So the V620 and V634 tested OK. My buddy wasn't able to test the V659, but it shouldn't be the main problem at this point anyway.
My plan is to next replace the V692 diode tube.
I still would like to know about my questions 1, 2, 4, and 5 below before I search for the diode tube though.
Thanks,
Ken
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--- In TekScopes@..., "whippletreefarms" wrote:
Thanks for all the input everyone. I got another DMM and an HV probe. My old meter did indeed start giving erroneous results. So here is where we stand now:
Normal situation (nothing removed and no wires lifted, measured with new meter)
-3kV rail = 0V
+500V rail = +260V to +270V
+250V rail = +150.4V
+85V rail = +97.8V
+100V rail = +60.1V
+12.6V rail = +4.97V
-100V rail = -57.2V
I know the HV probe is working, because I measured the +500V rail with it both before and after measuring the -3kV, and it corresponded to the direct measurement.
I'm guessing that my old scope somehow shorted the +500V to ground and that was the spark I initially saw. It hasn't repeated since, so this must have been a red herring.
I removed the -3KV rail from the end of the diode tube, and the voltage at the end of the tube still measured 0V.
Per Albert's comments:
* When removing both the V620 and V634, the +500V rail increases to +476V.
* With R628/C628 shorted to ground, the +500V rail reads +315V.
* The voltage decays to about +120V about 20 seconds after power off.
* The V659 is a 87V voltage regulator, so I would be surprised that it hasn't ignited by +97.8V.
Per David's comment:
* C611/C612 probably isn't an issue now that I am getting consistent (although incorrect) +500V readings.
* On a related note, however, they held voltage a LONG time after shutoff, so long in fact, that I had to actually remove the white/red T620 wire to measure the resistance!
Per Dan's comments:
* The V620 tube has an orange glow on a vertical element. I'm not sure if this is the same as the plate glow you mentioned. It does get hot - too hot to touch.
* See comments above on removing V620, and also measuring decay time
* -3kV to ground measures 4.7 MOhms to ground
* I removed the CRT filament (white/yellow wire, pin 14) from everything, and measured that it was open to ground.
* I measured the other CRT lines to ground, and they all seemed reasonable based on the circuit diagram.
I suppose it is possible I added to my woes by bunging up the V692 lead when lifting wires and thus causing 0V on the -3kV rail. Or maybe it has always been 0V, but since I couldn't measure before, I don't know.
So my new round of questions:
1. Is there a way to measure the input to V692? The power-off T620 measurements all seemed correct.
2. Does the +97V on the +85V rail indicate V659 is bad?
3. I plan to take V620, V634 and V659 to the hardware tech at work. He says he has two tube testers in his attic and can measure most tubes. Thank goodness for his "things were so much better in the old days" curmudgeonly attitude!
4. (tube circuit newbie question) A couple of you mentioned the "oscillator". Which tube is that? The V620 or the V634? And what frequency does it oscillate at?
5. What to try next? I will say I am learning an awful lot, and am not ready to give up yet!
Thanks again,
Ken
