Tube Selection For Shannons Driver Board?

[hilldweller]

Hello Everbody, I'm A Newby Here And I Would Like Get An Idea For What Works Well With This Driver Board. I Currently Have Some Sovtek 12AX7LPS And Some JAN 5814A As Well As Some Sovtek 12AX7WA Lying Around Collecting Dust. I Would Appreciate Any Of You Experienced Members Advice. I Am Not New To Tube Audio Equipment But I Am New To The St 70 As I Have Finally Won A Decent One On Ebay And Want To Make It Sound Superb. I Listen To Classic Rock And Classic Jazz Music And I Like It Loud And Clear. I Am Looking Forward To This ST 70 Project And Would Like To Share It With The Forum. Yellow_Light_Colorz_PDT_12

[kheper]

This tube preference/rolling mumbo-jumbo
is very subjective. I like NOS Tung-Sol
and NOS RCA 'clear-tops' for the 12AU7s.
And, NOS RCA 'whatevers' for the 12AX7
tube, because they are far cheaper than
Telefunken.

One tube, in my opinion, to avoid is
new production JJ 12AU7/ECC 83 tubes.
There are rather noisy and they seem to
mask the detail in the music. The new
production JJ 12AX7s are not too bad,
but you could do better.

[EWBrown]

Any kind of 12AX7, ECC83 or 5751 should work fine for the voltage amplifier (the middle tube) and any of the 12AU7 derivations, 5814, 5963, 6189, ECC81,etc should work and sound good. 12BH7s should also work weoo, though they may require a minor plate resistor value tweak to get the full benefits.
All of these are direct plug-in compatible. A lottle etch surgery, then 6CG7 / 6FQ7 and 6GU7s (filament pins 4 and 5 only) can be used in place of teh 12AU7s.

"Premuim" 12AX7s and 12AU7s can be costly, but here's a little trick...

Look for Heathkit Color TV dot & bar generators, the later tubed version contained Mullard 12AT7s and 12AU7s. I don't recall the exact model number, but you want the one with the heavier power trannie, and which contains 13 ttubes. Six of these are generally Mullard 12AT7s, and 3 are Mullard 12AU7s. (It helps to bring a screwdriver, or at least a flashlight so you can peek inside through the vent holes). Similarly, Mullard and Telefunken 12AX7s can be found in some of the late 50s, early 60s vintage mono AM/FM tuners, which can be found fairly cheaply.

12AT7s won't work properly in the ST70 driver board, without some resistor changes, but they are very useful as the driver stage in 2A3 and 300B SET designs.

HTH

/ed B in NH