Tube Replacement Problem - Audio Research SP9 MKiii- V1 Tube Goes Dark w/ new V2 installed


Hi, Does anyone have any suggestions??

I’ve tried replacing the original Sovtek 6922 V2 position tube with a vintage NOS 6DJ8/6922 Amperex SQ circa 1969, but the original V1 position phono tube goes dark and I get no sound from my turntable. The new tube in V2 position works fine and sounds terrific despite the no phono with the darkened Sovtek in V1.

However, when I go back to the original 6922s in V1 and V2 position everything works fine and tubes light as normal. Do the new tubes need to replaced as a matched pair or is there anything else that I should know about replacing a single tube?

The unit is a factory SP9 MKIII.
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Matching not needed! I suspect a poor solder connection on one or both of V1's socket's heater connectors to the pc board. That's why V1 won't light when you press the new V2 into its socket. Easily fixed - if you can get to the underside of that pc board and re-solder!
Try wiggling the dark V1 after installing V2. See if it lights! Cold solder joints can be intermittent! Tube sockets should not be soldered to pc boards! Poor connections can result!
Possibility 2 is that the old V1 has an internal bad connection to its heater. That is the simplest fix! Just install a new tube with a working heater! Try the wiggle test! A bad internal heater connection can be intermittent also!