Don't use a 6922 or variant 6dj8 or 7308! I would resist taking advise from this source. :-)
I just googled this issue - you may do likewise. You will note that the PV 10 and 12 come in three different versions; 1) PV10, 2)PV10A and 3)PV10AL. (Ditto the PV12)
The PV10 uses 12AX7's in V1 & V2, 12AT7's in V3 and V5, and a 5751 in V4. (Ditto the PV12)
The PV10A uses 12AX7's in V1 and V2, 12AU7's in V4 and V5 and a 12AT7 in V3. (Ditto the PV12A)
The PV10AL uses 12AU7's in V4 and V5. The other positions are unused. (Ditto the PV12AL).
The CJ site has a diagram of the tube sockets and designations.
Now all you need to know for sure is which model you are using. Obviously if it is the PV10 or PV12 you are for sure using the wrong tubes. Casousa would be right on!
BTW, I wouldn't suggest that you try to substitute 12AX7's for 12AU7's if the latter is the designated tube for the socket. Much too much gain. The obverse exchange might work well if you have excessive brightness due to a pre-amp/amp interface.
As I mentioned before, if you've got the right tubes in the right sockets relax and enjoy a probable better utilization of your attenuator.
