G Amp schematic Joe Piazza. In the event of a tube short failure or simply a transient overload condition the diode will conduct once the current in the 22ohm screen resistor reaches 30mA and beyond, preventing further burning of the PCBA. Unsourced material may be challenged and removed. Nov 27, Vintage ampeg schematics. And what does "work better" even Vintage ampeg schematics Their phone number is Log in or Sign up.