Biasing Mixed Power Amp operation

[lowell]

Hey all,
I'm playing w/ an amp w/ 2 6v6 cathode bias and 2 6L6 fixed bias. Obviously I have 1 of each on each side of the p/p OT. Any tips on biasing these? I'm thinking that current will be split evenly b/t them. Is that correct? So if I want to bias my 6V6 at 90% dissipation (cathode bias) and that is about 30ma at 450v, then when I put the 6L6 in their sockets and measure bias should I bias one side of the OT at 60ma?

[defaced]

When I have done mixed pairs (KT-88/6CA7/6L6, various mixes), they have been fixed bias with a bias supply for each pair, and each pair has pulled different amounts of current. Because the tubes are in parallel, and they have different V-I characteristics (think of them as two resistors of different values in parallel) they will pull difference amounts of current. What they will see is the same B+ voltage.

My bias procedure has been to bias one pair, then add the second pair and bias them, then re-check the first pair.

[lowell]

Ok so I'd bias the 6V6 to 30ma, then put the 6L6 in and any additional current ADDED to the 30ma, I can be sure is being drawn by the 6L6?

[lowell]

perhaps transformer shunt method doesn't work here. I may need to put the meter in series w/ each tube?

[defaced]

From the hip here... I think you had it right in your first reply. If you know the current for one (across cathode resistor), and you know the current for the sum of the tubes (transformer shunt), then you can figure out the current for the second pair of tubes. But if push comes to shove, series current readings (or across a low value resistor for the 6L6s) are valid.