12AX7 .... New versus NOS ... Sovtek 12AX7LP versus Telefunken

[myles_rose]

Telefunken 12AX7 versus Sovtek 12AX7LP and 12AX7LPS.

 

Testing completed at Guitar Amplifier Blueprinting 3/4/02.

 

There are many tubes today that state that they are close to the original sound or construction of the older Telefunken tubes and Mullard tubes.

 

This tube from Sovtek claims neither, but it has received some very good reviews, so we opted to test this tube against the classic curves of one of the standards, the Telefunken. In tests at a later date, the Electro Harmonix 12AX7EH will be put up against the Telefunken, as the do say that the two of them are supposed to be very close.

 

There will be a link put in this report later, that will take those that wish to see, the graphs and notes made during the testing. Its messy and hard to read, but I can assure you I am organized during the tests.

 

This Sovtek tube comes in two versions; the LP and LPS. The LPS has a spiral heater that is supposed to reduce hum in circuits that use AC heaters. It was noted that in some amps, they did make a difference. It was also noted that in some DC heated amps, they induced a little noise under some circumstances. It would pay to know if your heaters are AC or DC if selecting this tube.

 

Guitar amplifiers vary quite a bit on the plate voltages supplied to their preamp tubes. In some of my Fender amps, it is 170-180 volts, and in some Mesa Mark series it is 245 volts. This particular tube did not respond at lower voltages nearly as well as the Telefunken. With a -2 volt bias, there was virtually no useable output until the plate voltages approached over 225 volts. The bottom line here: This tube does not work in a Fender Deluxe circuit if the volume is set to "4" or less. Even at higher levels, it did not have the musical detail of the NOS tube.

 

The curves and traces on the Sovtek were fairly good, but not anywhere close to as linear as a Mullard, Telefunken, or JJ ECC83. I think the reasons for this could be that the cathode coatings are not as pure as in those other tubes, not the same formulations, not applied as carefully, or the process was perhaps rushed. This was also borne out in the differences between the various tubes in the samples. There was a wider degree of inconsistency than in some other tube brands and types.

 

This is a good tube though. Sonically it is a nicer tube than a Sovtek WA or WB at higher volume levels. The WA and WB from Sovtek proved to be very sturdy and non-microphonic, and at lower levels in the Fender circuit, did sound better to the majority of players who voiced their preferences.

 

Bottom line: This tube is not as smooth or sensitive to touch and dynamics as some others. At lower levels in amps with moderate gain front ends, there are better choices. The choices that the folks around here picked in some Fender, Marshall, Rivera, THD, Matchless and Carr amps were:

 

Telefunken --- Mullard --- JJ ECC83 --- Electro Harmonix 12AX7EH (the EH is currently in tests itself). The Groove Tubes supplied Chinese 12AX7C was also a hit, and for some reason had a different sound than the supposedly same Chinese 12AX7Cs from other sources. This is also being investigated.

 

The poor quality "chart" of the results can be viewed by this link:

 

http://guitaramplifierblueprinting.com/sovtek12ax7lp.jpg

 

Regards,

[saucyjack]

Myles,

what do you think/have you tested of the Ei 12Ax tubes?..a good set sure sounds good in my Tophat...And I've heard some Vox users swear by them

[myles_rose]

Originally posted by saucyjack:

Myles,

what do you think/have you tested of the Ei 12Ax tubes?..a good set sure sounds good in my Tophat...And I've heard some Vox users swear by them

saucyjack ...

 

The basic problem with the E! tubes is that they are very inconsistant. They either sound great, or are very microphonic. Out of every 20 we test, over half are too microphonic to use, or have some other problem such as the curves and specs are nowhere close to industry standard.

 

Having said that though, when you get a good one, its typically very good. Its hard to also look at them in regard to amps such as yours, as if they came with your amp, the folks over there probably went through a lot of them to assure that they would sound good.

 

All I can really say, is that if they are sounding good now, then they will probably sound good for a very long time. The E! tubes don't change over time ... if they are good, they seem to stay good.

 

As far as in a Vox, I would consider their preamp tubes, but would not use their EL-84 offerings unless I could match a quad really close first.

 

Regards,

[chairking]

A valuable post, Myles, thanks a lot. I recently

bought a Dr. Z amp (Z28) that has an EF86 preamp

tube and a 5751 phase inverter. The EF86 I replaced with a nos Mullard with good result. The 5751 is a Sovtek which I've read is like the 12AX7LPS with less gain. I know little about 5751s or phase inverters but

I was thinking seriously of replacing it with a nos tube. GEs are available....any thoughts on this tube and phase inverters in general? Thanks in advance.

Andy

[myles_rose]

Originally posted by chairking:

A valuable post, Myles, thanks a lot. I recently

bought a Dr. Z amp (Z28) that has an EF86 preamp

tube and a 5751 phase inverter. The EF86 I replaced with a nos Mullard with good result. The 5751 is a Sovtek which I've read is like the 12AX7LPS with less gain. I know little about 5751s or phase inverters but

I was thinking seriously of replacing it with a nos tube. GEs are available....any thoughts on this tube and phase inverters in general? Thanks in advance.

Andy

chairking....

 

The EF86 is a really terrific tube. It was used more in the past, but is coming back into favor in some of the new amps. It is a pentode, rather than a dual triode, as the 12AX7 tube. At 250 volts of plate voltage, it will drive about 3 mA, vs. the 1.2 mA or so that a 12AX7 will supply. It also has A LOT of gain. The 12AX7's gain is about 100 .... the EF86 has a gain of 5000!

 

In the phase inverter position of Dr. A amps I prefer the 12AT7, as it gives a bit more headroom and these amps can start to distort pretty quickly.

 

The 5751's gain is really close to that of a 12AX7 as today's 12AX7's at times are not as close to the original curves as the NOS of the past. If you want to use a 5751, I prefer the NOS JAN tubes, that are still just a few dollars more than a current 12AX7.

 

One thing with Dr. Z amps I have found, is that if you use output tubes that are very closely matched, there is more of a difference than on most other amps, including Matchless or AC-30's. Try to find something that is within 3 mA or less as a match. The tubes from Bob at Eurotubes are generally within 1 mA, and if he knows what you are after, he will make sure they are this close.

 

If you want to go the Groove Tubes route, their tubes are also going to fall in this range.

 

If you are on the other side of "the pond", then the folks at Watford Valves in the UK are a great bunch.

 

For NOS stuff, try KCA or Tube World.

 

Hope this helped somwhat .... but when all is said and done, its going to be your ears you have to make happy.

 

Regards,

[chairking]

Thank you, Myles...I'll try a 12AT7 in the phase inverter spot. In all the sources you mention for NOS tubes I don't see Upscale Audio (in your neck of the woods) mentioned. Thats where I got my Mullard EF86s

as well as some nos 6V6s which all seem great. Am I missing something? I must say, as a 51 year old pro guitar player who is really interested in fine tube amps and good tone, your posts on tubes and stuff related is right in the pocket...invaluable and myth dispelling...thanks....by the way...what exactly does a phase inverter DO?

Andy in Nantucket

[myles_rose]

Originally posted by chairking:

Thank you, Myles...I'll try a 12AT7 in the phase inverter spot. In all the sources you mention for NOS tubes I don't see Upscale Audio (in your neck of the woods) mentioned. Thats where I got my Mullard EF86s

as well as some nos 6V6s which all seem great. Am I missing something? I must say, as a 51 year old pro guitar player who is really interested in fine tube amps and good tone, your posts on tubes and stuff related is right in the pocket...invaluable and myth dispelling...thanks....by the way...what exactly does a phase inverter DO?

Andy in Nantucket

Andy ....

 

There may be an Upscale Audio around here, there are so many places its hard to keep track.

 

I don't think you are missing anything ... NOS 6V6's are really the only option as these days there are not really any good newly manufactured ones.

 

The phase inverter is sometimes called the output driver, and it is the tube that drives the power tubes. In a push pull circuit, one half of the PI drives one side of a pair, and visa versa.

 

By the way, I am 52.

 

As far as Mass .... you've got great seafood there. Years ago I worked for Data General. I lived in Framingham. I currently have a boat in storage in Vinyard Haven Mass.

 

Maybe see you out there sometime.

 

Myles

[chairking]

Seafood we have in abundance...and the good stuff at that! Give me a holler if you're up this way...we'll eat some. Upscale Audio is one of the best places I've found for NOS mainly because their testing seems pretty good. http://upscaleaudio.com/ also they seem to have some good stuff. They are geared towards high end audio, though and its not easy for me to tell which tubes would work best in guitar amps. They also have a return policy (which is nice when you're dealing with $45 on up 12AX7s).

Andy

[myles_rose]

Originally posted by chairking:

Seafood we have in abundance...and the good stuff at that! Give me a holler if you're up this way...we'll eat some. Upscale Audio is one of the best places I've found for NOS mainly because their testing seems pretty good. http://upscaleaudio.com/ also they seem to have some good stuff. They are geared towards high end audio, though and its not easy for me to tell which tubes would work best in guitar amps. They also have a return policy (which is nice when you're dealing with $45 on up 12AX7s).

Andy

chairking...

 

Thanks for the Upscale Audio link. They look like a great vendor. I will look into them more in the next few weeks and perhaps add them to my website also.

 

I will let you know next time I am on that side of the country.

 

Myles