[Tom Albrecht]

Dave,

I've seen it done. When I got my Philco 48-2500 projection TV, a prior owner (an engineer) had unhooked the original HV supply, and built his own little HV supply with an 807 tube and a nice big RF coil for the HV. I hastily removed all that and put the set back to original, only to discover there was a good reason why he had done that -- the original HV supplies in those sets had too high of source impedance, resulting in fluctuating HV with scene brightness, which in turn affected focus stability.

So yes, I think that could work. I'll probably try that as a last resort if necessary. Hopefully I can either get a replacement flyback, or modify/repair the existing one in some manner that works OK. So one way or another, we'll get this problem solved! Glad to see lots of ideas here from you guys.

Tom C.,

The tripler idea sounds very interesting! On the Philco set mentioned above, I eventually replaced the original poorly-designed vacuum tube voltage tripler with a solid state tripler to improve the HV supply, so I have a little experience working with a tripler module. That would be a very nice fix that would fit into a small space somewhere and not look too crazy. If the drive right off the primary is high enough, then the original regulator, etc., should still be usable. It seems quite possible that this could work. I notice that the focus supply runs off a tap *below* the 6CD6 drive connection, and generates 4.5 kV with a simple half-wave rectifier. All I need is for the top of the primary to generate 6.7 kV to get enough to triple to 20 kV.

This might be the next thing I try after seeing if some minor surgery can remove the shorted turn. Easier than trying to rewind the HV winding or retrofit an HV winding from another flyback. I suppose I could even "borrow" the tripler out of my Philco to do a feasibility test, and then order another if the result looks viable.

I did check all the resistances, and they are quite close to the values on the Sams schematic. If it's a shorted turn, it seems to be isolated to just one turn or a small number of turns, having no appreciable effect on the total DC resistance of the winding.

Tom