Predicta 17" HV question

[Phil Nelson]

Thanks for the ideas. Here's what I found.

Bridge the 100 mfd cathode bypass.

Tried, no change.

Rotate v lin while measuring cathode, pin 9. It should go to 0 at extreme end.

If you mean going to zero volts, it never goes below about 20 volts. Resistance of the v lin pot varies from about 10 to 770 ohms. I wonder if this is a replacement? The manual calls for a 1500-ohm pot with a stop at 180 ohms. This looks like a (roughly) 750-ohm pot and someone added a 950-ohm/1W resistor in series to make a max of about 1700 ohms. So, with the resistor the pot is varying between about 960-1700 ohms. Shorting that resistor didn't change the height noticeably.

Bridge electrolytic on the 275 volt source.

Tried, no change. The 275V source measures 273V.

Recheck cap values that were replaced. C 40 will have most effect on height.

Rechecked, all caps look OK. I replaced C43 (.0015/1KV) by wiring two .0033/630V in series. In Sams, C44 is listed as .033, with .022 as an alternate value. I temporarily subbed a .022; no change.

I noticed one difference: R55 (between pin 8 and vert hold pot) should be 33K and I installed 39K for some reason. (Perhaps 39K is what I found there.) Not sure how important that is. I measure 8.6V on that pin; Sams calls for 7.5V and the Philco manual calls for 10V.

Make sure pin 7 measures 68 k to ground.

It measures 67.5 K.

Regards,

Phil Nelson