In his review of the BHK 250 in Positive Feedback Dave Clark indicated Kevin Deal suggested the PCC88/7DJ8 for the 6922. He tried them and noticed modest but welcomed improvement. I rolled in a couple recently from the Tube Store and like Clark I notice a modest but noticeable improvement; a bit more air around instruments and instrument groupings in orchestral recordings and slightly greater depth to the sound stage. The improvement is small but heard on multiple recordings.
Was the 7DJ8 old production and the 6922 you substituted for new production? If that’s the case then part or most of the improvement you heard may be attributable to that. For example, a new production Gold Lion 6922 versus a Siemens 7DJ8/PCC88 are different in more than just tube type.
They were both NOS.
That definitely helped level the playing field and if they were both the same maker then even more so.
One difference between a 7dj8 and 6922 tube is that the 7dj8 is a 7 volt
cathode heater…Used in a 6 volt circuit should extend the life of the
filamint or so I have read another is that the 6922 is a premium version of the 6dj8.
For a more complete run down on the 6dj8, 6922, 7308 variants…go to
the Brent Jesse site via the link below.
Have fun reading.
Best wishes everyone
Thank you for the follow-up,
When I owned tubed equipment I had two preamps that used tubes from the 6DJ6/6922/7308/7DJ8 family (Conrad Johnson Premier 17LS and 16LS2) and one of their amps (the Premier 140) that used one as the input tube. I found that the 7DJ8 sounded (to me at least) just like the 6DJ8 of the same brand but was considerably less expensive when dealing with brands like Siemens, TFK, etc.
Over the years I’d purchase tubes of all sorts from vendors including Brent Jessee and there are certainly days when I regret having sold that equipment.