Jamie, I have had exactly this problem with these B5750 tubes! I'm glad it's not just me. I've had 7 open circuit, I had 4 shorted to another digit, I had another tube with a resistance between two digits - not a full short! These were also on boards that had a lot of hours on them and looked a little physically beaten up. Out of 8 tubes, 4 had faults. These were on two boards multiplexed with a wierd DTL decoder (with inverted binary) and 1960s pcb.
Cheers, Andrew On Sunday, February 12, 2023 at 10:14:50 PM UTC James Montgomerie wrote: > Hey folks, > > Been lurking for years, but just joined properly now. I designed and made > a clock myself a few years ago, using Burroughs B5750s on ‘original’ > vintage carrier cards (pics attached, though I don’t think they’re > important to the question I have). The clocks have been working for a year > or two (and the pictures show them when they were working), but they have > started to fail in a way that surprises me. > > The anode resistors burn out and (unsurprisingly) the displays stop > working. Analyzing at the components after a failure, the thing that sticks > out to me is that the tubes themselves seem to have shorts in them. In one > case, the ‘0’ has shorted to the anode. In another case the ‘4’ has shorted > to the anode. Given this I think what must be happening is that the tubes > develop these shorts, this causes too much current to be drawn when these > numbers are meant to be illuminated, and in turn this causes the anode > resistor to burn out. > > Sometimes, before the failure, multiple numbers light at once, and/or the > front of the tubes get silvered, but I’m not sure this is related. I think > the multiple-numbers-at-once might be being caused by the ground-side > control circuitry having to sink too much current from the short. > > The repair is easy - replace the tube and anode resistor, but I’d like to > understand the problem better and perhaps prevent it. > > The power supplies seem fine, and both the supply voltage and the voltage > across the anode resistor (and, by implication, current - about 2.6mA) are > good when the tube and resistor are replaced. > > Is a dead short internal to the tube a common fault I should be preparing > for? Could it be caused by power surges or the like (in at least one case, > the clock seemed to fail immediately after a power cut)? Is it likely that > something in my circuit design could be is causing or encouraging this? > > Thanks for any help! > Jamie. > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/b0d911f2-a737-489f-a56c-e986edf91023n%40googlegroups.com.
