On to another one. This is the one I mentioned above that has high voltage and has been recapped. I tested before a load and got 299v at R2 and -30v at R9.
First thing I would do: plug in a mic and monitor on your meter as the heater voltage ramps up. Immediately turn the supply off if the voltage creeps past 6.3VDC, then adjust with the trimpot down to 6.2VDC.
The second thing I would do (to this and all other NU67 like it): remove the multi-resistor* network from the circuit board (lower right on your last picture), remove any resistors* from the XLR connector (second from last picture) and connect the power supply Tuchel audio connections (pins 1, 2) directly to the XLR connector (pins 2, 3) via an appropriate shielded three-conductor cable whose ground and shield are terminated together to ground on both connector ends of the cable
if you get -30 V at R9 the Zener is toast.If it would work it would limit the voltage to shortly above -15 V even without load.Replace it.
B+ = 217Heater = 6.52Close enough?
NigelT,I don't know a tonne about tube mics, but I do know that it's best for tube life to be conservative with heater voltages. 6.52 is 0.22v above the recommended 6.3v for an ef86.