Fosgate Signature Phono V1 Preamplifier

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

ask Andy at Vintage Tube

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.

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 have found my Fosgate to react to any and all changes, this would include duplex outlet, power cord, interconnect, and also changing the fuse to the Synergistic Research Black fuse made a noticeable difference. I am currently considering trying the Orange fuse.

Also I have found that every tube change makes a difference, V3 may very well show the largest difference but I hear a difference with every tube changed. Currently the only stock tube I am using is V1, but if I put on a different cartridge that would most likely require some tube change.

I can't address your question about the SER and bass as that would require changing back to the stock Rectifier tube, just give it a try and see how you like it.

I have owned this for a long time and think it can sound fantastic, with a great sound stage. My only complaint is its not having enough gain for most MC cartridges. 

Gary

Thanks Gary, I am leaning towards the SER but still open to suggestions from owners of the Fosgate V1. I might try the SER and one other. How did it handle the bass. Also did any of the other tube changes make a difference? I read that only the V3 position 12AX7 will.

I own the same Fosgate V1 as you, a couple years back I bought the 6X4 SER Rectifier Tube. It seemed to make the sound smoother, less edgy. I liked it enough that I bought another for a backup.
 
That said I have made many tube changes of the other six tubes since and I have not tried listening with the stock 6X4 with my current tube setup.

Gary