Eico 950B Voltages low no eye tube screen glow.

[SwizzyMan]

Hello all!

Yesterday I was testing a filter cap with my recently acquired Eico 950B. As I was lowering the voltage to discharge the cap I heard a pop and the screen on the eye tube flickered out. But, the filament on the eye tube is still glowing. I am now getting only 367 volts at the 500V range on the voltage dial and the eye tube screen still will not display anything. I am not sure what I did to make this happen. I made sure I was at the correct value, I was. Could this be a cap/resistor issue? Or an eye tube issue (note that the eye tube filament glows but no green screen).

[WISCOJIM]

Vintage test equipment, just like old radios and TVs, needs to be serviced just the same. Check caps, resistors, etc. and replace all out-of-tolerance parts first and troubleshoot what is left.

[Zenith26kc20]

Mine did that. I changed the eye tube (1629?). I don't bleed the caps off anymore with the unit. I use a large, 10 watt 470 ohm to do it when I finish checking the cap.

[SwizzyMan]

Originally Posted by Zenith26kc20

Mine did that. I changed the eye tube (1629?). I don't bleed the caps off anymore with the unit. I use a large, 10 watt 470 ohm to do it when I finish checking the cap.

Well I am getting some off value resistors. Should I buy a new eye still?

[Olorin67]

not sure about that unit, but many cap testers use a split power supply, because an eye tube cant handle 500 volts on the plate. The eye tube is across one side of the power supply. since your voltage is low, maybe the side that feeds the tube has an issue, bad cap or something.

[Tubejunke]

Yeah, my older (tan) C3 Heathkit did the same thing. I had just got it and it worked for a few power ups and then a sharp pop and nothing. I never bothered checking the DC outputs. No eye and the unit is NO good, so I just popped in two 10mfd 500VDC power supply filter caps and everything came back. The outputs aren't dead on face value, but they are in the ballpark. Drifted resistors likely cause that I imagine. I have another where all outputs are low and the resistors check out. I'm figuring a cap I haven't replaced maybe. I've only been messing with old cap testers for about a year. I never wanted to repair my repair equipment in the past. I most often do more work with VTVMs and cap testers than I do radio or tv. Something different is nice.

[jr_tech]

This site has a pretty good discussion (and partial schematic) of the 950B... bad power supply caps or changes of resistor values in the voltage divider can mess up the voltage to the eye tube and the leakage test circuit.

http://tubesound.com/2008/08/23/rc-testers/

not affiliated,
jr