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I know the pins are different but how does it compare to a 12ax7 for tone or gain?

Very similar to a 12AX7 but is larger physically and is noted as a low noise, low microphonic tube. Closer to a 7025 in that regard.

Same tube as the 12AX7. but different pinout and designed for audio applications. I think that means low noise. I use them instead of 12AX7, depending on what I've got and what I'm trying to do. For the JTM45, I really wanted a Mullard and that meant using a 6EU7 for V1. There is some new production available. You can find old stock (used and supposed NOS) for less than the cost of a 12AX7, making it a bargain.

If you are someone who like the flexibility of being able to sub other members of the 12A?7 family, this tube has zero flexibility in that regard and it isn't for you.

I don't mean to be contrary, but I'm presently holding a Mullard 6EU7 and a Sylvania 12AX7. I didn't put a caliper on them, but they look to my eye to be the same size. It might be different for new tubes. I've never seen a new 6EU7.

I have two 6eu7's. Ones a Sylvania USA and the other is an RCA 70's style logo. I got them in a some kind of switch that I bought on ebay for the chassi and PT with all the hardware sockets and stuff.

I didn't know if these were worth keeping or what.

I built a HotBox with 6Eu7 and it sounded awesome...............like a really good 12Ax7.............the label had rubbed off but the Made in Grt Brittain was still there................I don't think they are Mullard (don't know if Mullard ever made a 6Eu7) but maybe Brimar...................who knows.They sound shweet.......besides having the heater pins just on one side makes it easier to wire.
Aharon

Aharon wrote:...besides having the heater pins just on one side makes it easier to wire.

Agreed!

At first glance ,looking at GE datasheets,everything is equal except the 6EU7 was designed specifically for audio and can take 330V in the plates,30V more than a 12Ax7.
Aharon

Aharon wrote:I built a HotBox with 6Eu7 and it sounded awesome...............like a really good 12Ax7.............the label had rubbed off but the Made in Grt Brittain was still there................I don't think they are Mullard (don't know if Mullard ever made a 6Eu7) but maybe Brimar...................who knows.They sound shweet.......besides having the heater pins just on one side makes it easier to wire.
Aharon

A Mullard should have a seam going all the way across the top.

These have seams.........alright!!!!!!!!
Is that true for 12Ax7s too?.....I have a couple of Rogers with seams and they flash when turning on.............
Thanks Phil_S
Aharon

I have a few old 6EU7s and they all appear to be a slightly longer envelope than 12AX7s.

dartanion wrote:I have a few old 6EU7s and they all appear to be a slightly longer envelope than 12AX7s.

Both of mine are slightly smaller diameter than a 12ax7 and one is the same length and the other is slightly shorter.

koffee_iv wrote:

dartanion wrote:I have a few old 6EU7s and they all appear to be a slightly longer envelope than 12AX7s.

Both of mine are slightly smaller diameter than a 12ax7 and one is the same length and the other is slightly shorter.

Weird...

dartanion wrote:

koffee_iv wrote:

dartanion wrote:I have a few old 6EU7s and they all appear to be a slightly longer envelope than 12AX7s.

Both of mine are slightly smaller diameter than a 12ax7 and one is the same length and the other is slightly shorter.

Weird...

Maybe mine are worth a gob of money! Trade you both of them for a Twrek kit...

OH WHAT A DEAL!!!

Your 6EU7s plus a few extra bucks!

dartanion wrote:OH WHAT A DEAL!!!

Your 6EU7s plus a few extra bucks!

Hmmm.... Since you want a "few extra bucks", they may not be as valuable as I first was hoping. Figures.... I never "find" those elusive treasures laying around. Even in my own family those deals happen around me. My sister-in-law several years ago sold an early 70's Gibson Hummingbird 12 string for $20 in a garage sale! Gee whiz, I'd of given her.... $25 or $26 bucks! Needless to say, I asked her to invite me over the day before her next garage sale!!

dartanion wrote:I have a few old 6EU7s and they all appear to be a slightly longer envelope than 12AX7s.

It may be that there is a long plate and a short plate issue of the tube and that could account for needing a larger envelope. Or maybe it's just a matter of when it was on the production line. As I was saying, just because mine are the same size as a 12AX7, doesn't mean the all are the same size.

I'll bet those are nice sounding tubes!

Both tubes are listed as outline 6-2, and there seems to be a range of about 1/8" tolerance in diameter and envelope sizes. I have NOS Sylvania 12AX7 and 6eu7, some are the same size, some are different!

cobalt

FWIW a guy where I work bought a Gibson Mercury this week, complete with original RCA 6EU7 preamp valves. Apart from the later of dust it was in amazing condition.

I have an old Davis PA el-84 amp I'll eventually convert to 18watt TMB thats loaded with I think sylvania 6eu7's. I like them alot

6eu7's are less microphonic true...but thats the only pro i see them having.They dont *sound* much different to me .If you are going to go NOS then use the 12BZ7 FAR better sounding than the 12AX7 and pin compatible with other 12A*7's.