It uses 2 12ax7s and 2 el84s. I suppose that the 12ax7s are in V1 & V2. El84s will take V3 & V4. Now the V2 will be the PI?
I have old stock tubes in the amp, Raytheon 12ax7 in V1 and RCA 12ax7 in V2. They're both black plates. Am I wasting the RCA using it as the PI?
The PI has nothing to do with tone, right? I heard that Sovtek 12ax7lps makes a good PI tube so should I put that in and save the RCA?
No, funny I didn't think of it. I have a box of used tubes, I guess I can use them and find out.
The Sovtek LPS is a great tube for circuits that aren't too sensitive to microphonics. They do deliver the high quality tone of better NOS tubes but tend to be to microphonic for V1 in high gainers. That said, I'll back the first response. Can you hear a difference. The PI IS amplifying and in many cases overdriving. There IS an audible difference between tubes. I take time with every amp I own to try a bunch of different tubes in each socket to find the best lineup. The amps I sell are designed using current production tubes that generally sound good off the shelf. But if you really want the best tone you need to go NOS and try a good handfull of tubes in each socket, and then swap them out and do it again. We're talking about pretty small gains here but it does make a difference. FWIW the RCA grey plates are my personal favorite preamp tube.
"If you don't already know that you can do this without killing yourself, or worse yet damaging the amp further, take it to a tech." R.G.
Having said that, because the PI is the driver stage, or at least part of it in cathodyne designs, long-plate 12AX7's offer the best detail and nice, open tone. In addition, PI's aren't prone to microphonic issues, so the Sovtek LPS works well, though my personal favorite at this time is the J-J, which is also a long-plate design. Incidentally, one of the reasons long-plate tubes are prone to microphonics is because of the increased plate area. They CAN work in V1 in piggyback amps, but in combos, it's NOT bloody likely!
John R. Frondelli
dBm Pro Audio Services, New York, NY
"Mediocre is the new 'Good' "
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