My comment:

There is a third method of bias: contact bias, which is used in such first audio tubes as 6AV6,

which gives up to about -2 volts, with no signal rectification and no cathode bias resistor.

Also, if you use any reasonable analog meter with a rating of 20,000 ohm/volt or better, on say,

its 25 volt range, you are not going to seriously affect the voltage reading across ~250 ohms

resistance.

-Hue Miller