Different Plate voltages on EL84's

[ajkimba]

Was wondering if getting different plate voltages on the power tubes could be a sign of mismatched power tubes.

I don't have a tube tester and a bunch of used old El84's with no way of matching and was wondering if I could just try to match them up by checking the plate voltage...? And listening to the tone.

[lastwinj]

if you have the cathodes of each power tube individually biased, you could match them up by matching the voltage on the cathodes. or if you have a champ set up for el84, could check them that way.

[brownnote]

Sometimes I think that's the best way to approach tone...just experiment until you have something that sounds good, then check the specs on it to understand what's going on.

[markh]

Static plate voltage is partially dependant on the OT and partially on the tube.

Even well-made output transformers differ in secondary resistance from side to side by 5% or more.

The individual plate curve of the tube under test will have a larger effect on the plate voltage.

Note that there is some interaction between the two tubes in a shared-cathode-resistor environment like the 18watt.

A better way to do a first-order matching would be to setup a test jig with, e.g., 270 ohm cathode resistor, an 8k2 plate resistor and 300 or so volts B+. You could at least roughly sort/match them by plate voltage with this test.

--mark h