>
>Carl wrote:
>
>>Ian, what would be the impedence of a vacuum tube series regulator?
>
>If it's in some kind of feedback circuit the impedance could be very
>low. The same is true of a shunt regulator, eg something using an 807 or
>a similar smallish transmitting tube, if you use something like an op-
>amp or a 723 to generate the loop gain in the feedback circuit. (You
>also need to mess with the op-amp frequency compensation to give a
>stable feedback loop.)
>
>>And
>>what effect if any would it have at a Es of 1KV or more?
>>While a 4CX250 would require a regulation of 1 volt or less for IMD
>>reasons would that hold true with large tetrodes?
>>
>>Perhaps a tutorial on exactly what is involved in determining the screen
>>regulator impedence is in order. I admit to being somewhat confused by
>>all the claimed numbers of various methods.
>
>It's hard to say how much regulation is needed, except by doing tests.
>The IMD data exist for 4CX250s, thanks largely to GW4FRX who showed that
>tight screen voltage regulation usding an active feedback regulator
>makes a notable difference to real-world IMD (see charts on my web
>site).
>
>As far as I know, no similar data exist for other types of tube - it's
>all done by extrapolation.
>
>However, there is another big advantage in using an active feedback
>regulator: it allows very effective circuit protection to be added
>without any penalty on the voltage regulation. Even if you believe that
>zeners give a low-enough supply impedance, it's much harder to still
>believe it after adding a relay or some other circuit in series to sense
>excessive screen current.
With a shunt zener-string regulator, one does not sense excessive screen
current. The value of the series resistor from the screen/zener-string
to the anode supply is selected so as to limit screen current to a safe
value at all times. In other words, screen protection is automatic with
a zener shunt screen regulator. .
>
- later, Ian.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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