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.
Changing from a passive to an active circuit with an op-amp or a 723
makes a quantum leap to "far better regulation than you'll ever need."
Having made that jump, the question of "how much regulation is *just*
enough?" ceases to be interesting.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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