CRT Question - Old Calculator

Here's another follow-up on the HV supply for the CRT in the Wyle Laboratories Scientific WS-02 electronic calculator. I found some screws (hidden behind other stuff that had to be removed) that secure a perforated metal shroud around the high voltage power supply. It was a bit tedious to reach some of the screws, but I was able to get them all removed, and take the shroud off. Once the shroud was out of the way, I found a small circuit board with two vacuum tubes plugged into it, and a number of other components, as well as a transformer of some type, but definitely not a flyback. I suspect that the tubes and circuitry on the small circuit board are an oscillator that is used to pump the transformer to generate the high voltage that goes to the CRT. Given this discovery, it added more confidence that it will be OK to power the thing up without causing any damage. I pulled out one of the tubes. It is a mini-style tube made by RCA. However, it has no part numbering on it at all. It has 8 pins, and given its application, it's probably a simple triode. The other tube is difficult to get out without disassembling more, so I'm not going to mess with it. I do hope, though, that these tubes are good, as getting replacements could be difficult if either or both are not good. I put DVMs on the +12, -12, and -30V supplies so they could all be monitored at once, and also put a 'scope on the same lines so that I could look for ripple riding on the DC voltages. With a variac, I very slowly (over the course of about 20 minutes) ramped up the mains voltage in 10% increments. The power supply voltages came up slowly, in a pretty linear fashion as the mains voltage was increased. At 70%, the +12 and -12V supplies had stabilized, at +12.03 and -12.06 volts. At 80%, the -30V supply had stabilized at -29.90 volts. When I went to 100%, I could clearly see the heaters glowing (with the room darkened) in the two tubes in the HV oscillator. I don't have a high voltage probe, so I didn't try testing the HV supply to see what it was running at. I definitely don't want to get zapped by trying to use normal probes to check this. The ripple on the main power supplies was surprisingly low. There was about 3.5mV of ripple on the +12 supply, 3.2mV on the -12, and about 4.8mV on the -30V supply. I think that these are likely well within acceptable levels for normal operation of the machine. I also kept a close eye on the capacitors in the power supply, and there was no sign at all of any kind of heating or leakage of the caps. I let the thing run for about 20 minutes, keeping an eye on everything the whole time, and everything stayed stable. The next step will be to put some load on the supplies and see if they hold steady. This is a really cool early electronic calculator, and it'd be phenomenal if it were to be able to run again. The fact that the power supply seems to be in good shape is a great first step. Thanks again to everyone for their input on this. Also, thanks to Al Kossow for putting the documentation for the machine online on bitsavers.org. If I do have to dig into the machine's logic, this information will be extremely helpful. Rick Bensene The Old Calculator Museum http://oldcalculatormuseum.com