Tube question: any sonic difference in 6SN7 vs 6H30 vs 6H80 in the amp's signal position?

I lived there for 35 years, and never saw  those in the commercially available devices.

Yes. It was made exclusively for the military.

The 6C33C tube was unknown in the west until 1976 when  Viktor Belenko, a russian fighter pilot landed his Mig 25 (Foxbat) at an airport in Hakodate, Japan  to defect to the west.  Little was known about the Mig 25 at that time so it was disassembled for analysis by Japan and the US (interesting note George H.W. Bush was CIA director at the time). The disassembled aircraft was returned to the Russians about two months later in pieces.  Analysts were surprised that vacuum tubes were used in the Mig's avionics systems supposedly because of better thermal tolerance and for EMP hardening.  The 6C33 was used for the power supply for the Mig's radio system and was remarkable for its power handling capabilities.  The first audio amp using this tube was built by a Mr. Dakasue in 1977.  As noted above the Russians made  a ton of these tubes.  Unfortunately quality control was/is an issue and good ones are not that easy to find.

Don't forget the same tube 6C33C was used on Russian ICBMs guidance systems

The 6C33 was used for the power supply for the Mig's radio system and was remarkable for its power handling capabilities. The first audio amp using this tube was built by a Mr. Dakasue in 1977.

The first American design to use this tube was the Atma-Sphere Novacron. IME the tubes stand a good chance of outlasting the tube sockets, which never specced for the kind of filament current seen with the 6C33. That tube was a modified version of the Sylvania 3C33 which was a dual power triode.  The Russian spec sheet calls for a 750 hour life; at which time the socket was expected to be replaced with the power tube. With such a short life and with a military application, this easily explains why so many were built (although in practice they can last much longer than that).


The sockets should be replaced about every 3000 hours or so. The filament connections overheat and loosen up. It is possible to re-tighten them once, but after that they will become problematic with the tubes not lighting up.  IIRC correctly they were made by the Uljanov plant, which was torn down about 20 years ago.

True, the first amp using the tubes was your Novacron Ralph