"OTK" stamp on russian devices
I would like to start a thread about these quality control numbers, to gain wisdom and share it with anybody interested.
So far I was unable to find any relevant documentation on the subject, so I'm asking for help.
These numbers are particularly interesting, because we all know that some russian tubes have very wide tolerances, and the quality can also vary singnificantly from one device to other.
So, gentlemen, let's put it together !
Jan Wuesten, who sells all sorts of interesting things (Jan's English Site) posted this in the neonixie-l forum of Yahoo!!!:
"OTK" has been variously described as a "state technical bureau" mark or "military controlled" inspection mark. IMHO in many cases now it is almost meaningless, and is roughly equivalent to "inspected by" with the number following being that of the specific inspector or inspection process. (Variously described.) It's really hard to get straight answers.
I have had many Russian tubes with the OTK mark on them, some have been quite good, some have been less so. Production quotas being what they were in the Soviet Union era I suspect that towards the end of each month a lot of very marginal tubes got the mark that might not have otherwise made it through.
The Soviet military probably skimmed the cream of the crop and the less desirable ones went into the domestic/export market.
Older tubes with these marks have generally been good, and I suspect are often ex military stock. More recent ones can be very questionable. I still see the OTK mark on current production tubes from Svetlana (Winged C) and others that are clearly not destined for military use so I question whether the mark has any meaning today. Many of the tubes in question failed spectacularly operating well within their design margins. (SV300B and earlier versions of the 6550.)
A long ago friend who served in the Red Army noted that it was usual to retest tubes prior to installation to make sure that they met their specs. He mentioned some equipment would go through burn in for a few days just to make sure. Probably SOP for most military services regardless.
Your best bet for good Russian tubes these days at least in the USA is one of Mike Mathews/New Sensor's various captive brands. (Sovtek, Tungsol, Mullard, EH, etc.. ) These have generally been very reliable and any problem tubes replaced without question. For the moment at least he still owns/controls the factory they are made in..
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