Admiral 20Y4E chassis update:I need a h drive trimmer but suspect more problems also

[JCFitz]

Finally got the 1956 Admiral console I picked up a while back recapped and ready for testing for the 1st time this past weekend.Along with the recapping I found the vertical linearity pot was open.It was a 3k control.Among some controls I had I found a nos Zenith 5k.To bring it down some and hopefully protect the only 50v rated cap in parallel from overvoltage in case it was turned to maximum resistance I paralleled it with a 6.2 k which brought it to just under 3 k.Also the 8.2 k screen resistor and 100 ohm series resistor were fried. Remember I had a picture with a pulled in left side and a red HO tube plate.

Well I got full vertical and a good picture except for the width was in on the left some.The vertical lock is very critical. Will investigate later. Hope it's not the integrator,no values are printed for the internal components on the Sams.

My main problem is the horizontal drive. Still had the red plate and pulled in width even at full drive adjustment.Found the trimmer only measures 400pf at as tight as I care to adjust it.Sams says 170-780 mmf.Well I paralled it with some ceramic caps to try to get it to work for now. A 470pf which should be more than max value paralleled with the 400 pf of the trimmer should have been more than enough.I did get full raster but still could detect a slight red spot on the plate when the lights were turned off. Took the 470 pf out and paralleled 2 390 pf across the trimmer which in parallel which is almost 1200 pf. I would think I would have drive lines by now but it was just enough to stop all red plating.BTW this drive trimmer "is" the coupling capacitor in series between the horizontal oscillator and HO grid.

So first of all I need another trimmer since it only maxes out at half the rated max value. It is a mica trimmer on a ceramic base,chassis mounted Admiral part no.66A30-3.Anyone have any ideas where to find one?

2nd of all either it's supposed to go even higher in value or I still have a drive problem since technically I have 400 more pf in there than the trimmer was rated for and just get it working without cooking the plate.Shouldn't I get a drive line by now? I did find 2 out of tolerance resistors in the oscillator section but no improvement. The 1st the plate load for one section was supposed to be 5.6 k and measured 6.8k and the grid resistor on the 2nd section was (get this a carbon comp resistor drifted low) 135 k instead of 150k. Right now I have -32 volts on the grid. Sams calls for -28. The last oscillator plate is 145v exactly what Sams calls for.They call for 145v at the screen grid of the HO tube. That can't be right as the higher I make the drive the higher that voltage gets. I'm getting about 205v when it's running with my parallel capacitors and no red glow. About 195 v without and glowing red plate and pulled in width.

I need to get a scope in there and see if I have the required 80v pp at the grid of the HO tube and it looks right. I know something's not right here.

Btw I have a tests weak on a tube tester HO tube in there now for testing. The pulling in and glowing was much worse on a nos tube.Also the picture got very dark and it bloomed real bad in short order.The original HO tube was pretty cooked when I got this set.Also get this the picture is brighter and I have more boost voltage with the weaker tube.Also the flyback and yoke ring good on my Eico tester.

[bgadow]

I remember having a pile of old ceramic trimmers somewhere but I'm not sure where I "filed" them or how to measure their value. (are they usually marked?) I'll look around for them, in case somebody else doesn't turn one up. I have a couple junk chassis' in the attic, too (Philco, Zenith, maybe RCA) and maybe they have something.

[JCFitz]

I did find one when googling trimmer capacitors on the Sprague website.265-880 pf 500 wv .Seems like it will work. Turns out Mouser is a distrubutor and the exact same part is the only part they carry in stock in that capacitance range.Go figure. Guess I got lucky for once. Ordered it today. Will report back how it works next week when I receive it.