[Boatanchors] pilot light substitutions

[Dick KF4NS]

I do not have a 51 bulb (somebody changed the socket, orig. was a 50) 
for my Heathkit VTVM but lots of others. Has anyone done substitutions 
for this bulb or any others without changing the type of bulb socket 
and is there a rule of thumb for the type and value of a limiting 
resistor if I use a lower E and I rated bulb?

Kind of hard to calculate without breaking out the tube data for 
min/max filament  I&E on each tube in series and then consider the 
aging of the tubes, then get the full data on the bulbs, etc.

Your advice will be appeciated.

Thanks and 73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!