> For small tetrodes with less than roughly 800v screens, a zener-string
>
> shunt regulator works best. For larger tetrodes, a 723-based positive
>
> floating series pass regulator has advantages. You can find both types
> at:
> http://www.vcnet.com/measures
> Rich---
>
> R. L. Measures, 805-386-3734, AG6K
There is some data on G3SEK's web page, by GW4FRX, on the IMD
performance of 4CX350s (which need about 400 V) using:1) A well
stabilised screen supply.
2) The screen stabilised supply with a resistor 150 Ohm added to worsten
regulation.
3) A zener diode chain.
The results are the zener chain gives the worst IMD performance, the
stabilised supply the best, and the stabilised+resistor in the middle.
It not my data, but does rather indicate that zeners are *not* the best
for small tetrodes.
Check out if you are interested:
http://www.ifwtech.demon.co.uk/g3sek/
There was also an article in VHF communications about 6 months ago on
the noise generated by zener diodes (which are always less than about 6
V, contry to popular usage of the term), avalance diodes (which are
always > 6 V, and frequently called 'zener' diodes), and LEDs as voltage
regulators. Interestingly, the noise source impedance is much lower than
the dynamic resistance, which means that you cant do much to reduce the
noise by shunting the diodes with capacitors, as the noise impedance is
so low. LED's on the other hand generate little noise.
--
Dave Kirkby G8WRB
Department of Medical Physics,
University College London,
11-20 Capper Street,
London,
WC1E 6JA.
Tel: 0171 209 6406 (International +44 171 209 6406)
Fax: 0171 209 6269 (International +44 171 209 6269)
--
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