12 AX7 et all

[rloggie]

Would someone inform me if 12ax7 is interchangeable with either 12at7, 6201, or 12au7? Or direct me to some newbie type tube tutorial. This is for use in my preamp that uses currently 4 12ax7 for the line and 4 for the phono. Thanks for any info!!

Robin

[Marvel]

Short answer is no. This may help out a little:

12AX7A: ECC83, E83CC, 5751, 6681, 7025, 7058, 7729, CV492

12AU7A: ECC82, E82CC, 5814A, 5963, 6067, 6189, 6680, 7739, CV491

12AT7: ECC81, E81CC, 6060, 6201, 6679, 7728

12AV7: 5695, 6072, 6414

6DJ8: ECC88, 6922, 6211, 6N1P, 6N1P-EB, 7DJ8, PCC88 (the 7 volt versions work OK on 6.3VAC)

The Russian 6N1Ps have higher filament current requirements, 600 mA instead of 300 mA.

The 12AU7 also has 6, 7 and 9 volt filament versions. (6AU7, 7AU7 and 9AU7)

6BQ5: EL84, EL84M, EL84S, E84L, 7189, 7189A, 7320, N709, CV2975, CV8069, CV10321, 6P14P, 6P14P-EB (SV83, 6P15P)*

6BQ5 also has an 8 volt (8BQ5) and 10 volt (10BQ5) filament version.

* SV83 and 6P15P are similar, but have lower screen voltage ratings.

7247 and 12DW7 are equivalent (used in original Dynaco ST-35 and others) These are 1/2 of a 12AX7 and 1/2 of a 12AU7).

You can also download a program (free) from Duncan Amps, that lists specs, equiv. tubes, let's you do searches, etc. Tons of tubes in the database, and it runs as a single exe file. It is way cool.

http://tdsl.duncanamps.com/

Marvel

[lynnm]

Marvel

Thanks for the link !

[rloggie]

Yes, Thank you for the response. I'm a little long in getting back to the post.

Thanks again. Robin

[Dflip]

Some information about 12AX7 tubes and it's variations. The 5751 while good tubes and I do use them are rated at 70% or what 12AX7's are, so you lose a little volume (usually not a problem with the line stage, but may not work in the phono stage).

Information is from: http://www.audiotubes.com/12ax7.htm This is a commerical site and I have bought tubes from Brent before, but I am in no way connected to him. The information is strictly for your personal use.

12AX7: the original version of this tube. This can only be used in parallel filament circuits. This is not a big deal as virtually all audio equipment is of a parallel filament design. These often have large rectangular plates with several horizontal ribs. The older versions have blackplates, which are often preferred by audiophiles.

12AX7A: This version can be used in series or parallel filament circuits. These usually date to the 1960s and have greyplates. Vintage versions of these are about the most sought after tubes of any type today. Often RCA and GE made these for electronic organ manufacturers, and have the organ brand name on the label. These are usually specially selected tubes, and are a great buy---when available!

ECC83: This is the European version of the 12AX7, and is identical to it. Most tubes with ECC83 listed on the label are European, and the ones in demand are Telefunken, Amperex, Mullard, and Siemens. More difficult to find but worth seeking are German made Valvo and the early Holland made Philips Miniwatt and Philips "SQ". Telefunken tubes have a diamond shape molded into the glass on the bottom center of the tube. The most desirable of the Telefunken ECC83 tubes is the "smoothplate" or "flatplate" versions. Like the name implies, the dull grey plates are perfectly smooth. Amperex and Mullard tubes have a pair of alpha-numeric date codes printed in dark grey near the bottom of the tube. The rarest of these are the BugleBoy cartoon tube label for Amperex, and the older Mullard logo that looks like a shield, especially with the letters "BVA" below it.

7025: This is the low noise, "industrial" version of the 12AX7. This has a spiral wound filament which reduces hum and noise. These are usually the best choice for demanding hi-fi applications, although the premium brands and blackplate types also have very low noise.

E83CC, E803CC: This is a premium European version of the ECC83. These are rare in the USA.

B759: This is an ultra-low noise version of the 12AX7, with matched triode elements. To my knowledge, only Genalex (Marconi-Osram Valve Co.) made these in England for their "Gold Lion" series. Extremely rare in the USA.

6681: This is listed in some tube manuals as a "special 12AX7", otherwise the electrical specs are the same as the standard version. Being an industrial type it most likely has a ruggedized filament, and is built to withstand many on-off cycles. I believe only RCA made these, regardless of brand on the label. UPDATE: One astute customer has informed me that GE offered 6681 tubes with the typical top seams, date codes, and "Gt. Britain" marking that indicates English Mullard manufacture. Indeed, some GE 12AX7 and 7025 tubes from the 1970s were also Mullard made, so they must have made some 6681s for GE as well. Overall, the 6681 is an excellent step up in quality from the standard 12AX7, and is a bargain at current prices.

5751: This version was usually the one made for the US military. These have a lower gain than the 12AX7, but are otherwise totally compatible. Great hi-fi tubes, as the lower gain reduces noise and microphonics. These are all ruggedized and most can withstand a drop on the floor. The internal triode elements are matched as well. The early versions are more sought after as they usually have extra support rods and an extra mica spacer on top of the plate structure ("Triple Mica"), as well as blackplates, all said to contribute to low microphonics. Don't overlook the greyplate versions, they are also excellent tubes, and many of these have the triple mica as well. The GE non-military version is usually the "five star" series, intended for broadcast use. The RCA broadcast type is the "Command" series. Both the RCA and GE broadcast types are scarce, as are any of the triple mica types.

[thebes]

Marvel, thanks for the link. Downloaded the software and what a great little program. Not only can you find substitutes but links to sights that have info on the particular tube your looking into.

Now all I need is a virtual tube tester!