Hi there, hoping you can point me in the right direction, here's the problem and what I have done so far: Problem: V9 and V10 show no current passing when I connect bias probes to all four tubes, V8 shows 44mA and V11 shows 52mA. All four tubes light up and get hot. Original tubes were SOVTEK 5881/6L6WGC but 1 broke in transit so tube depot provided new matched set of JJ 6L6GCs as replacement tubes. The amp passes signal OK and output is not distorted as seen on a scope. 1. Swapped bias probe and tube over and the problem stays with the sockets. V9 & V10 always have no current. 2. Checked the pentode/triode switch and its set to pentode. Tested switch with amp off and switch appears to be operating normally. 3. Checked the fuse for V9/V10 and this is OK. 4. Voltages to earth on all four sockets seem almost the same 3 is 478v, 4 is 475.5v, 5 -47.6v 8 is 0.011. Heaters to earth 2&7 are approx. 3.5v ac 5. All screen resistors are 470ohm 5w and good. 6. Checked the low power switch: set to high and tests OK. 7. R272 looks a bit cooked but measures correct at 100K 8. AMP had an extra 5K6 resistor on pin 5 of V11 (removed since schematic error) Did I miss something obvious? Don't want to remove circuit board unless I have to but running out of obvious things to try.