Saratov (Sovtek) KT66s

[Casher O'Neill]

Since the Dynaco ST-70 manual states you can use a KT66 instead of the EL34s, could you also use a 6L6GC? If so, what changes would you have to make? I know that one good thing is that the heaters for the 6L6 draw much less current.

[EWBrown]

6L6GCs should work, just check the biasing. As long as the pinouts are compatible and the voltage ratings aren't exceeded, just about any tube in the 6L6/6CA7/EL34/KT66 family should work fine in an ST-70. Some of these tubes like to work into a 6600 ohm primary OPT, but will still work fine into 4300 ohms without any serious issues.
The ST70 has pins 1 and 8 tied together, in some of these tubes, the 3rd grid may go to 1, in some others it may go to the cathode (8) directly.

I just finished a new build ST70 using an old ST70 carcass, two NOS OPTs from E-bay, Triode Electronics' power trannie and C354 choke, and tubes4hifi.com's VTA ST70 driver board. Works and sounds great!

The VTA driver board uses three 12AT7s, as a triode voltage amplifier and long tail pair phase splitter for each channel, very similar in circuit design to that used on the EIclone (or some VTL amps). The GZ34 and 12AT7s are JJs, the EL34s are Svetlanas "S" labelled tubes, not the newer "winged C" versions currently available. I am planning to try out some Saratov KT66s and some NOS US made 6CA7s I have ben saving for many years.

/ed B in NH