Tube selection

I am currently using Sovtek 12AX7WXT tubes in my preamp and CD player output stage. I like the full rich bass and midrange of the tubes but I feel the highs are lacking in air and frequency extension. I have tried the Mullard and Telefunken equivalents. The highs with respect to both of these tubes were superior to that of the Sovtek but the mids and bass of both tubes were much thinner than the Sovteks. Any suggestions with regards to any available tubes that combine the bass and mids of the Sovtek with the highs of the Mullard and Telefunken? Any help would be greatly appreciated.


The Sovtek does have good bass. The Telefunken should provide equal or better, in addition to the improved highs you are already aware of. There is always the possibility that your units were designed around the Sovtek and both of them prefer the physical and electrical properties of same. The Sovtek is the only current production 12AX7 that is (IMO) really good.

The NOS tubes you mention will not react the same in every circuit, and unfortunately only trial and error will determine the best result. You should first be certain that the NOS tubes you are testing are not already worn out, and that they are free of microphonics. The other tube that has great bass is the Siemens CCa, and it too will react differently in different circuits. If in the end you find that the result with the NOS tubes are not what you want, just be happy with the Sovtek, it is indeed a bargain in today's tube market where the Telefunken and Siemens often command $50.00 and more per tube.
Albertporter makes a good point. I have a Siemans 12ax7 in combination with 12au7s made by Amperex in my Anthem amp. I like this combo,but on the flip side the Bugle Boys in my dac(sonicfrontiers) sounded soft compared the the Sovteks I replaced them with. Then again the BB's probably had some age on them.(they are used) Good listening!
I replaced Sovtek 12AX7's with Telefunkens.These go in the first 2 positions of my Rogue 99 phono stage.The Tels are much quieter and offer better bass,highs and more liquid mids.The price sure is much higher than the Sovteks but the sovteks have been known to have a short life span.The Tels are good for 10-100,000 hours.Sounds like a bargain to me!
As a designer of Professional Broadcast Audio Equipment, I am surprised about the discussions about Tube Sound. The characteristics of individual Tubes and Transistors of the same type vary by a very considerable margin. In good design, it is not good practise to rely on the specified characteristics of a particular active component such as for example a Tube. Instead, the design should allow for wide variations in gain, and be arranged to compensate for this. I have recently designed a Professional Valve Power Amplifier for serious Monitoring using ECC82/12AU7 in the driver circuitry. The design use generous Cathode Degeneration. Ie. what is known in solid state Amplifiers as nested or local feedback. Testing about 25 ECC82/12AU7 Tubes of various makes and ages, some used, I found no significant differences in overall performance of the amplifier, no doubt thanks to the way the Tubes were applied. An Amplifier relying on precise performance characteristics of Tubes or Transistors for that matter is badly designed. The Professonal Amplifier mentioned use either KT88 or 6550 Tubes in its output stages. There is practically no measured difference in performance between KT88 and 6550 Tubes except for overload behaviour. As expected, the 6550 Tubes produce marginally more power and overload more abruptly than the KT88 with the KT88's sonicly being more pleasant because of their softer overload behaviour. This is understandable and as expected considering Beam tetrodes versus Pentodes. I can see no reason for differences in sound quality between healthy Tubes used in low level stages other than poor or bad design of the circuitry in the first place.
Who wants to tell Capt. Kirk we're not talking measurements, here?
Beam tetrode aboard Capt Kirk!

Damn it Kitch, I'm an audiophile not an engineer, but I'll try to coax a few more electrons from the Telefunkens before the Klingons are removed from Uranus.
I can relate to Albert's post regarding the low end capabilities of the Sovteks. I recently upgraded from a Modulus 3 to a 3a and have been listening with the Sovtek 6922's before dropping in my Siemens 6DJ8's. While they are not as smooth or cleanly detailed as the Siemens, the bass is just outstanding -- things are not broken in yet so sound may improve a bit more. Have things changed with Sovtek over the past few years? As I recall, the Sovteks that were in my Mod3 in 1993 didn't do anything right.

So far as 12AX7's are concerned, I just picked up some of the Mazda chrome plates from 1963 vintage for the imputs on my amp. This is a very nice tube all the way around. A good balance of smoothness, detail and extension. You may want to consider these as a more lively alternative to Teles and Mullards which might strike the balance you seek. Good luck.
Ouch, Albert! Even at warp speed, us over 50's could never pass a Klingon.
On the recommendation of Leafs, I bought Amperex 12ax7 from Andy at Vintage Tube Services. His choice for a little more top end than the Mullards or Telefunkens. They do sparkle a bit and don't give up anything in the bass. Very balanced.Steve, you should give them a try. Tested as lightly used, they were about $40 each and sound great.
Poulkirk: What properly designed amps do you recommend that cut it on music? I have been stumbling about at this hobby for 35 years and have not tripped over one yet that will not benefit from the the "right/specific" tube for the right application. My amp is so lame that I switch out the input tube 2 to 3 times a day, depending on my fancy.
Dekay, you leave me SO green with envy! Tubes AND Time! (Yes, it has its price, but still...)
Dekay. We are based in Australia, so it is probably not practical to recommend our Tube Amp. I will be happy to email you some details on it in PDF format if you provide me with your email address. I can show you the basic Amplifier Circuit, No Component Values, a picture and the specs. Thereis also a little bit about it on our web page,
Poulkirk: I am not a technical person, but thanks for the offer. I will however take a look at your website. I did not realize that you are a manufacturer and that we are talking about your own design and apologize for being a bit snide. Are you looking into representation in the states? Also, are you saying that different (or NOS tubes) do not change the sound of this amplifier? If so, then this has its pros and cons as although we all gripe about the cost of NOS tubes, I believe that most of us enjoy the flexibility that they offer as the sound can be tailored at ones whimsy (granted that one has the tubes to do so). There is however a very popular preamp (Audible Illusions) that can only accept a few brands of tubes as it runs them very hard and most will not survive very long in this circuit. This has not hindered the units sales as far as I know as it is a good sounding product as is. I don't give up very easily though and just picked up a pair of Siemems 7dj8's for a friend to use in his in place of Soviet 6922's in the hopes that it will give him a change of pace/sound.