12BZ7/12AX7 vs. 5751

I have a Cary V12 with 12BZ7 tubes in the input. I read an article last night that suggest that the 5751 is interchangeable, just with less gain, and that it sounds significantly better. Has anyone used a 5751 in place of a 12BZ7, or for that matter a 12AX7, and could you comment on any differences/improvements in sound?

I've read in several places that the 12bz7 is not a direct replacement for a 12ax7. I don't have the tech chops to fully understand why. You should check with Cary before making a change.

Perhaps new speakers would make a more substantial improvement.
I have an Octave V70SE that uses a 12ax7 input tube and swapping it out with a 5751 was an improvement over the stock tube. I heard no loss of gain. I have learned from experience that the input tube makes the biggest difference. Here is a recent discussion.


That being said it never hurts to ask the manufacturer.
As a retailer, I'm sure you'd think so.
Why in the Sam Hell would you be rude enough to suggest new speakers? Grimace never mentioned speakers just a simple question about tubes.

Grimace sorry I can't answer your question but I do know 5751's are a replacement for 12AX7. I would contact Cary and Google search. I saw some very good advice awhile back on interchanging tubes but I do not remember where. Sorry.
While I have never used a 12Bz7.I have tried NOS low noise, matched,(read expensive) 5751 tubes in place of the 12Ax7 that were stock in my Tron preamp.After about one month of listening I placed the 12Ax7 back in the Tron.
My conclusion was that the 12Ax7 gave more body to the music,with better dynamics,separation of musicians and wider stage.Others may say that my conclusion is wrong Joe's Lore) but this is what I heard in my room with my components.YMMV
Sam, thank you for the backup. Clearly one of those salesmen who wonders why he never sells anything.

I went to my favorite secret old TV store with thousands of tubes lying around looking for a pair of 5751s, but he didn't have two. However, he did have an NOS pair of GE 6BQ5s which - probably because they're fresh - are a bit of an improvement over the old Mullard EL84s. So... you never know what you're going to find.

I just don't get the whole tube rolling deal.
"I just don't get the whole tube rolling deal."

I must respect your opinion since you are a dealer, with lots of experience I presume. I will put aside some thoughts I might have, being on the other side of the coin.

But I would like to understand your recommendation since you went directly to the speakers. Why not the source, the amp, cable changes, room or power source treatment ? Can you explain why go immediately for an expensive solution ?
5751 sound thin, if you like a more solid state sound then go 5751's. Joe's Lore is what he heard in his system with his ears and his likes. Nothing wrong with that, but it does not make for in stone what tube is the best for your system and your ear and bias.
surprising comment " i just don't get the whole tune rolling deal" given sounds real audio that you sell tube gear - try it you might be amazed
Not getting the "whole tube rolling deal" is like "not getting the whole appreciating differences between things deal." Also, I'm a believer in 7025s as a 12AX7 swap, although results may vary. Is an accurate and full range tube tone a "SS" sound? This term is bandied about by term bandiers suffering from adjective deprivation. I prefer my music to sound tonally correct using my extremely refined ear, impeccable taste, serious demeanor, and finger burning tubes glowing for my amusement and aesthetic needs. Both ears actually, especially when they're clean-ish.
I can't comment on whether 12bz7 is a substitute for 12ax7/5751 however if it is my advice would be take advice only from those who have experience of your amp or go out and listen for yourself.

For me Sylvania 5751 are excellent, better than any 12ax7 I've tried but in another implementation they may not work at all.

Can be good fun exploring different tubes though expensive and a good measure of frustrating
Hi Grimace

I have been swapping 12AX7 tubes with 5751 type tubes in a Jolida Glass FX tube DAC. The RCA Grey Plate 12AX7 tubes from the 70s I had in the DAC made the music very forward and cymbals and highs really had some sizzle to them. Music was borderline unnatural sounding. I rolled in some JAN GE 5751 type tubes from the late 80s and it made the music less in your face and calmed down the highs by wide margin.

I'm going to try to find Sylvania 5751s at a good price but they seem to be getting scarce. There are a lot of GE 5751 tubes out there for you to choose from. Lastly some tube sellers have low gain options for 12AX7 tubes BUT from what I've seen these are for newer issued tubes. E.g. Sovtek, JJ, Tung Sol. I don't know if that could be another solution for you.

Good luck.