Tube selection

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.