1956 Admiral solid state HV rectifier modification
 

Since I have been unable to replace the high voltage rectifier cup in the 1956 Admiral 20Y4E I have posted about in the past I have followed a suggestion to convert it to solid state.

I don't have a load of old tv chassis or parts but I did have an old stick rectifier from a solid state color tv I junked years ago.I did utilize the old HV cup as a holder and to help insulate the rectifier from the chassis. I knocked the old tube socket which was glued in place inside the cup out and found a nylon washer that fit in the hole and held the stick rectifier snugly in place.

To insulate the output I put both the focus rectifier rubber cap and hv rectifier rubber cap from a dead Philips/Magnavox flyback concentrically over the bare male part of the HV stick rectifier. to make doubly sure that it was sealed from air and possibility of corona I also used a thick rubber piece salvaged from an old Philips/Magvavox HV section on top of the output of the outer cup and new HV lead. All of this was covered in heat shrink.

The old heater leads are covered with heat shrink and tied behind the chassis if anyone ever wants to convert it back to a tube rectifier. I really went out of my way to insulate the rectified HV completely from open air.


http://www.youtube.com/watch?v=_KlBzI3zcpM

I'm happy to say this works great as far as I can tell. I heard a couple of ticks when HV first came up and then blissful silence except for the normal sounds of a tube tv chassis operating.I can stand in back of it and listen and no ticking or corona of any kind. :banana:

I was kinda worried about not having enough hv with a color rectifier but actually I may have more. I got plenty of brightness and it only blooms slightly if I turn it all the way up. It did that before so no worries there. I am wondering if I'm a little high on the HV.I'll have to bring home the HV probe from the shop to check it.

The schematic calls for 14.5 kv.does anyone have specs for maximum hv for a 21ALP4? Of course I don't know what my HV is running yet.It may be brighter because the ticking was pulling down the HV.Also that intermittent vertical height jump has not reared its ugly head at all.

10-12 KV would be expected for a 12" CRT. Make sure the dag is grounded so the CRT capcitance will help hold the voltage up. Not sure what the voltage drop is across the SS rectifier would be but the fact it came from a color application means it certainly will handle the current.

CONGRATS!

Congraddamalations on the mod, JC. :beerchug:When you taped off the unused filament winding, you left the ends not shorted
together, right? Bill(oc)

Hello,

Here is a spec sheet for your CRT. Good luck with your project!

http://home.comcast.net/~tubes/Syl55/Get_Page.html?368

Yeah. They're covered in heat shrink tubing.:) Check out my youtube vide I added to the 1st post. Hope I don't sound too dumb.:o

Measured the high voltage last night. It rubs slightly high when the line voltage is set to give the B+ Sams calls for.B+ at 265v line voltage 113v yields about 15.3 kv at 0 brightness. At straight plug in on around 122v line gives about 17kv. Higher than called for of course but so is the line voltage and B+. It's still under the 18kv max.

Also the horizontal drive has some effect on this as expected. I had too much at first and almost the 18kv at full 122v line as there was a slight drive line on the right and I could see nonlinearity in movement in that area. I gotta get a pattern generator hooked up to get it set right (Hope that Sencore VA62 I bought off ebay awhile back works) but it's much closer to what it should be now.