Fosgate Signature Phono V1 Preamplifier

I put in a Siemens CCA (6922’s) in the V1 and V2 spots, RCA 7025A in the V3 and a Telefunken Smooth Plate in the V4. For the V5 a Phillips 12AT7WC green lettering and in the V6 a GE Green Labeled 12AT7WC with white 6201 markings. The 6X4 tube is an El-Menco tube that says Made in Great Britain and has the classic four lines on the top of the tube. Still experimenting with those final three spots.

I use a Foz V2. 

Like everything audio, the tube/cable tweaks are a subjective, YMMV thing.

The manual states V3 makes the most sonic change.  After trying tubes in the other positions, I too agree it's the only position worth experimenting with. 

Whatever change the other positions offered,it was too subtle to bother with. I'm more concerned with tubes being as quite as possible.

Clean power(PS Audio Power Plant) and decent power cable are more  of an improvement in my situation.

ask Andy at Vintage Tube

You can use a 6ax5 as long as your transformer can handle 1.2 amps. The 50s Tungsols are very good also.