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

[Hsu via Amps]

Thanks.
   Most of amplifier only use one transformer, the secondary's Voltage can 
dip about 15- 20%  when full load.
If it did not  regulated,the bias Voltage  will chage. I think the ruglated 
power supply is necessary unless you use anlther small Xformer for G1 power 
supply.
I notice that R105 much more than RV102, so It is regulated power supply, 
but not 100% full regulated power supply.Is that right?
   73!Hsu
  PS, I have noticed some Big tube(4CX10000D) Class AB1 amplifier  with G1 
regulated power supply but can handle reverse G1 current and with reverse 
G1 currend meter.

-----原始邮件----- 
From: Ian White
Sent: Saturday, April 19, 2014 8:50 PM
To: 'Hsu' ; amps at contesting.com
Subject: RE: [Amps] A question about grid bias in G3SEK's control board

>
>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