6C33C tubes - sonics, implementation & availability

We were the first company in the US to use that tube (in our Novacron amplifier, about 1991).

You are correct- the tube stopped production about 1999 when the plant making it went offline and was torn down. There do seem to be large numbers of them available though.

We used them in an OTL as that is what we make- the tube itself is good at this task, being capable of high current, good linearity and operating at a low plate (B+) voltage. Its primary weakness is that it was designed for an American Septar tube socket that is overloaded by the filament circuit of the tube. For this reason it eats tube sockets. The best sockets we have found for the tube so far are ceramic.

The sheet metal has to be designed to allow the socket to cool properly. If this is not done the socket will have a very short life (and possibly the associated wiring as well); less then 1000 hours. Longer life comes with proper design but in all cases eventual socket replacement will be required.

Its tricky to compare it to a tube like the 300b due to the fact that the output transformer is an enormous variable in tube operation- and in particular single-ended operation. I would say it sounds every bit as good (we built an OTL using 300bs as well) but its a lot trickier to build an OPT (OutPut Transformer) for it due to the lower plate voltages, higher plate currents and the higher power levels. So actually auditioning the differences is tricky as well. However in our experience it has a very detailed, smooth and robust character.

Of course, we think that an OTL is the preferred embodiment; single-ended aficionados will tell you that single-ended is the way to go, and so on. So I would not worry about that bit of it. 

 

Thanks, Ralph, for your comprehensive comments!
Forgive me for not including the OTL topology used in your earlier offerings as well as Joule Electra, etc. I wish there was a way of knowing whether individual manufacturers use more heavy duty sockets and wiring. I’ve also read that warming the filament for 3-5 minutes before HT power is applied may prolong tube life.

There is no such thing as a 'heavy duty socket' for that tube!!

The typical warmup time is about 5 minutes.

We recently reissued the Novacron in an updated version.

Its a popular tube with OTL manufacturers. In fact most OTL manufacturers use it; you don't have to use very many to make power and it also has a low plate resistance.

Another good source for information is Vlad Bazelkov, maker of Audio Mirror amps that use that tube.  Great guy. 
http://audiomirror.com/

Excellent info here: "The 6C33C Survival Guide".  My 50w push/pull monoblocks use them.   No need for a space heater in the winter.   I’ve purchased many of these tubes from Russia via Ebay.   The sellers were always trustworthy.   Yet, some tubes were DOA.   I just purchased 50% more than I needed.

Here are photos of it being used in the guidance system of a Russian cruise missile.

^^ the survival guide is good with one exception; Romy's assessment of the Japanese socket is flat out mistaken! They actually have a shorter life than the ceramic sockets and should be avoided. This is because the 'plastic' he refers to is actually Teflon and is such a good insulator that the pins of the socket actually run much hotter than they do with the ceramic sockets. I have to assume that he never used them or he would know this.