[Amps] sb-220 non uniform grid current ??

[Dan Sawyer]

All,

I have an sb-220 with non-uniform grid current. With low to medium drive 
grid current is linear (or apparently close to it) with plate current 
(minus about 100 ma base) and output power. However if input drive 
exceeds the medium level of 25 to 30 watts grid current starts to hockey 
stick "high". It is not a digital switch; but a very steep response.

The components in the bias and grid meter side of the circuit have been 
checked in circuit. The grid bias coil has been replaced with an 1/8 
watt 33 Ohm resister.

Thanks,
Dan