As for the 300B, I do not know. Based on specs, setting filament to 5 volts, and the other settings to that of a 2A3 should be close to correct. Those settings are not exact, but it would allow for an approximate balancing of two tubes as good as any emission tester would allow.
Specs for the 300B:
http://www.westernelectric.com/spec_sheets/300B.pdf
specs for 300B
The 310A is also in the list among many others.
http://www.westernelectric.com/spec_sheets/we_spec_sheets.htm
List of archived WE specs.
: Did somebody know how to set a jackson 648a for 300b and 310a tubes
: Thanks
: Pascal