Lets Talk About Tubes (Preamplifier’s Side) Part One
Since many of high-end preamplifiers have a thermionic “heart”, a tube “heart”, it is rather wise to raise a couple of relevant matters about the 6H30Pi tube just for the start.… Then on our next article we will talk about 12Ax7 (most common of them all) preamplification tube and today available variations.
As with almost everything Hi-Fi, opinions diverge widely as to which tube (and corresponding implementation) works best for preamplification purposes. Among the many designers, a good number felt – and still feel – that the characteristics of the ECC88 / 6DJ8 and, especially, its more “ruggedized” version, the E88CC / 6922, match quite closely the ideal design parameters for this kind of application. Thus, over the years, the soviet designed 6922 (6H23Pi) and its variants, became quite ubiquitous.
All this until the beginning of the 90’s, when Viktor Khomenko (an American designer of Russian origin…) passed a BAT advertisement in Audio Epress magazine, which revealed for the first time to the American public the 6H30Pi, also called “supertube”.
Originally designed as an avionics tube, the 6H30Pi came lately to the west because of the secrecy surrounding soviet military research (its export was banned, well after the “perestroika”). And, contrary to the 6922, the 6H30Pi is only produced at the REFLECTOR factory in Saratov, Russia. Which means that tube rolling – as we know it – is almost excluded (more about this, later).
So, what’s all this fuss about it? Why has it been called the “tube of the future”? Well, primarily, because of its superior technical performance: The 6H30Pi is a kind of 6922 “on steroids”. Because of its exceptionally high transconductance (72 mA/V), it can substitute three to four 6922’s for the same gain, albeit with higher current demands both on B+ and heater supplies (0.8 vs. 0.3A). This is the main reason why these tubes are not interchangeable. Moreover, the 6H30Pi is extremely quiet and, having a very low plate (anode) resistance of just 200 Ohm, makes the use of a cathode follower, quite unnecessary. As a result, the circuit is simpler, the transparency enhanced and – as an added bonus – low output impedance is achieved, thus permitting the correct electrical mating of the preamplifier with virtually any power amp. A near ideal – technically at least – preamp tube, indeed!
Let’s now come to the icing of the cake. There are, actually, three variants of the 6H30Pi on offer:
- 6H30Pi – EB, 6H30Pi – EH and 6H30Pi – DR
Letters in suffixes, meaning:
E – long life
B – high reliability
D – extra long life
R – extra high reliability
EH is a suffix observed in all Electro Harmonix tubes. You should consider these as specially selected SOVTEK’s.
Now, have a look at the photo…Do the three versions seem the same to you? Wrong! Because the “real deal” lies in the middle and is an original NOS pre-1992 military tube, manufactured with much closer tolerances and superior sounding. Which means that, in a revealing system, and given the thoughtful implementation of the breed in the CT-5, you will be able to fine tune the final result, just like you tune a guitar chord to perfection. It seems like a small detail but, believe me, it is not…Just do not expect to hear the kind of difference that might exist, say, between an AMPEREX 6922 and a TELEFUNKEN variant of the same. Fortunately (or…unfortunately) all 6H30Pi’s come from the same “stable” and it shows.