CRT Question - Old Calculator

There are many, although I cna't find any with the US-style numbers. Apart from the HR1 (another HV rectivier, on a B7G base), there are US subminiatures like the CK505 (pentode), CK509 (tirode), CK510 (tetorde), CK512 (pentode), M54 (tetrode), M64 (tetorde), M74 (pentode) and UK subminiatures like the DF66 (pentode), XFW10, XFW20 (both pentodes), DF70 (anotehr pentode), etc. Sure. The tabels I have say that '7' means 6.3V heater o na loctal base, etc. It's just another exception to the rule that the first digit(s) give the heater/filament voltage. IT's not strictly an American number, I think, but it's the right format : 2D21. That's what I know as an EN91, a xenon-filled tetrode thyratron. B7G base and 6.3V heater (of course) Also watch for UK Mazda (ntohign to do wit hthe car company) valves. These have a similar format number 9digits, letters, digits) but the code is totally different. The first digits do give the heater voltage -- except that 10,20,30 mean for use in series strings of 100,200,300mA. The lettes do give some info about the electrode stucture -- C = frequency changer, D = diode, F = pentode, L = triode, P = output penotode, etc. Yes, but the numbering scheme seems to have been designed nto to give useful information I always liked the term 'kinkless trtrode' for these :-). Over here there waa famous series of GEC output valves, much loved by Audio fanatics called KTxx (KT66 and KT88 being the most common). OF course 'KT' == 'Kinkless Tetrode' The name comes from the fact that hte beam forming plates etc supress the econdary emision from the anode, so the IA-VA curve doe not have the negative resistanve part that is forund in the curve of a plain tetrode. Yes, but there often _is_ a reason for the opcodes, if you search for it. For example, in the hP98x0 procesosr, the memory refernce instructions have the opcode in bits 11...14 of the instruction word. A simialr set of register-reffernce isntrcutions has the opcode in bits 7...4 and the opcodoes are essentially the same. It makes sense. In the microcode, the instruction word (in the Q register) is shfited to get the opcode bits in the same location, so the same microcode fork cna be used to decode the instruction. Of coruse there is no rrason why opcode 000x is load, 001x is compae, etc. You could reassign those with trivial changes to the mocrdoe. Bu that's like sayign there is no logical reason why 'C' in the Philips valve code means triode, 'N' means thyratron, 'L' means output tetrode/pentode, etc. That si arbitrary. But almost all valves coded that way use the same meaning got hte letters. So if you can rememebr the 20-or-so letters adn teir menaings you can figure out what any such valve is. So that, for exmaple, if soembody tells you their radio has a UABC80 in it, you can deduce from the fact athat the 'U' means 100mAheater, it's likely to be a series-string AC/DC set and from the fact taht it's a trible diode (AB) and triode in the same envelope that it's likely to be an AM/FM set (AM detecotr, FM discriminator, and first audio amplfiier). -tony