Best 12AX7/7025 Brand for reliability..

[jpdesroc]

Hi,
I'm about to buy some spare 12ax7/7025 tubes
from a local seller..
For low microphonics, gain & long life reliability
what are the best choices in the following list I'm offered:

Sovtek       12AX7WA/7025
             12AX7/6N2P
RCA          12AX7 Black Plate
             12AX7 Grey Plate
Westinghouse 12AX7 Black Plate
             12AX7A/7025A Grey Plate
GE        12AX7A/7025
             12AX7WA
             12AX7WA Grey Plate JAN
        12AX7 Black Plate
             12AX7 LONG Grey Plate
Tung-Sol     12AX7 D-GETTER
Sylvania     12AX7WA JAN
             12AX7 Grey Plate
Rogers        12AX7
Amperex      12AX7A/ECC83
Brimar       ECC83/12AX7

Thanks !

[alerich]

If it were my purchase and he has them I would get RCA grey plates with the short plates. I love them. They sound great in everything I plug them in from Fender to Soldano and I've never had one die or go microphonic on me and they last forever. Some of the Westinghouse 12AX7 branded tubes out there are actually Ei Yugo pre war tubes made on old Telefunken machinery. If you get a good one they are great tubes but they have been hit or miss for me in regards to microphonics.

The problem with old NOS glass is that much of it has already been picked through and the stuff that is being sold these days is the chaff. There are a lot of mediocre tubes being sold today simply based on what is etched in the glass. If someone unearths a case of untouched tubes these days they usually command car payment sized prices. If the guy is local and you can I'd take my own amp and try them before I buy them.

[eleventeen]

It really depends on whether they are loose tubes in a cigar box, NOS, or "used" in newish looking boxes. I have some very weak RCA 12AX7 and 12AX7A...the 12AX7 [not A] came out of an old Dumont scope and they have almost nothing left. I imagine everybody has a different story. I have bought new Electro Harmonix branded tubes at Guitar Center that were just great, and they cost 1/4th or 1/5th of what a knowledgeable seller will want for RCA 12AX7s. You could buy Tung-Sols made recently (meaning Russian) and get three or four different types. You could buy Westinghouses and probably get three different kinds. All things being equal, I have always liked the (genuine) RCAs, of course, followed by the Sylvanias, followed by GEs. Amperex are fine, Telefunken are fine.


In this circumstance, it behooves you to know, for example, the relative vintages of the types of paint/logo that *should* be present on RCAs. White > Red > Red "modern" logo.

Also, consider the tube caddy of an old style TV repairman. And sometimes you see these for sale. Well, if they are from the "series-filament" era then you could buy one of these and not have a SINGLE tube of any utility. Maybe you get a 6U8 or two. Or a nice collection of 6AL5's. Equally important, what are you going to see when you look at such a thing? A bunch of good looking tube boxes. How many of those are tubes where the repairman took the new tube out of the tube carton, installed it, and put the dead one into the same tube carton? Now, 45 years later, the children of the repairman are selling the caddy and they think all those tubes are new.

[HotBluePlates]

For low microphonics, gain & long life reliability
what are the best choices in the following list I'm offered:

Your choice depends on your wallet and subjective preference.

Which is best for "low microphonics & gain" is a trick question. They're all 12AX7's, so all have the same nominal gain; variation above & below the nominal gain is normal and can't be determined except by testing the individual tubes offered in-circuit. So gain is sample-dependent.

"Low microphonics" is similar. Tubes with the shortest plates and heaviest support structure have the lowest risk for microphonics. But that doesn't mean longplate tubes will have microphonics; it's sample- and application-dependent. Not every tube will be microphonic, and even a tube that's microphonic in one amp may not be in a different amp with a lower gain structure or better isolation from speaker vibration, or even in a different socket in the first amp with less amplification afterwards.

As for "long life reliability" ... I've had a bunch of old-production 12AX7's over the years, some as long as 20 years. I've never had a preamp tube fail outright. Most of the 20 year old tubes can be popped into an amp and perform as well as any other tube. Some might exhibit a hair less gain from the long wear, but you won't notice it without plugging a tube in with higher gain.

The truth is, most tubes will last an inordinately long time unless they're on 24/7, or unless you play in a band with multiple gigs per week, every week. The 24/7 tubes may eventually have cathodes that fail to deliver enough emission to perform to the fullest, while the gigging band may have tube failures mainly from being bounced around hard & frequently.


Maybe the seller has a tube tester and will give you measurements. The secret is, almost all tube testers are difficult or impossible to accurately calibrate, and the tester's results may be difficult or impossible to translate into a statement of the tube's performance. Testers of the same brand and model will almost always give different results even when testing the same tube. You don't have to believe me, read Alan Douglas' posts on the Antique Radio Forum; he quite literally wrote the book on tube testers (as an internet search will show).

At best, tube testers give an indication of a tube's condition, while the tube's performance must be assessed in the circuit in which it will perform. Even Hickok's manuals tell the user to test tubes in-circuit before deciding one is weak or should be thrown away.

[Mike_J]

For low microphonics, gain & long life reliability
what are the best choices in the following list I'm offered:

Your choice depends on your wallet and subjective preference.

Which is best for "low microphonics & gain" is a trick question. They're all 12AX7's, so all have the same nominal gain; variation above & below the nominal gain is normal and can't be determined except by testing the individual tubes offered in-circuit. So gain is sample-dependent.

"Low microphonics" is similar. Tubes with the shortest plates and heaviest support structure have the lowest risk for microphonics. But that doesn't mean longplate tubes will have microphonics; it's sample- and application-dependent. Not every tube will be microphonic, and even a tube that's microphonic in one amp may not be in a different amp with a lower gain structure or better isolation from speaker vibration, or even in a different socket in the first amp with less amplification afterwards.

As for "long life reliability" ... I've had a bunch of old-production 12AX7's over the years, some as long as 20 years. I've never had a preamp tube fail outright. Most of the 20 year old tubes can be popped into an amp and perform as well as any other tube. Some might exhibit a hair less gain from the long wear, but you won't notice it without plugging a tube in with higher gain.

The truth is, most tubes will last an inordinately long time unless they're on 24/7, or unless you play in a band with multiple gigs per week, every week. The 24/7 tubes may eventually have cathodes that fail to deliver enough emission to perform to the fullest, while the gigging band may have tube failures mainly from being bounced around hard & frequently.


Maybe the seller has a tube tester and will give you measurements. The secret is, almost all tube testers are difficult or impossible to accurately calibrate, and the tester's results may be difficult or impossible to translate into a statement of the tube's performance. Testers of the same brand and model will almost always give different results even when testing the same tube. You don't have to believe me, read Alan Douglas' posts on the Antique Radio Forum; he quite literally wrote the book on tube testers (as an internet search will show).

At best, tube testers give an indication of a tube's condition, while the tube's performance must be assessed in the circuit in which it will perform. Even Hickok's manuals tell the user to test tubes in-circuit before deciding one is weak or should be thrown away.

Agree to everything HBP said above.  I would add in my experience when buying NOS or old pulls I look for tubes where both triode ratings are very closely matched.  My theory, be it right or wrong, is if it has been used a lot then one of the triodes probably got more wear than the other.  If a tube tests strong and both triodes are closely matched then you have a good chance of being able to use it somewhere in your amp.  Like others have said it is hard to beat RCA tubes.

If you plan on buying a lot of NOS tubes it might be a good idea to buy a tube tester.  I bought an old Hickock unit probably 15 years ago for $200.  While the ratings I get would have little value to anyone else because who knows how well calibrated it is, it is a good tool to have because after you have tested enough tubes you get a good idea where different tube brands should test and of course you can verify if they are reasonably matched or not. 

An advantage to buying pulls that test strong is they in my opinion are less likely to be microphonic versus some of the culls that are out there as NOS.  They also cost a lot less than the NOS tubes do.

Thanks
Mike