GE 800d Restoration

[Jon F]

Hey all, I'm starting on my 2nd restoration, a nice example of a GE 800d. I bought this off craigslist locally, and luckily it was in good shape especially the bakelite cabinet.

See pictures attached. I have a cap kit on order, and I have some leftover diodes from my previous restoration I can use in this set also. However it looks like one of the selenium rectifiers has already been replaced with a diode in a past repair? Hm. Everything else, including a vast majority of the tubes appear original.

Anything else to look out for in the set? I read about it having a hot chassis what extra precautions should I take? Also, the electro coating on the CRT, what is the purpose? Is the entire surface charged?

Thanks!

[Electronic M]

IIRC your only previous restoration was on an electrostaticly deflected set. With that in mind, there are some safety concerns on this to be mindful of. Hot chassis sets have one leg of the AC line connected to the chassis so if you touch the chassis and anything with a path to ground you are liable to get a nasty shock. You should look into getting a line isolation transformer to isolate the set from the direct DC path between the chassis and line that it has. Keep in mind that if you use any AC powered test equipment with the set while it is running without powering the set through an isolation transformer you may cause severe damage to your test equipment and or TV.

Next up is the HV system. Magnetic deflection sets tend to have much higher HV than electrostatic sets, and also tend to store that HV much longer. The coating on the outside of the CRT is grounded(or at least should be if nothing is wrong). That conductive coating along with the glass wall of the CRT and an internal coating form a capacitor. That capacitor integral to the CRT filters the HV, and also can store it for long after the set is powered off. Avoid working inside the HV cage or around the anode connector on the CRT bell when the set is on or the HV has not been manually discharged. Getting hit by HV, even stored charge from the CRT, is usually not fatal, but it can hurt pretty bad, and if it triggers your reflexes you can do a great deal of damage to your self and the set as your arm jerks back.

There are two ways to manually discharge CRTs: resistive discharge, and direct shorting. Resistive discharge is the better method and requires an HV probe (or some kind of homemade resistor probe) to bleed down the voltage over about a minutes time or less. Clip the ground of the probe to the chassis, and touch the tip to a bare HV contact and watch for the meeter to drop to 0.
The dead short method involves taking a WELL INSULATED screwdriver and using a jumper to connect the metal shaft to the chassis then touching the metal tip of the screw driver to a HV contact...If a loud POP is heard you had HV before the pop and have successfully discharged it. The downside to the short method is that after discharge the HV anode tends to 'recover' charge after a while and return to having HV on it(I'm not sure why though).

[cwmoser]

Hi Jon, I restored a GE 805 - very similar to your GE 800 -- about 2 years ago.
It was a fun project and these old GE TVs are super performers with very
nice video.

I would recommend you remove that Selinum and old Diode and replace with
1N4007 rectifiers and a 5 ohm high wattage resistor in series.

Here is my restoration thread:
http://antiqueradios.com/forums/view...p?f=3&t=189602

And, I recommend reviewing Tom Albrecht's notes about these TVs at:
http://www.radiomuseum.org/r/general...locomotiv.html
http://antiqueradios.com/forums/view...p?f=3&t=190884

You can download Schematics (Riders TV4) here:
http://www.earlytelevision.org/tv_sc...s_postwar.html

Carl

[Jon F]

Thanks guys, I've rebuilt a few arcade monitors in the past so I'm comfortable with discharging the CRT. I've been toying with buying a Sencore PR57 for a little while, I should probably pick one up.

Also thanks for the resources, definitely using 2 more of my 1N4007 diodes in this set.

[rca2000]

As to why the CRT "recovers" it's charge after a bit....OFTEN enough to bite you once again...has to do with the "time constant"--of its "capacitive effect". IN all reality--the glass envelope of a magnetic deflected CRT becomes a capacitor---and like any cap---there is a "time constant " that determines how fast its charge can drain off. It therefore takes a number of "hits" to drain the charge off completely. Others here may be able to explain this better than I can, but I HAVE been bitten by an anode after discharging it a NUMBER Of times. SO, be careful.

[bandersen]

From Wikipedia http://en.wikipedia.org/wiki/Dielectric_absorption

Dielectric absorption is the name given to the effect by which a capacitor that has been charged for a long time discharges only incompletely when briefly discharged. Although an ideal capacitor would remain at zero volts after being discharged, real capacitors will develop a small voltage coming from time-delayed dipole discharging, a phenomenon that is also called dielectric relaxation, "soakage" or "battery action".

[cwmoser]

Bob, that is something I have wondered about.
Thanks for the explaination behind it.

Carl

[Electronic M]

Originally Posted by cwmoser

Bob, that is something I have wondered about.
Thanks for the explaination behind it.

Carl

Ditto, it seemed strange/impossible for it to be able to regain voltage after being discharged to 0V without that explanation. I've found resistive discharge prevents it from bouncing back.

[Jon F]

Update on the set:

-3/4 of the way through the recap job, i still have 9 paper caps and 1 small ecap to go.
-Replaced the selenium rectifier and old diode with 1N4007 and 20ohm resistors.
-Replaced the HV lead to the CRT with a modern one.
-Replaced globar resistors. Old ones tested at 900 and 1300 ohms. Spec is 75 ohms!!
-Readjusted the ion trap and all basic controls.

Some progress as you can see from the picture. Not enough vertical size and horizontal is way too wide. Neither it adjustable better than that. Sound is good.

The speaker cone is damaged, is it a standard replacement or do I need to send it out for rebuild?

[Phil Nelson]

I have patched many tears and small holes in speakers with tea bag paper and flexible glue. You can also buy GC Service Cement, but I don't know whether it's really worth buying a special-purpose glue.

TVs have relatively low-fi audio (small speaker, rudimentary circuitry), so a nicely patched speaker will sound no worse than a new one. If the old cone is completely ruined, then of course you'll need to recone or get a new speaker.

That picture looks promising. If you have already finished a basic recap of the vertical and horizontal circuits, I would look next at mica caps (if there are any) and resistors there.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Jon F]

Finished replacing all of the paper and electrolytic caps. Horizontal width is now good but vertical height, while improved, is still too low.

Any tubes that could cause this or should I start hunting down out of spec resistors? How do I test Mica caps/ what do I need to buy to do so?

Thanks!

[Jon F]

I found the culprit, R296 was twice its nominal value of 4.3Mohm. Replacing this resistor brought the height back to normal.

After the TV warms up the picture stabilizes mostly, but it is still a little twitchy.

Everything was working OK last night, then today I powered up the set and after a few minutes adjusted the vert hold and POOF, the CRT went blank. No bad sound or smoke, and everything else still worked.

Any ideas?

[Electronic M]

It is either loss of HV or a CRT bias issue. Check the HV first. It is easier to check and more common to fail.

[Jon F]

I found the rear horz hold control is broken and was intermittent grounding to the chassis. Mainly because I tried to adjust it and spun it around so part of it was grounding.

Can I bypass this control? There already is a horz hold on the front of the TV.

[Jon F]

Also have a horz linearity issue that may or may not be related: