12AX7 tube comparisons

Here is a quick comparison of new 12AX7 tubes tried recently. All new tubes had at least 20 hours of burn in time on them.

From left, RCA 5751, Sovtek LPS, Tungsol re-issue, Psvane, GE Triple Mica Black Plate 5751. My morning cup of coffee just happened to be there. 

Tungsol re-issue (steel pin)

Following from my review of Tungsol's 6SN7, a quick audition of its 12AX7 brother suggests that New Sensor is going for a particular house sound with Tungsol re-issues. Predictably, the 12AX7 sounds smoother, richer, with more bass emphasis compared to its EH cousins.

The Tungsol has a creamy smooth midrange with a weighty and slightly rounded bass. The trade-off is comparatively less open highs. Brass instruments and the shimmer from ride cymbals have noticeably less rasp and decay. This also affects the retrieval of fine acoustic space. The lower register weight helps Piano notes though which have impact and good timbre.Resolution and dynamics are mediocre.

BTW, like the Sovtek LPS, don't chuck them out if they "fail" to light up. The filaments are so deeply recessed that the tubes do not glow when switched on.

Sovtek LPS

If the Tungsol is "night", then the Sovtek LPS is certainly "day". Not to be confused with the standard Sovtek offerings, the LPS is a Long Plate Spiralled filament version.

The Sovtek has a very tight and focussed sound, against a deathly quiet background. This is far from being a dark sounding tube. Bass is tight although not particularly extended. The midrange is forward and almost solid state like, but grain free. Highs are clear and extended. Dynamics are first class. On the downside, the Sovtek tends to emphasize voice sibilance. When the mix gets really heavy, separation of instruments also tends to fall apart.

Put into perspective its low price, this is an excellent tube that is actually better than a lot of the ho-hum NOS tubes out there. It is not the best available, but could be just the ticket to opening up a dark and slow sounding system.

Psvane

A premier offering from Shuguang, the Psvane (as well as Shuguang's power tubes sold under the Black Treasure series), is sold with eye-popping prices (for a Sino tube) and rather fanciful (but ultimately useless) foam lined cardboard box with individual test results and serial numbers.

Psvane signal tubes (I had a roll with its 12AU7 brother too) seem to have one thing in common - tonal density. These are not insipid or wispy sounding tubes. They have a strong and full flavour. Bass and midrange are full and smooth. Coupled with good high frequency extension and good separation, they are well balanced and good overall performers. They are also quiet and refined sounding. Top marks for composure - they never lose their cool, even under complex and messy mixes.

In terms of ultimate high frequency extension and speed, the Sovtek LPS have an edge over the Psvane. The Psvane also tends to deliver larger than life images - perfect for the SET / full range speaker crowd.

If its tonal balance suits you, this is a very nice tube. Objectively, it is head and shoulders above most current production tubes (and it should be - with a matching price tag). However, I could think of a few NOS tubes that could blow it out of the water, or at least give it a serious run for the money.


RCA 5751 double mica black plate / GE triple mica black plate

OK. The 5751 is not a 12AX7 tube. They have slightly lower gain, but other than that can generally be used as a substitute for 12AX7 tubes in buffer and line level applications. My tubes were bought NOS from a well known local dealer and have at least a few hundred hours on them. They are featured here as a comparison between new tubes and NOS. Price wise, the Psvanes are almost as expensive as the RCAs.

The RCA has a nice big and wet bass. It has a rich and creamy midrange which controls sibilants well. On the  downside, brass lacks bite and dynamically, this tube sounds a little bit slow. In comparison, the GE triple mica 5751 grey plate or the Sylvania triple mica gold pins are significantly faster and more open. Rather unfortunately, the tubes mentioned have become horrendously expensive as of late. For the money, I would pick the Psvane over the RCA.