Here's the SV20 schematics from Marshall !

[Joesatch]

1.2k input grid ?

 

[Matec1]

Pretty strong statement, what is wrong with the font? Or, explain exactly what you find wrong.

It is an error in the design of the transformer. The secondaries of the original transformer are separate. One for each voltage. There they appear as if they were one. This is a disaster.