You are measuring voltage difference from one side of each plate resistor to the other side (no ground reference) with the amp ON; no standby--like you were going to play it, but with no signal (turn the volume's down when you do this)
You will get a measure that is the voltage drop across the resistor It will be less than 1V at idle most likely (or...well...).
You are then looking for current - that is, your idle current draw.
Ohms law tells us, Current = Voltage / Resistance.
Once you know the voltage drop, you divide the voltage you get by 10 (since your plate resistors are 10R).
Then you get a current, measured in Amps (it will be a decimal since you are looking for miliamps.
Then you compare this to the next 3 tubes, doing the same.
Ah, yes, tubedepot...a matched quad will be...well, hopefully within 10% here. The high voltages seem to make "matched pairs" significantly less "matched" than originally stated, from most sources.
Once you see how differently they all bias, you can try and swap them around and pair them up differently.
Put the two that draw the most current as a pair (outer or inner pair) and the two that draw the least current as the other pair (outer or inner pair).
Try to balance the overall current draw between the two sides as well, so if you have 4 tubes, each draws a different idle current, 1 being the least 4 being the highest, they are ordered something like:
4 1 2 3
4 and 3 are one pair, 1 and 2 are another pair, and lowest and highest are on the same side to try and equal out the total current draw on "one side" as compared to the "other side" of the PT that has 2 & 3.
Fun?
If you use this calculator:
http://www.james-gang.org/jca/Bias.php
Using 540 as the plate voltage, 6L6GC as the tube type...60% at idle is 33ma! IMO this is absolute MAX in this case!!! IMO, off the top of my head, 22-26ma would be much much much better tonally and for lifespan...you'll only have so much room to play with if your tubes all mismatch, but if even one tube is drawing 34 ma+ at idle, I'd definitely change the bias resistor.
You will get a measure that is the voltage drop across the resistor It will be less than 1V at idle most likely (or...well...).
You are then looking for current - that is, your idle current draw.
Ohms law tells us, Current = Voltage / Resistance.
Once you know the voltage drop, you divide the voltage you get by 10 (since your plate resistors are 10R).
Then you get a current, measured in Amps (it will be a decimal since you are looking for miliamps.
Then you compare this to the next 3 tubes, doing the same.
Ah, yes, tubedepot...a matched quad will be...well, hopefully within 10% here. The high voltages seem to make "matched pairs" significantly less "matched" than originally stated, from most sources.
Once you see how differently they all bias, you can try and swap them around and pair them up differently.
Put the two that draw the most current as a pair (outer or inner pair) and the two that draw the least current as the other pair (outer or inner pair).
Try to balance the overall current draw between the two sides as well, so if you have 4 tubes, each draws a different idle current, 1 being the least 4 being the highest, they are ordered something like:
4 1 2 3
4 and 3 are one pair, 1 and 2 are another pair, and lowest and highest are on the same side to try and equal out the total current draw on "one side" as compared to the "other side" of the PT that has 2 & 3.
Fun?
If you use this calculator:
http://www.james-gang.org/jca/Bias.php
Using 540 as the plate voltage, 6L6GC as the tube type...60% at idle is 33ma! IMO this is absolute MAX in this case!!! IMO, off the top of my head, 22-26ma would be much much much better tonally and for lifespan...you'll only have so much room to play with if your tubes all mismatch, but if even one tube is drawing 34 ma+ at idle, I'd definitely change the bias resistor.