NOS GUIDE NOS stuff....usefull information
you get from a N.O.S THAT sound that you're after....but not always ....
The 12AU7 is a medium-mu twin triode miniature glass tube. In most circuits it is used as a class A amplifier per triode section. This
tube has been, and still is, widely used in the preamplifier stages of high fidelity audio equipment, musical instrument amps, public address equipment, and broadcast equipment. It was used in so many different types of equipment that the vintage versions
of this tube are still available without too much searching. Like their cousin, the 12AX7, the premium USA and West European brands are being hunted to extinction, but there are still bargains to be had in other vintage USA brands. Here is the list of what
is available in the 12AU7 family:
12AU7 / 12AU7A: The common USA version of this tube. The 12AU7 can only be used in parallel filament circuits.
Like the 12AX7, this is not a hassle since virtually all hi-fi tube amps are of the parallel filament design. RCA, GE, and Sylvania actually made most of these tubes, regardless of brand on the label. The early RCA version has ribbed flat black plates with
a top getter and a white label. This is an amazing tube, one of the best USA 12AU7 tubes ever made and we have a good stock of these. Still available, and still a bargain since everyone wants the "cleartops": 1960s versions that have greyplates and the getter
on the side, making the top clear. These "cleartops" are currently the hottest selling 12AU7, and are still a great buy at current prices. Watch this tube....I predict in 5 years it will be as hard to find as the Telefunken smoothplate, and just as expensive!
The 1970s new logo version (and the late 1940s-1950s version with the white label) of the RCA 12AU7 has greyplates and a top getter. This greyplate RCA is about the best bargain you can get in a vintage RCA 12AU7. The GE versions pretty much always used greyplates
and a top getter for this tube. The numbers are etched into the glass with a pattern of dots below the number. Don't miss trying the "organ stock" 12AU7 tubes that were sold to organ manufacturers. These sweet tubes were screened for audio use in organs, and
have the organ brand on the label. Usually sold at bargain prices because of the re-branded label, the RCA cleartop and Raytheon blackplate versions are a great find! Tung Sol made an early "blackglass" version in the late 1940s, which hides the inside of
the tube from view, and is very rare; later Tung Sol 12AU7 tubes look like early RCA greyplates inside. All of these vintage tubes used a chalky label paint, and often the tube label is smeared or partially rubbed off. This does not indicate use or poor quality.
Rather, it is an indication of a genuine vintage tube, and all of these are excellent quality.
ECC82: This is the European version of the 12AU7, and is identical to it. The brands in demand
are Telefunken, Amperex, and Mullard. Telefunken tubes have a diamond shape molded into the bottom of the glass. Both ribbed plate and the more famous smoothplate types are available, just like the 12AX7, but are being hunted down and soon may be an endangered
species. Amperex and Mullard have tiny date codes etched in the glass near the bottom of the tube. The most popular Amperex are the Holland made Bugle Boy series, with the tiny cartoon tube blowing a bugle on the label. They later went to just a white label
that said "Amperex", and then after that used the orange label with the world logo. The earlier Mullard tubes had the word "Mullard" inside of a shield logo, later versions said "IEC Mullard". Watch for the very rare long plate versions from the 1950s available
in most European brands. These had narrow plates that were about 3mm longer than the 1960s and later versions. The earliest had square shape top getter elements, late longplates have a halo top getter. Even rarer are the Mullard and Amperex made CV491 longplate
square getter tubes, made only for the military. Most of these early Mullard tubes can be spotted not only by the date codes and longplates, but by the distinctive "wrinkle" glass, where the surface of the glass tube is not smooth but rather has tiny wrinkles
or sometimes an eggshell texture. These are all tubes of unequalled quality, and are worth the high prices they are commanding these days. Even used ones will blow away any of the trashy tubes in production today. Vintage versions again used the chalky paint,
and frequently the labels on any of these tubes are usually smeared. Other versions to watch for are the rare medical/hospital grade tubes, often with "Electronics For Medicine" or Tektronix brand labels, but still have the Amperex or Mullard factory codes
on the glass. Another rarity is the Amperex Bugle Boy with thhe treble clef sign next to it on the glass. These audio screened tubes were only made from about 1961-1963 and are worth the extra cost in their superb sonics.
7316:Simply an amazing tube. Amazing both because it sounds so incredibly good, and amazing how rare it is today. The 7316 was made by Amperex in Holland, I have never seen this in any other brand, nor have I seen it made by Amperex
North America. It is a medical grade/aircraft equipment grade super low noise tube, not sold to the general public. It is Amperex's answer to the ECC802S produced by Telefunken, and the 10M series made by Mullard. Most have the Bugle Boy on the label, although
I have seen plain Amperex labels, and OEM labels such as Beckman Instruments. The 1950s vintage with the long plates and D-getters are to die for. They are among the best sounding and rarest 12AU7 around today. Don't miss the 1960s halo getter version of this
tube, as well. They sound nearly as good as the D-getters and are usually half the price. Very few dealers ever have the 7316 of either type in stock, well worth seeking out and worth the higher price. We try to keep a few of each type in stock, but it is
not easy. Better buy them when you can find them!
CV491:A military specification version of the ECC82. These are usually found in Mullard or Brimar versions, but I have seen Siemens as well, and
some made by Amperex. This tube was made into the 1990s so careful selection needs to be made. The best are the Mullard and Amperex longplates from the 1950s, which look identical to the longplate ECC82. Ei Yugoslavia made a nice smoothplate version into the
late 1980s which sounds surprisingly good despite it's late vintage "East Europe" stigma attached to it. Overall, these are a step up from the standard ECC82 tubes, since they have military specs.
is a military spec tube. Sometimes the vintage GE versions may be labelled JG-12AU7WA in white and have 5814 etched into the glass. These are all low microphonic thanks to their rigid mica supports. Older versions have a third mica spacer near the top. These
"triple mica" versions are in great demand today. The broadcast versions of this tube are the GE 5-star, and the RCA Command series. These vintage tubes have just started to become a hot item, as NOS stocks of the West Europe types become harder to find. These
tubes can withstand many on-off cycles and mechanical shock without a problem.
6189 / E82CC: This can be both a military spec tube and a premium industrial tube. Often, the military versions
will be marked 12AU7WA in addition to having 6189 etched in the glass. The older vintage of these tubes are usually blackplate with the extra "triple mica" spacer at the top. GE made this in their 5-star line for broadcast. The RCA military 6189 is gold lettered
12AU7WA, has blackplates, and extra support rods. These are excellent step up tubes in the 12AU7 family, when you can find them! Look for super rare triple mica versions from Mazda, Siemens, and Mullard, some with silver plates. Among the best 12AU7 tubes
5963: This is a nice industrial type which is nearly identical to the standard 12AU7. RCA made a nice blackplate version of this tube, Sylvania has a gold pin version, and GE has
it in their 5-star broadcast line. The plate voltage rating is a little lower than for a 12AU7, but for most applications, it will work fine. It has a rugged cathode and should be long lived, similar to the 5814. Watch this tube, as it is plentiful now and
prices are low. As audiophiles discover it, the rush will be on!
6350: This tube was mainly manufactured for IBM and other computers in the late 1950s to mid 1960s. Sylvania and GE blackplates
are considered the best of all with this tube. The only difference is the pins that correspond to the grid and plate of each triode are reversed from the 12AU7 connections, so you will either need to rewire your sockets to take this tube, or consult with the
manufacturer of your unit to see if this tube can be used as a sub for the 12AU7. It has a mu or gain factor of 18 so is very close to the 12AU7. These were made to tight specs and carefully quality checked, since replacement in a computer of the day was difficult
and costly, and the tubes were expected to operate 24-7. These make impressive upgrades to the standard 12AU7!
6680: Motorola and GE are the brands you find most often with this tube, but RCA
made a nice cleartop version for a very short time. It is identical to the 12AU7, but has the added benefit of being able to withstand variations in filament voltage without affecting it's output. This tube was designed originally for two-way mobile radio
use. It makes a fine hi-fi 12AU7 tube as well. Never as plentiful as other types, this tube is rather scarce today.
7730:An excellent USA made industrial version of the 12AU7, produced mainly by
CBS labs but I have seen it with other labels as well. This tube has thickly plated gold pins and was designed for critical aircraft and other exacting industrial applications. It has a long life heater, is extremely well balanced and a top choice for audio
use. Very rare today.
ECC802: This is a premium version of the European ECC82, with matched triode sections. These are very rare in the USA, and often command very high prices.
E80CC / 6085:This unusual European tube is basically an industrial type 6085. However, it's specs are similar enough to a 12AU7 that audiophiles are grabbing them up while the prices are still reasonable. The heater
life is rated at 10,000 hours, and some have gold pins. The larger box plate structure gives this tube low microphonics and silky smooth sonics. Some of the Philips Holland versions had the rare pinched waist, where the glass dips inward and actually molds
around the top mica plate, giving the plates extra support and virtually eliminating microphonics. There is also a version made at the Amperex factory in Hicksville, NY, which is often priced lower but looks the same and sounds very similar to the Holland
version. Since this tube has a much higher Gm and Mu factor than a 12AU7, the gain is going to be greater and this tube will give a more forward presentation. Awesome in phase splitter applications. If in doubt, check with your amp or preamp manufacturer to
see if this tube will work OK in your application. This tube is also about twice as tall as a 12AU7, so installation space in your chassis is a consideration as well. These are out of production, rare, and getting very hard to find. The European types usually
command the top prices, but USA types exist as the 6085 and should be a bit lower in cost, but they are also rare and climbing in price. Many USA tubes were actually made by the European factories, so watch for the 6085 USA brands!
B749:This is made by Genalex (Marconi-Osram Valve Co. of England) and is extremely rare in the USA. The B749 is in the "Gold Lion" series of audiophile tubes, and has the gold lion and gold script on the glass. Inside it looks similar
to a Mullard 12AU7, and has a red Genalex decal across the bottom. These are said to sound the best of all 12AU7 types, and this reputation, coupled with it's overall scarcity, has driven the market price of this prize tube to extreme heights. Worth seeking
out as these may be the first out-of-production classic European tube to go totally extinct over the next dozen years or so.
OK, SO TELL ME HOW THEY SOUND!!
A tough question if there ever
was one! The best advice is to get a few types and hear for yourself the good sounds you have been missing. All of these vintage tubes are excellent, much better than the Russian or Chinese yuck that is being made today. When replacing any stock Russian, Chinese,
or East Europe tube with any of these vintage NOS types, you will notice immediately that the midrange glare is gone. Gone too is that honky, boxy quality, and the tiring upper midrange screech that current production tubes are famous for. Here are some VERY
GENERAL observations about some of these vintage tubes:
TELEFUNKEN, SIEMENS, VALVO, LORENZ, and other German made NOS: These tubes are usually characterized by an impressive open "air" at the
top end. The soundstage is large, even in mono applications these tubes have a great 3-D image. The midrange is ruler flat, and the bass is tight and accurate. For phono grade and critical high gain applications, the Siemens Nickel Plate and the Telefunken
smoothplate or ECC802S are awesome. These tubes have a fine sense of dynamics, and most are impressively quiet. These are not "warm" tubes, and to some ears their lack of midrange warmth may be heard as bright. I tend to think of them as accurate, and their
clean, focused sonic image is astonishing. My personal favorites.
AMPEREX, PHILIPS, MAZDA and other Holland/France/Belgium made NOS: These tubes are a great balance of a clean, airy top end,
nice midrange warmth, and accurate bass. They are very pleasant, clean, and musical to listen to in hi-fi applications. Unlike other clean European tubes, these break-up impressively when overdriven in a guitar amp. The rare longplate versions are the same,
but with even more soundstage space and detail. The USA Amperex factory tubes have a bit more detail and analytical focus while the Holland tubes are sweeter, both have great air and space. The Mazda adds a nice bit of dynamic punch to the sound.
MULLARD, GENALEX, BRIMAR, and other British made NOS: Like a warm British jacket of the finest tweed, these glorious tubes have an attractive sweet warmth in their midrange and lower regions. The top end is silky
and pleasant, without being rolled-off. The best of these tubes retain a fine sense of "air" at the top, and the upper midrange is smooth and liquid. These tubes reproduce the human voice, especially female voices, with haunting realism. The rare longplates
and Genalex versions have an eye-popping huge soundstage, razor sharp focus and detail, and an uncolored top end while retaining the warmth of the lower priced versions.
RCA, RAYTHEON, GE, SYLVANIA, and other USA
made NOS: This group is very diverse. The RCA, Raytheon, and Sylvania blackplates are among the best here. These are very musical tubes with air and sparkle at the top end, warmth in the mids, and great bass. The RCA are drop dead beautiful
in guitar amps, even the lower priced greyplate and longplate versions. They also have a wonderful "phat" gritty sound when overdriven in these amps. Check out the RCA cleartops, they are a knockout at their current price, about half that of a NOS European
tube! The blackplates and most tubes made for organs are very quiet. The greyplate GE is an all-around nice-guy tube to listen to, the 5814A here possibly getting the nod for hi-fi use. The Sylvania greyplate and military versions are clean and a bit bright,
but the 5814A versions are very accurate. The RCA 5814A is more like the Mullard, with a rich warmth and wide bandwidth. Currently, the USA made tubes are a nice surprise with their low prices as compared to the European types.