[Eliot Ness]

Personally I wouldn't bother doing that with a tube as readily available as an 80. You can get a new 80 for $12 or good used for $6:

https://docs.google.com/spreadsheet/ccc?...0foD#gid=4

It won't be a globe but it won't require kludging in diodes and resistors under the chassis either. Keep your eyes open and you'll eventually find a good globe 80 on eBay, a radio meet, an old parts set, or a wanted ad. There is no shortage of globe 80's out there if you're patient.

I'd also measure B+ with a good 80 and then your weak one; often a weak 80 isn't that far off, depending on the parameters of the tube tester used.

If you're still determined you can use two 1N4007's and a wire wound resistor to drop the B+ down to what it measures with a known good 80 in the circuit.