I see a lot of spaghetti and a lot of stuff not on the original schematic. This is heavily modified!
On the two tubes that went red plate the bias resistor is cooked. The resistors on the two remaining bias resistors are 15ohms. I get the math now using ohms law (I = V / R). So my voltage should be .75 (750mv) with a 15 ohm bias resistor on each tube. If my bias resistor was shared then I would halve this number. Now the really strange stuff:
- all my tubes are missing pin 5 (I think but looking at schematic it must be pin six missing)
- pin 1 is not connected to anything on every tube
- pin 4 had a 30 ohm resistor before going to the transformer on every tube
On the pull down resistor I see a 22 ohm resistor off of pin 5 to 6 (one of these pins is not is use - see above bullet) and them wires are going from pin 6 to the unknown board. It looks like it is connecting to the white and green cap and green resistor that you see on the top picture of the amp (example right side right of the right 6922 tube up front). Then there is a series of three blue resistors. I will have to look at it later tonight to determine if this is where point 21, 22 and 23 is (or 1, 2 and 6). I am assuming if these are on this board then they may have accounted for that.
Looks like my first task will be to replace the two fried resistors. When the amp last went red plate it sounded fine, if that means anything at all. Looking at the two tubes that went red plate (happened about a week apart) the silver at the top of the tube is less than the other two tubes, so I am guessing best case I have just lost some life on them. I do not see any other burnt electronics. Could the tube socket get damaged, because the pin 8 seems lose?
There is a Repair sticker on the bottom for some place in Oregon (503-284-8693). I am calling them later today.