Beautifully implemented Enigma-man! I particularly like the use of smaller displays for the annunciators. And my type of 'fun' engineering too.
Yes, all the pre 106x Datrons used socketed Sperry / Beckman / Babcock/ SP3xx displays. The mV / V etc annunciators were done with dim lamps behind transparencies. They are also a 'micro free', no batteries, no eproms, just discrete analogue and socketed logic, making it possible to maintain them more or less indefinitely. They still achieve 0.01% class accuracy and stable 1uV resolution. Well worth grabbing if you see one cheap (avoid the 105x 5 1/2 digit series, it uses an unobtainium custom PMOS counter logic chip and a very touchy triple slope conversion circuit).
I think it was sad that adopted a custom panaplex display on the later models, but every major manufacturer did the same, but it is a definite weakness when it comes to restoring older units. Remember though that a lot of the 106x meters on the market have been left on 24/7 for decades.
@bitseeker:
What's the sepia-colored staining on the PCB?
No idea, it's on the surface and definitely not heat related, my guess is either flux residue or lacquer. It's not sticky and I've never tried removing it. BTW did you notice the big beehive trimmer cap up next to the glass encapsulated crystal in the top right corner? That's the frequency trim.
I really like the look of the Panaplex displays, but don't have any yet. What's a reasonable expectation for lifetime? I've seen others with, for example, Datron equipment and the displays have gone bad. Are they better, worse, same as VFD?
Life is certainly
way better than VFD - particularly due to absence of uneven brightness loss. The Sperry / Beckman spec states a blanket 10 years with a note that operating at Maximum rather than Typical ratings can reduce life. In practice it's difficult to get them dim enough, even at Minimum specified current (They were specified at 200ft lamberts (
) and a viewing distance of 40ft). I suspect that minimum current drive increases their life even further. Like all cold cathode tubes, the cathodes will splutter if overdriven.
As you say Cubdriver, they are more mechanically sensitive than anything, the front glass is bonded as are the pins, but I think they use glass 'frit' seal (as cerdip packages). There are also internal getters (the little ring structure at the bottom) to mop up gasses. Given that many of the ones still in use are 40+ years old, long term leakage doesn't seem to be an issue.
@Arhammon: Yes the Philips one is particularly nice, it's a multiplexed display (multiplexing does seem to look better, maybe because it drops the brightness below what can be achieved at minimum current in static drive). It looks a lot nicer than the LEDs they used on later counters.
P.S. I should probably qualify that multiplexed display comment. What sets the minimum current spec of the display is having sufficient current density to light up the entire surface of a segment. When multiplexed, the segments get driven at higher current, but for lower duty cycle. This seems to make them look dimmer and 'sharper'.