Preamp Deal of the Century

Hi Rabelais. No... The 6n23ev and 6n32eb are a substitute for a 6922/6dj8.

Thanks Ecclectique. You're probably aware that Roger Modjeski uses the 6BQ7 as the driver for the Music Reference RM-200, and he has been quoted as saying that you can drop in a 6922 as a sub in that application. I want to preserve the finesse of the Supratek down the chain, so I'm looking for NOS in that driver position. I'm all too aware that substitutions are not necessarily transitive (i.e., sub a 6N23EV for 6922 and a 6922 for a 6BQ7 doesn't necessarily imply subing a 6N23EV for a 6BQ7, but ... ).

P.S. Finally got around to dropping in 6F6G's in place of the 1940's Sylvania 6L6GA's as regulators in the Supratek. It's too early to site differences, but certainly an excellent tube in that position.

Hi Rabelais. I have always been a fan of Roger Modjeski's progressive vacuum tube design, he has always been a pioneer in the audio industry. If memory serves, Modjeski was the first audio engineer to employ the 6dj8/6922 dual triode in an audio circuit and bring it to market. Infact...from it's inception, the 6922/6dj8 was never really designed for use in audio amplification as it was primarily used in early vacuum tubed computers.In those days, the 12ax7 and 12at7 dual triodes were the audio industry's standard tube, and they were employed for gain in line stages as well as phono stages.At the time...With the rapidly growing popularity of the extremely low output Moving Coil cartridges[typically below .5mv] It was quickly realized that the gain of the 12au7 family of tubes was inadequate for driving these cartridges without experiencing tube rush or noise. Roger was instrumental in implementing the higher gain of the 6922 family of tubes in audio circuits and almost every company in the high end industry followed suit and embraced the use of that tube. That said: I wasn't aware you could swap the 6bq7 driver for a 6922, as they are really quite different electrically. Unless he has configured the driver stage of the amplifier to use the tube in a cascaded type configuration or unity gain,then perhaps you could sub it[but why?] Do "NOT" try substituting a 6bq7 for the 6922 in your supratek as your just asking for trouble here!!! Trust me here.... even if it will amplify the signal, it will surely sound wrong. The same goes for any other amp or preamp employing a 6922 for amplifying the signal. Regarding the 6f6g's in the supratek.... if they are new right out of the box..... give em 20 to 30 hours of run in time to come into their own. The early 1940's Sylvania 6L6g's are very good regulators in the supratek [bottle shaped versions]and great sounding output tubes as well.

Hi Ecclectique--most interesting. Sometimes it seems like half of high fidelity audio can be attributed to half a dozen extremely impressive individuals. I was cued into the 6922/6BQ7 sub in Roger Modjeski's "Manufacturer's Comment" to the 2002 Stereophile review (http://www.stereophile.com/amplificationreviews/560/index8.html). The relevant context is this excerpt:

Through my research, I determined that the much-maligned Chinese 6550 was capable of the highest peak-cathode currents of any 6550 available, and about 1.5 times higher than the venerated Genelex KT88. Once the grid-leakage problem was solved through the driver design, it was full speed ahead with the Chinese tubes. Granted, I have to toss quite a few, but far fewer now that my driver circuit can tolerate grid leakage. As to rolling the driver tube, if you like the 6922 or its higher-current 6H30 version, go ahead, the circuit won't mind—though in this application I prefer the 6BQ7 for its ruggedness, less delicate grid, and higher current. Just be sure the DC is matched in the two sections, as it is directly coupled to the output grids. We want to keep the bias balance within 10% in the output tubes.

I take good note that a 6922/6BQ7 is *not* a general substitution.

There is something a little more interesting going on here. Pre-amps like the Supratek that use 6SN7s and 6L6s are fertile platforms to rolling; there is no question that NOS tubes elevate the performance. But the KT88 is a desert for rolling; there is the GEC/Genelex and Tung Sol 6550--which can put you back $1K+ for the quad--or about half a dozen current productions that are more similar than different (JJ, Electro-Harmonix, Svetlana, Sovtek, Shuguang, etc.). So Roger's approach somewhat anticipated--in philosophy, but not in implementation--that of the H-cat; i.e., superb reproduction occurs (some would say demands) exacting control of balance and phase. This minimizes left/right and time smear, and results in the correct delivery of those higher-order harmonics and slight time delays that differentiate middle-C on a cello, from that on a high-school violin, from that of a Stradivarius. This is not what we do explicitly when we roll NOS, but perhaps some would say that implicitly this is what is happening, and that this is what separates the WE's and GEC's from the Sovteks.

Hey Rabelais. A very appropriate analogy and very well said sir. Phase splitters are antiquated, inappropriate and should never even be considered part of the equation in the design of high resolution vacuum tubed circuits.