Hallicrafters T-506 Late Production Set

[Tom Albrecht]

Originally Posted by M3-SRT8

Like a dummy, I only ordered two 470pF 15kV axial caps. I need four.

Can I substitute ceramic disc caps? Two are in the HV Cage, two underneath near the bleeder resistors. The parts list calls for 500pF 6kV.

You can give the ceramic caps a try, but they might not work well. I did a study of this a few years ago and was able to show how the applied DC voltage across high voltage ceramic caps actually changes their capacitance. This causes severe distortion of the scanned raster.

That problem, however, is mainly with vertical deflection. In your set, those use much larger value capacitors like .01 uF (or I believe even .05 uF in the Hallicrafters). Your 470 pF caps are probably for horizontal deflection or HV filtering, which have less of a problem with this.

What I found with ceramic capacitors is that if you simply use a significantly higher capacitance value than the original tubular capacitor, ceramic will work. So for example, if you see problems using 470 pF ceramic capacitors, then using something like 2000 pF (.002 uF) or more will probably work just fine. Maybe even .001 uF would do the trick.

For some of my previous work on this subject, see: http://www.videokarma.org/showthread...=260749&page=2

I have a more complete write up of it somewhere else, but I can't find a link to it right now.