I'm in the process of getting some A2B neons from Mouser. Dave
-----Original Message----- From: volt-nuts [mailto:[email protected]] On Behalf Of Charles Steinmetz Sent: 18 November 2017 13:11 To: [email protected] Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper David wrote: > Then an A3C (NE-2U) shouldn't work. The drive voltage is 125V. Correct. > The operating current is 1.5mA (.15V/102R) in the 3420B, so I would expect > this to be the A2B (NE-2V) part. The NE-2V is another 700uA design current lamp, just like the CML A2B and A2B-T. Indeed, if you look at p.117 of the 1965 GE glow lamp manual I linked to yesterday, you will see that it lists the NE-2V as an "A2B" lamp, with "NE-2V" in parentheses. So, the primary designation for this lamp was "A2B" at least as far back as the mid-'60s. Note that 700uA is the "design current," not the maximum safe current. GE explicitly sanctioned using neon glow lamps at up to 2x the design current, and they were routinely used at even higher currents back in the day. Some of GE's published application circuits used them at 2-3mA. Mostly, the design current was the current at which the lifetime was rated (higher current leads to shorter life). It seems easy enough for you to obtain CML A2B or A2B-T lamps from either Mouser or Digi-Key in the UK, so why don't you just get some and see how they work? > Interestingly the operating current for the 3420A is 2.45mA which you would > think might suggest the A3C (NE-2U), but the drive voltage isn't high enough! I would not be surprised to find that the original neon lamps in the 3420A were 700uA "design current" parts that HP determined had sufficient lifetime at the 3420A operating current. If this is correct, presumably the 3420A choppers fail with lower operating hours than the 419 and 3420B choppers. (Perhaps this is why HP reduced the neon currents in the "B" version?) Note that 700uA was the highest "design current" rating for wire-leaded, standard-brightness neons back in the day. In a related vein, neon glow lamps produce less light as they age (both from envelope darkening and because less of the cathode [DC operation] is illuminated). This may mean that the HP optical choppers degrade significantly before they outright fail, so the chopper amps may start drifting more than specified some time before the choppers fail entirely. Best regards, Charles _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
