[Amps] A question about grid bias in G3SEK's control board

[Ian White]

>
>Good morning and evening!
>  Here is   grid bias power supply in G3SEK's control board
>:http://www.zmdz.com/bbs/incomefiles/20144/1912574624747.JPG
>  I do not understand how it works. I think it is not  a regulated
power
>supply. If it work, should be modify as red line marked and replace
>NTW5142E
>by TL431(adjustable) or TL431 series a zener(higher volt)
>          Hsu

There is no need for active grid-bias regulation because the circuit is
designed for class AB1 operation. This means that the grid current is
always zero (or very close) so the grid bias supply never has to handle
any significant variation in load current. 

Class AB1 operation condition is strictly enforced by the overdrive
protection circuit. The first small peak of unwanted grid current (100uA
for only a few milliseconds) will produce full ALC output, and a grid
current of about 3mA will trigger a complete shutdown. 

For all of those reasons, the existing zener-stabilized bias supply
meets the necessary requirements. 

 
73 from Ian GM3SEK