G0MJW wrote:
>
>
>The zener diode can be replaced with a series of c. 7, 1A forward-biased
>diodes. Such an arrangement is much more rugged than a zener.
>
>And also poor regulation - Does it really matter ? If you are doing that you
>might as well just use a resistor as the bias is only a few volts and it
>will probably still be cleaner than the driver. I suggest you use a low
>power zener and a transistor, or a programmable zener like the TL431 and a
>pass transistor. G3SEK might comment.
The TL431 circuit is at:
http://www.ifwtech.demon.co.uk\g3sek\boards\triode\triode-3.htm
It's fully adjustable and certainly cheaper than a large zener.
I don't really know how the IMD varies with cathode bias regulation.
Mostly, I use the precision regulator in order to reduce any additional
bias voltage changes caused by the protected grid current metering
circuit (on the same web page).
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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