MiG-25 jet

EMP? It’s NP for the 6C33C-B Tube

3:05 pm

If you’re a serious audiophile with tube gear chances are you know the names Balanced Audio Technology or Lamm Industries.  Unlike so many other tube amplifier manufacturers, you won’t find KT88, 6550, or 300B output tubes in their amps.  Rather they designs their tube amps around the unusual but impressive 6C33C-B vacuum tube.

Image courtesy of fly.historicwings.com

Invented by the Russians, this tube was designed to be incredibly rugged. The glass is so thick one tube weighs nearly half a pound!  The intention was to make a tube that could withstand an EMP attack (Electromagnetic Pulse) and severe G-forces.  You might be asking yourself, why?  Well, the 6C33C-B tube was not originally intended for hifi amplifiers. It actually was used to regulate the power supply of the primary radio in the MIG-25 fighter jet.  See why it had to handle the G’s?

This was a Russian secret until 1976. The West only discovered this super tube when defecting Soviet pilot Viktor Belenko landed his MiG-25 in Hokkaido, Japan. Lieutenant Belenko was a pilot with the Soviet Air Defence Forces and his defection provided the West with its first close examination of a MiG-25.  How close?  The Japanese invited the USA to dismantle and study it piece by piece.  In fact Belenko had brought along with him the operation manual assuming an examination of the fighter jet would be done and to assist with testing that might be done.  After a few weeks the Japanese were courteous enough to offer the return of the jet to the USSR, in pieces – 30 crates worth of pieces!  Apparently they also invoiced the Soviets $40,000 for the packaging expenses, but it’s believed that that bill is still outstanding.

6C33C Power Supply
6C33C Power Supply

By the 1990’s the 6C33C-B tube found a home in only a few mainstream vacuum tube audio designs.  It’s high transconductance and current, along with very low impedence made it a great alternative to the commonly used power tubes.  Today it can be found in any amp circuit topology, from OTL (Output Transformer-Less), to Push-Push, to Single-Ended.

You can download the complete datasheet here.

Balanced Audio Technology REX II
Balanced Audio Technology REX II
Triode 6C33C SE Amp
Triode 6C33C SE Amp

7 Responses

  1. Turner Truitt
    Turner Truitt at |

    Very cool info. I have a couple of amps that use this tube. Jon, How can you tell when it is used up and should be replaced? ( It does have some green and brown stencils on the tube glass that might change colors??)

  2. michael gloggnitzer
    michael gloggnitzer at |

    we have a spart delta with 4 6c33c, the sound is great – thank you for the great information and pictures, regards

  3. Anatoliy
    Anatoliy at |

    Actually, Belenko got a new jet, but with old electronics. The plant was behind the schedule and installed on this particular machine an old, vacuum tube, electronics, that was considered then obsolete. “EMP safe” is propaganda only.
    A first, audiophiles in Japan used them properly, in OTL amps, as cathode followers loaded on common cathode unity gain stages. In such case their non-linearity and wide spread of parameters were non-issue. However, as soon as such gorgeously looking Zhabas (Russian for Toad) become popular, boutique “furniture designers” started offering them in tradition PP amps with transformers, and even in SE amps, where linearity matters! Thanks to 6S33S tubes and traitor Belenko, we can easily count audiophiles now who prefer look to sound quality. 😉

  4. Ck Sim
    Ck Sim at |

    I just buy a OTL Stereo Power amplifier that is using 6c33c tubs . Could not find and information on this consider old model tube amp . Do anyone know any information ?

    1. Sandra @ thetubestore
      Sandra @ thetubestore at |

      Hopefully one of our followers can point you in the right direction.

  5. Clark Thomas Duffy
    Clark Thomas Duffy at |

    Does anybody know if the 6S33S is a true replacement to the 6C33? Electrically and soncially?



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