But a
complex load such a lautsprecher will go Hi-Z on it's resonant frequencies. As
the plate voltage bottoms out on those peaks, the screen current will go very
high, indeed. The resulting screen currents are sometimes shown on the published
plate curves.

That is why I pick a loadline of lower Z than what would give max power. That
lower Z load line also decreases 3rd H distortion, something the PP connexion
does nothing for at all.

Cheers, John Stewart

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