[Amps] bias problem

[Φραγκιαδάκης Παναγιώτης]

it will be a greate help if you tell me why do i have zero bias
when i drive a linear amplifier at the G1 and when is not drived the bias is normal minus 125 volts there is a pair of 
4-400 in paralel the linear was working ok anode is 2800 dc and G2 is 480 vdc there is a pi input and a pi output
in sort is a clasic desine
eny ideas why is hapening when i put drive power the bias going down ??

regards panos 
SV4JYI