[Johnson] Viking II Keying Mod - Looking for Info

[Mark V. Johnson]

I have a Viking II that has  what very likely appears to be a factory 
installed keying circuit mod.  There is a small chassis mounted on the 
internal shield  by the crystal board that has a 12AU7 tube and 
 associated circuitry. I am lead to believe that its a keying mod 
designed to delay osc. turn on to minimize chirp??
My Viking II Manual makes no reference to it? Would anyone have a 
schematic or info?
Many thanks

Mark V. johnson VE3DJU/VE3DDI