12ax7 Tube Question

[Blood_mountain]

Hi Dudes,

I'm a tube noob, don't know a dang thing about them. I'm looking to possibly switch out the 12ax7 tube in my Two Notes Le Clean preamp for a vintage 12zx7 tube, because toanz. What am I looking for ideally? Are all Vintage NOS 12ax7 tube created equally? Particular manufacturers that are better than others?

Sincerely,
No-Clue Tube Noob

[coldbrightsunlight]

Does it sound bad now? If you like it why change

[Dandolin]

It could be me, but I usually notice more difference from swapping tubes in an amp than in the pedals where I've tried it (could be something about more gainstages) I think tube rolling in a tube preamp pedal might be in the category of head candy - you might get a more noticeable difference from running different gain level 12a_7s, like 12AT7s or 12AU7s in there--usually if you're looking to lower clipping levels. But other than that, maybe start slow. Where are you? If you're in the US, you'll likely find better deals on RCA, RAYTHEON, GE, SYLVANIA than Mullard, Amperex, Genelex, Telefunken, Siemens etc. But that's a sampling of the usual suspects. In other places, it's quite possibly a different case. I used to find good deals on EBay lots of tubes pulled from old organs....

Also, check for 12AX7 "synomyms" ie. workalikes like ECC83 (on those fabled Euro/UK valves). There are also alt naming conventions for mil spec tubes, but I've seen that moreso with power tubes....

Pretty sure an expert will jump in to nullify what I've said

[Blood_mountain]

It could be me, but I usually notice more difference from swapping tubes in an amp than in the pedals where I've tried it (could be something about more gainstages) I think tube rolling in a tube preamp pedal might be in the category of head candy - you might get a more noticeable difference from running different gain level 12a_7s, like 12AT7s or 12AU7s in there--usually if you're looking to lower clipping levels. But other than that, maybe start slow. Where are you? If you're in the US, you'll likely find better deals on RCA, RAYTHEON, GE, SYLVANIA than Mullard, Amperex, Genelex, Telefunken, Siemens etc. But that's a sampling of the usual suspects. In other places, it's quite possibly a different case. I used to find good deals on EBay lots of tubes pulled from old organs....

Also, check for 12AX7 "synomyms" ie. workalikes like ECC83 (on those fabled Euro/UK valves). There are also alt naming conventions for mil spec tubes, but I've seen that moreso with power tubes....

Pretty sure an expert will jump in to nullify what I've said

Yeah, I was wondering about that. I have just read that some folks swapped out the original tube and liked the sound better. I found a vintage Telefunken 12ax7 from an Ampex console for $60 CAD ($46ish USD), so I might try that out just to see if it makes a difference.

[crochambeau]

Pretty sure an expert will jump in to nullify what I've said

Nah, you got it. Though I would also argue I am not an expert.

Yeah, I was wondering about that. I have just read that some folks swapped out the original tube and liked the sound better. I found a vintage Telefunken 12ax7 from an Ampex console for $60 CAD ($46ish USD), so I might try that out just to see if it makes a difference.

Those can be pricey tubes, if you can carry that cost as pure experiment it may be well worth doing so. Do note, if the white paint exterior lettering is intact do whatever you can to AVOID TOUCHING IT. That stuff will wipe off like fog on a mirror, and if you're lucky enough to get undisturbed printing the considered "collector value" is greatly increased...

Anyway, back to the reply I was about to send on:

I have done my share of tube swapping, and am of the opinion that some circuits benefit from it more than others. I have no experience with your preamp, so, I'm not going to weigh in on that; but I do see they claim 200 volts on the anode, so it's probably worth the effort to experiment. It looks like it's mono, so balance between halves is not as paramount a concern as it is with hi-fi & amp stages.

That said, I have not done a lot of shoot-outs between old stock and more modern tubes, because, well... I don't want to spend cash on modern tubes that I do not at present need. I have done preamp tube substitutions in stuff ranging from studio gear to hi-fi, and I tend to think there is greater impact with respect to hi-fi, as at that point the valve is affecting the entirety of signal at the "introduction to room" stage.

You're going to get beneficial differences with the lower gain (12AU7/ECC82 & 12AT7/ECC81) tubes primarily where current capability (say, driving a transformer connected to a reverb tank - or driving a tank through a cap) is desired. They do offer lower gains (60 & 40 respectively against the 100 of a 12AX7 - IF MEMORY SERVES), which can prevent distortion in *following circuits*.

There are tons of tubes that will drop into that slot (200 volts is fairly mild, and should pose no restrictions), 7025 is the industrial designator (MIL-SPEC or JAN use both, if memory serves).

NOS tubes in the common types have been an item of widespread interest for several decades now. This means they've largely been picked clean and what passes for NOS these days is either not, or expensive (or both). Furthermore, it's my understanding that by and large any available JAN tubes are probably soft rejects and are therefore undeserving of complete adoration.

Am I sounding like a downer? I don't mean to - I just mean to say DO NOT OVERPAY unless you have tried said tube (as in, that exact tube) in your application and have observed first hand any benefits.

I swear, some things just sound good no matter what you stuff in them.

Without further ado:

Flat (or smooth) plate Telefunken are generally considered excellent. I've seen them branded Fisher (or other audio gear companies as well). Telefunken are easily identifiable by the diamond shape cast in the glass envelope between the pins.
Ribbed plate Telefunken are also good, gaining traction when clean flat plate examples started bypassing the $200 mark.
Amperex (Bugle Boy) are also excellent tubes, I've seen these in test gear before.
Mullard are, of course, another generally excellent breed, but I feel like we're starting to veer into "voicing" territory a bit (read as: consistency is not as prevalent). This is, of course, a completely subjective missive on my part..
RCA "black plate" are another highly considered tube, but in my opinion at this point we can just dip into the ENTIRE spectrum of U.S. consumer based tubes because it seems there are good and not so good examples of tubes across the board. I may be guilty of not giving the domestics enough consideration, but I am generally happy planting a GE, Sylvania, RCA, or any of the OEM labelled variants willy nilly.
I have some NEC tubes that are excellent as well...

But as with anything 50+ years old, there are more and more duds out there all the time, so use your ears.

TL;DR: try and find pull jobs from the HAM radio community, accrue a small collection, and give anything that costs more than a decent meal a listen to first whenever possible.

[Dandolin]

well, assuming the tube tests well, it won't hurt your pedal to try it. Preamp tubes tend to be longer-living than power tubes, maybe because, by virtue of their function, they are subject to less harsh conditions - I doubt it's because of any fundamental difference in construction or materials. Point is - it's pretty safe to try out, as long as you're matching up the right tube to the right circuit - that Telefunken may really please ya Even if it doesn't make much difference to you, you can probably re-sell it without taking a loss....

also - listen to Curtis, not me

[Blood_mountain]

These are them:

[Dandolin]

purty
60 bux a piece, or for the quartet?

[crochambeau]

These are them:

Those look like clean ribbed plate tubes, typically very decent and a joy to listen to. If they haven't been completely worked over.

I assume the $60 CAD is for one, if it's for the quartet you should probably just fucking buy them.

Preamp tubes do typically enjoy much better longevity than tubes that have to work hard. That said, they can go microphonic (via abuse while hot) or suffer filament failure, in addition to more visible failure modes.

[Blood_mountain]

These are them:

Those look like clean ribbed plate tubes, typically very decent and a joy to listen to. If they haven't been completely worked over.

I assume the $60 CAD is for one, if it's for the quartet you should probably just fucking buy them.

Preamp tubes do typically enjoy much better longevity than tubes that have to work hard. That said, they can go microphonic (via abuse while hot) or suffer filament failure, in addition to more visible failure modes.

It's $60 CAD per tube, and he just has two left. He said they've been tested with a pal's tube tester and they tested very strong with no gas or shorts. What should I ask specific to testing? I've read things like 59/60 but I don't really know what those numbers mean

[crochambeau]

He said they've been tested with a pal's tube tester and they tested very strong with no gas or shorts. What should I ask specific to testing? I've read things like 59/60 but I don't really know what those numbers mean

It's probably an emission rating. 59/60 is pretty even on both sides, so the tube is fairly balanced between the halves (again, probably not a concern in a pedal, but nice to know if you're planting this in the front end of a tubed integrated amplifier).

Test fine with no gas or shorts is about all I would concern myself with. You will not get meaningful characteristics from numbers (just my opinion), just like saying "yeah, the tires hold air just fine, and have a decent amount of tread" does not equate to mounting the tires to your car or bike and then finding a fun road to drive.

The type of tube under question is one I have experienced and found to be a decent one for my applications. I probably wouldn't plant a Telefunken in a pedal (my only tube pedal is nothing to write home about though) but only because I would prefer slotting that into a bigger fixed piece of furniture. Is that the same as saying these are a better use of the funds than two or three more pedestrian oldies? Hard to say. I would think that if you're comfortable swinging the money at it, they are a fine example of a vintage part. (assuming working order and honesty on part of the seller)

One of these years I really should do an extensive shoot out with older stuff and newer stuff and veer speculation closer to raw experience. I understand there are decent tubes enjoying current manufacture...

[Dandolin]

yeah, sounds like an emission rating.

[crochambeau]

yeah, sounds like an emission rating.

I guess I forgot to stress the fact that, by and large, emission ratings don't mean shit. They are almost a meaningless number.

I took a peek at my tester (EICO 666) to refresh my memory a bit since I'm mired in transistor stuff these days, and it measures on a MUTUAL CONDUCTANCE scale that puts 60 at the transition point between the RED - REPLACE zone, and the YELLOW - "?" zone; so I would ASSume that these tubes, having "tested strong" are using a different measure...

At this point I will also state that I think the mutual conductance measurements are also largely meaningless (in terms of the toans).

No shorts or soft/gassy vacuums is about the realistic extent unless the seller is standing behind their product and will let you ear test things it's going to be a roll of the dice.

[Blood_mountain]

yeah, sounds like an emission rating.

I guess I forgot to stress the fact that, by and large, emission ratings don't mean shit. They are almost a meaningless number.

I took a peek at my tester (EICO 666) to refresh my memory a bit since I'm mired in transistor stuff these days, and it measures on a MUTUAL CONDUCTANCE scale that puts 60 at the transition point between the RED - REPLACE zone, and the YELLOW - "?" zone; so I would ASSume that these tubes, having "tested strong" are using a different measure...

At this point I will also state that I think the mutual conductance measurements are also largely meaningless (in terms of the toans).

No shorts or soft/gassy vacuums is about the realistic extent unless the seller is standing behind their product and will let you ear test things it's going to be a roll of the dice.

Cool man, thanks for all the info! The dude is on the other side of the city, but I'll be up there towards the end of the week, so I'll probably grab one from him if he still has them. Seems reasonably priced compared to the rest of the vintage tubez out there.

[D.o.S.]

Yeah Tube rolling can be super fun but with the vintage shit it really does start to get into "can I tell the difference jamming with a band? fuck no" territory. But (especially in the '90s and early '00s) a lot of the easily available tubes were definitely a cut below the vintage ones. I'm not sure about what the market is like now because I haven't been playing my tube amp extensively for the last four years or so