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Brain,

C’mon, I was kidding about the “Electron Intensification Interface”! There is nothing in this phonocorrector then a correct selection of tubes, thier proper (well almost proper) use and selection of the specific topological decisions that sold-like produce more “interesting” result.

If you lined up the same valve types than I may share with you some usability options that you might find useful.

The 7721 is a spectacular output tube in this application. Probably the mostly available are Siemens-made 3DA in Rohre boxes and they are one of the best sounding 7721 as well. The old Siemens 7721 (in none Rohre boxes and with small Siemens printing) was actually made by Telefunken and you will find that in many instances the Telefunken tubes will be sitting inside the Siemens boxes and wise versa. The constriction is very much identical and they sound indistinguishable. Although the old Siemens/Telefunken tubes look sexy and hard to get but I do not detect that they sound more interesting then the Rohre-Siemens (I call them New Siemens but only because the Rohre boxes looks are colored and look fresher. In fact, the Rohre-Siemens tubes are 40 years old as well or something like this…)

With 7788/ E810F you have more variety and way more different result. Here are many 7788 out there. Here are some 7788 that I have tried:

1) RCA’s 7788 – kind of strange tube. It sounds abrasive and mean, sometime even rough.
2) Mallard’s 7788 – there are different versions of them, different printings but they all have similar constriction. Mallard 7788 have the strongest among any other tubes bass, sometime is unbearably strong. It has slightly rolled off the HF and some kind of notchy midrange. When I was listing the Mallard 7788 (and I have a half dozen of them to select from) I fell that I am at CES show staying at the door of someone’s room…However, the Mallard 7788 are dead quiet.
3) Philips’ 7788 – they are OK but the do not have that sense of nobility and lush that the best 7788 have. It is possible that the Philips that I trued should be burned longer…
4) Amperex 7788 – very good tubes with practically no microphoniks. The USA PQ production with yellow printing still might have some VERY minute noise but the Holland production with white bold printing (Premium Quality) are insultingly quiet. You can actually tap the operating tubes with volume all the way up and you might not hear anything from loudspeakers. Sonically the Amperex 7788 are excellent, US or Holland made, and if you used then they you might not need even to shock-mount them.
5) Siemens/Telefunken 7788 – they are the same production as well. They are also are fantastically sounding 7788. I for a while felt that Siemens/Telefunken 7788 have no advantages over Amperex 7788 but very recently I took a pair of Telefunken 7788 and burned-in it with a signal for on my other phonocorrector. As the result I found that I prefer the Telefunken 7788 to Amperex. Well-burned Telefunken has less zippy and hi-fiish HF and more fascinating mid-range, way way way way more fascinating! The Siemens/Telefunken 7788 are more microphonik then any others :-( and it will require some precautions to use them. However, it dose worth it.
6) DuMont 7788 – very good tube but it dose not let it go… It is slightly uptight and tense; perhaps I need to let them to burn longer….
7) G.E.C – very strange tubes. Despite of reputation they were probably the worst that I heard. However, I have juts one pair of them and they were used. Perhaps I have existed pair of them. In my tester they do look quite weak…
8) I have a few more 7788 made by no-big name manufacturers: Penniack, Gollo and so on but they do not sound well-enough to memories the manufacturers names…

I hope you find my little run over those high transconductance tubes useful. I currently run Telefunken 7788 in front. It sits in amortization sockets and wrapped into a grounded cupper jacket. The socket in mounted within the ¼ Teflon board. The board sits on the wooden stand-offs inside 4mm still box. The box is loaded with lead shots sealed in epoxy bath. With all those precautions the noise-wise it is quite phenomenal even with high-microphonik Telefunken tubes. In order to begin to hear any HF nose from my horn I need to add 18dB to my preamp to my normal listening level.  There is no LF or any another noises. BTW, even when I add 18dB on my preamp stick my head onto the horn and listen the hiss then the Telefunken has the more pleasant and none-annoying hiss among all, probably with a very close following by the Amperex…

Rgs,
The Cat

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