power tube quad confusion

[Randall]

I have a cathode biased Dr Z Remedy head in with two dead 6V6s and no fuse. The other two 6V6s test good, so I was going to offer to replace only the two dead ones, figuring I could match a new one with a used one in each side and the draw should be pretty even from side to side. First, please correct me if this is not a good way to go to try to save a broke musician some money (I like their band).

Second as I look at this, I find the two on the left share the same blue OT wire, and the two one the right share the same brown OT wire. But, there are two cathode resistors, and V1 and V3 share one cathode resistor, and V2 and V4 share the other. So, each resistor serves a tube with a blue OT connection and one with a brown OT connection. This is confusing to me. The grid wires follow OT wiring with the two on the left paired, and the two one the right paired. The Hi/Low power switch shuts off V2 and V4.

So, what is up with this?

[eschertron]

Seems like a fine idea to me. If there were only two power tubes, they would share one cathode resistor for alternate sides of the push-pull. Add two more output tubes and add another cathode resistor (as Dr Z seems to have done). This allows the user to REMOVE two of a quad of power tubes and not have to worry about rebiasing. Only matching output impedance.

[Dave H]

I find the two on the left share the same blue OT wire, and the two one the right share the same brown OT wire. But, there are two cathode resistors, and V1 and V3 share one cathode resistor, and V2 and V4 share the other. So, each resistor serves a tube with a blue OT connection and one with a brown OT connection. This is confusing to me. The grid wires follow OT wiring with the two on the left paired, and the two one the right paired.

My 4 x 6V6 amp is wired like that.
If you have two matched pairs but not a matched quad put one matched pair on the V1,V3 cathode resistor and the other matched pair on the V2,V4 cathode resistor. You don't want to have non matched tubes sharing a cathode resistor.
My amp will also run on 2 x EL34 in V1,V4 (or V2,V3) sockets.

[Randall]

AH, it makes sense to me now, since you put it like that. Thank you.