GE 805 Focus Coil Question
 

I just acquired a chassis for the 805 but the bracket for the focus coil mount had been ripped off the yoke surround. It was held by 3 rivets. I repaired and reattached the coil bracket but it required an almost complete disassembly of the coil/yoke bracketing assembly.

I'm taking a different approach to my restorations. Instead of the capacitor shotgun, I'm attempting to do as much as I can to see what's possible on original components where that can be done without risking unobtanium parts. The 805 does not have a power transformer and is series string. I brought it up through the dim bulb steps and I have sound and HV but no light on the screen. The 10BP4 has an ion trap. I think I'm working with 2 variables and that always creates a bunch of possibilities...the position of the focus coil (no original reference since it was removed and a multi position range of motion) and the ion trap. Does anyone have any information specific to the 805 or know of a methodology as to where to start this process of finding the sweet spot for both of these? Or am I wrong and these 2 hardware pieces have nothing to do with one another as far as producing light on the screen?

Thanks!

Chris

They do both have an effect, but I would expect the on trap to have a bigger one. Have you tried moving the ion trap magnet all around, slide up and down the neck and flip it around?

I have not turned it around because it has an orientation arrow on it for facing forward but I'll try it. I have not gone all the way around yet...maybe a 230 degree sweep with the top of the neck as the apex. I'll try more comprehensively tonight starting close to the back of the focus coil, tracing a 360 degree arc around the neck and then move it back 1/8" and do the same. I've worked on another one of these and the perfect spot occurs in a very small area on the tube neck.

Thanks Bob

Don't worry about being aggressive. Go 360 and as far up and down as you can. you won't hurt anything. The worst thing you can do is leave it running in the wrong position for long.

The electron beam is hitting internal metal elements in the gun. Eventually, metal will vaporize and reposit elsewhere. Potentially causing a splotch on the screen

On a sort of related subject, back before aluminizing, they had to have made many bent beam type CRTs and even some after that were aluminized, so there had to have been many thousands if not even millions of them, and ion traps for each of them, don't the ion traps outlast the tubes they were with? So you would think there would be lots of them out there, but they seem to be rare, as do focus magnets, weird.

I have some spares. I find them in service caddies and junk boxes occasionally and have a few from sets I've scrapped...most end up buried in 3-5 of my junk boxes.

Oh no...OK...Thanks Bob!

Has anyone tried one of the adjustable ion traps? I obtained one NOS. It was an aftermarket replacement back in the day. It consists of a metal rectangular surround with a magnet slug in it, its position varied by a screw. There are 2 tabs at the ends of the box for the spring that holds it on the neck. It can be positioned like any ion trap and the magnet can be moved from left to right at right angles to the neck using the screw. I'll post a picture later but I'm asking if anyone has used one and was it helpful?

"Capacitor Shotgun" sounds suspiciously like a railgun countdown sequencer.


:D

I have only ever found one aftermarket trap on evil-bay, and this was years ago before I knew that the original one for my 12LP4 was NOT lost in all the moves over the years and was OK, it too was a dual, but seemed way too strong for the tube comparatively, not sure what it's used on, still have it, however.
I still look from time to time out of curiosity, but have not seen any others since.
I have heard tell of adjustable ones, but never seen one. ( adjustable gauss )

I have one but have never used it since I don't know how to set the strength.
They are kind of a pain to storage and organize. They stick together which may effect strength over time. I image most were tossed along with the sets.

No joy...and I was pretty comprehensive. So, I have sound, high voltage at 8kv, and a glowing filament in the 10BP4. Does the HV and the filament mean I should get light on the screen if I find the right place for the ion trap or should I check into other things and make sure they are right first? The 10BP4 is a good tube...I have used it in another TV. The components are mostly original but there has been some tinkering in the past...rectifier swap to 2 1N4007 with a dropping resistor and a couple of waxies replaced but that's about it. The TV was brought up through a light bulb series and now it's fine on 117 line AC and pulls about 1.25 amps. :scratch2::scratch2::scratch2::scratch2::scratch2:

I would check voltages at the base of the crt, cathode, grid 1 and grid 2 and compare to values on the sams schematic.

jr

+1 grid and cathode voltage are probably the most important followed by G2.

If the chassis is biasing it hard into cutoff you could stick a straight gun aluminized tube in there and it'd still be dark.

The Sams gives voltages for the 12” version but I used them as a reference anyway. The cathode is supposed to be 365v DC and I’ve got 345v. G2 should be 100v and I’ve got 210v. When I was fishing to see if I could find a place to check G1, I found a 0.1uf cap connected between the lead going to the CRT and a coil had broken off of its solder tab. Of course at that moment I had to go upstairs and shut down for the night but I’m hoping that solves the issue. We’ll see. I wonder if the loss of that cap in the circuit could have led to the G2 voltage doubling?

These voltages are not correct. I read:

Pin 2, g1 .2 volt
Pin 10, g2 320 volts
Pin 11, cathode 0 to 110 volts varies with brightness control setting.

jr

Can I ask where you found those voltages because, as I said, the sams has voltages for the 12KP4 but not the 10BP4. Also, is that voltage for G1 0.2 volts?

I'm reading directly from the Sams:
Pin 2, G1 3.1 volt
Pin 10, G2 365 volts
Pin 11, Cathode 100 volts

Like I said, this is for the 12KP4.

Got the Riders service data now. Much more comprehensive.

I used this :

http://www.earlytelevision.org/pdf/g...sams_125-7.pdf

It may not be absolutely correct for your set, but the CRT voltages are close.

jr

No matter which reference you read, the cathode should not be higher than g2.

jr

The Riders for the 805 chassis (also at the ETM site) has multiple versions of the TV by chassis revision and I think I found the correct specs and schematic for my chassis. It's an 805 U chassis having a cathode voltage of 340V, G1 at 110V and G2 at 25V. There is a note for the G2 voltage saying it's measured on a 50V scale (I'm assuming on a VTVM?) but that's just going to make he reading more precise on the old voltage meter correct?

Those voltages appear to be mixed up, CRT would be biased off. I would believe:

cathode 110v
g1 25v
g2 340v

would work.

I must have the T or S version because this is exactly what I have. C269 is the capacitor that broke off its solder tab on the L258 coil side. Pin 10 is supposed to be 340V and I have 345V. Pin 11 is supposed to be 110V and I have 210V. Could the broken C269 capacitor solder joint account for the voltage being 100V higher on pin 11?

https://imagizer.imageshack.com/img922/8686/UCJ5QQ.jpg

...and you're right, I did mix up the voltage designations...that's why I'm sticking with pin # for now!!!

I would also check the caps/voltages around the brightness control. I suspect more problems than just the solder joint (should be able to vary control to get the cathode voltage closer to the g1 voltage to obtain the brightest picture ). :scratch2:

Also check the cap connected to the dc restorer.

jr

Replaced C269

cathode 130v
g1 2.5v
g2 345v

I think I'll try the ion trap again tonight after replacing the additional caps you suggested.

Does varying the brightness control bring the cathode voltage closer to the g1 voltage?

jr

No it does not

The cathode voltage does vary from 130 to around 260 when the brightness pot is turned to the halfway position. G1 doesnt change nor does G1

C270 is a 0.2uf original wax cap. I'll replace it.

Reads 0.3uf and it leaks at 25 volts. It's a 400V capacitor

I suspect leaky/shorted caps in the circuit surrounding the brightness control.:scratch2:

C-303 would be my most likely suspect.

jr

The first one certainly was. I bumped it up to 450 volts for a few seconds on the capacitor tester just to be sure it was full of electrons but no eye opening at 25V.

That did it...changing those caps! A slight adjustment of the ion trap and I got a bright static picture in good focus. Fantastic. Thank you for all of your help!

Looks like the brightness pot is shot. It only works turned all the way up. Once it's moved from the extreme brightness position, it goes dark. It's a 500k pot but it's double shafted and ganged with the contrast pot. I think Ill put a new carbon linear 500K pot on the back of the chassis for brightness and leave the original pot in place as an inactive control for the aesthetics. Once I set the brightness, there's little need to screw with it anyway and I'll position it so it's accessible from the back of the cabinet.

Have you checked the pot with an ohm meter?

jr

Mark Oppat should be able to make you a new control given enough information.

No, not yet. I have another one of these and the brightness pot failed on that one as well. I wonder if this is a design issue. I will check it but what else could account for the lack of adjustability?

The name is familiar but I don't know who that is nor do I know how to get in touch.

Found it and the website. Thanks Tom