Starting a Restoration on a 1951 RCA 7T111B
 

I recently picked up an old RCA 7T111B with the KCS47GF-2 chassis from the estate of a RCA electrical engineer. I also got an RCA Gizmo from them. Apparently this set has been sitting for over 50 years and the previous owner either helped RCA invent their line of televisions or invented the color sets I'm not sure. But his son is in his 60s. Anyway I brought it home and I brought it up slowly on the variac and was surprised that I was able to get audio out of it and high voltage. I tried to get a picture but the controls are so dirty that I have to keep turning them side to side to see anything on the screen. I tested all the tubes and have a lot of tubes on order, the CRT tests very strong. So the next move is to pull the chassis and start replacing capacitors. I'm not sure how to get this chassis out. Almost everything is straightforward the only thing I don't understand is how to disconnect the high voltage it looks like the wire is built into the tube then comes back to the high voltage cage where it looks like there's some kind of a plug that's sitting in rubber have any of you come across this before?

After you discharge the HV- a wire from the chassis to the metal fitting at the end of the white wire, grasp the connector at the flange end of the white wire and gently rock it and pull straight up. It will unplug.

Without looking up the model or chassis just looking at the pictures it looks like that is a metal glass CRT. The "bell" or cone part is metal and it is all at High Voltage.
The HV lead is attached to the mounting hardware at the front of the CRT.
I believe that gizmo on the HV cage is a insulated connector. The wire attached to the CRT mounting has a sort of snap like connector that fits into the insulated connector. That is a bit of a reverse of the more common arrangement where the snap is on the wire coming from the HV cage and the connector connects to a small pocket on the side of a glass CRT.
BTW, the CRT mounting hardware has to have a layer of insulation between it and the rest of the TV. It probably is a sheet of plastic that is brittle by now.

Update I was able to pop the 2 metal parts apart and the chassis is out. I can't believe how many caps are in this thing I have a long road ahead.

These aren't bad caps wise compared to a 630 chassis or a early color set.

I've got a KCS-47 chassis laying around after filming this video this sat on Facebook vintage TV marketplace for dirt cheap and on the local marketplace for more expensive... After 2 weeks someone contacted me and wanted just the gutted cabinet...
https://m.youtube.com/watch?v=rQ99Xut9yrc

It has what looks like rubber that goes around the tube. I've never dealt with this type of Tube before, I was very surprised when I reached in to jiggle a tube, and the picture tube arched to my arm. Considering I've never been around a metal tube is there any different precautions when removing and reinstalling it? I have to remove the tube from the cabinet to remove the safety glass from the cabinet to clean some black goop off.

Do you know what CRT that is?
CRTs of that vintage and size often were tubes made with a metal cone between the glass screen and the glass neck section. There were mechanical problems making a CRT that was all glass that were later solved. The metal/glass tubes were lighter as an advantage at least.

The all glass tubes have a conductive coating (DAG) on the inside that is connected to the HV lead. (Later they applied a conductive coating also to the outside that was grounded. This formed a capacitor that helped smooth the HV charge.)

On a metal/glass tube the metal cone was used as the HV electrode. There is a HV cap (ceramic almost always) in the chassis that smooths the HV charge. The tube shell must be insulated from the chassis and other metal areas. The insulation can also form a capacitor that can hold a charge. It is always a good idea to discharge anything that is or was connected to the HV lead. So that means the metal cone as well as the HV cap in the chassis.
You will want to clean the insulation sheet and other parts but be careful not to damage them.

Tom I watched your video, I'm actually a big fan of you and Shango. I have a C3 also. I see you didn't unsolder one end before testing for leakage. Did you remove the tubes or anything before checking for leakage?

It probably looked like I didn't unsolder one leg of each cap because of editing (waiting 10+ seconds for each solder joint would probably bore a good part of the audience), but I did unsolder 1 leg of each cap before testing...I did notice if I left the TV chassis plugged into the variac the lead of the cap still connected would leak back to the C3 through the line cord and give some false leakage indication. So I was doing the cheeter cord hokey pokey each time I tested a cap. That line cord leakage was interesting to discover.

Thanks, for watching my videos!

It's a 17GP4 Picture tube.

I ordered my caps for this set and My Zenith last night. I'm not sure if I choose good enough caps. I didn't take the AC ripple into account. What do you guys think? I added the list for the RCA below

As far as I can tell those are fine. They really need to be compared to the specs on the service data however. The cap brands are fine.
If you need to fret over something make it that you connect them correctly.

Hey guys so I'm a little confused with the TV. I replaced all the capacitors, and then fired the set up I have sound, I could actually hear the snow and even the phono Port works. But I have no picture. The picture tube tests very high and has great cutoff, I took the plug off the back of the picture tube and compared all the readings with the Sams and they read correctly, and I know I have high voltage because I took a test lead attached it to the chassis put the other end on a screwdriver and reached into the high voltage cage and I'm able to jump a spark from both the 1B3GT and the 6BG6G tubes inside there. Where else should I be looking. The funny part is if I turn the selector down to phono leave it there for a few seconds then flip it back to television mode I'll get a quick white stripe across the screen that goes away.

1) your posted schematics are too blurry to read

2) Have you tried adjusting the ion trap?

https://live.staticflickr.com/65535/...b8159a3e_o.jpg

https://worldradiohistory.com/ARCHIV...l-VII-1951.pdf

Sorry I used adobe to convert the Sams PDF to an image. I'll try and get a better shot tonight. No I haven't touched anything else on the TV I thought I'd be chasing issues I created.

Did you adjust the ion trap?
Mark where it is now so you can get it back to the way it was if that is not the problem.

For some reason when ever I upload the pictures it scales them down and they become blurry. I can't share the PDF either.

So I fired up the set last night to move the ion trap, and noticed something. I'm very much a rookie so correct me if I'm wrong. I powered up the chassis on my work bench, I didn't have the picture tube hooked up and I jumped terminals 6 and 7 of the yoke plug, I could hear the thimping of the horizontal oscillator and the whine of the vertical. Now I only hear the whine. Should I be checking the horizontal oscillator first?

17GP4? Is that one if those wacky RCA sets with a 1V2 focus rectifier?

Yea it does have the 1V2. Why?

It was one of the first CRTs to use electrostatic focus. Much nicer than having a big, clunky electro-magnet on the neck to adjust. Downside is it requires around 3,000 volts.

They got that from a tap on the HV secondary and used the 1V2 to rectify it.

Later design got it down to around 500 volts which they could get from the boost voltage.

The set was originally owned by a engineer for RCA and I know it was available with the magnetic focus as well so I'm wondering if he opted for the better one.

Any ideas what I should check on my set Bob? I'm wondering about my theory with the horizontal oscillator?

Are you running the set without the yoke connected? That could cause it to behave oddly.

Hard to recommend what to check without knowing what equipment you have. If you have a scope, check the grid drive on the horizontal output tube and compare to the service info.

Also wondering if this set cuts off the picture tube when you're in phono mode. Could be the mode switch has dirty contacts.

I think the set does cut the tube off in phono mode. I have the chassis back in the cabinet and I have everything plugged in like it should be, I even replaced the dial light bulbs.

When the chassis was out I sprayed all the controls with contact cleaner a few times to get the gunk and dirt out then control cleaner and worked them back and forth. I think they're good.

I tested all the vacuum tubes and replaced the tired ones. My tube tester does have a plate cap, so I tested the horizontal output tube, and the high voltage rectifyer tubes.

I do have a set of test sockets that let me plug a tube in to the Tv chassis and give me tabs where I can check voltages. I don't have a scope, but I do have a DVOM that goes up to 600v.

The thing I find interesting is if I switch modes quickly I'll get a couple lines on the screen for a split second. I'm wondering if I'm not getting a negative voltage somewhere and flipping the switch is similating it?

I'm not sure if I'm looking at things the right way, but to get any kind of picture even a bad one, I need to get the horizontal running so I can get the line in the middle of the screen, then the vertical to fill the screen right?

But to get the horizontal working I need to look at the horizontal oscillator then the horizontal output? I'm trying to piece it all together from reading online and watching YouTube, and trying to find an order I should work in.

There is another test you can do on the horizontal that doesn't use any typical test equipment.
It requires that you have a fluorescent bulb however and they might be on their way out. Replaced with LED bulbs. The bulb does not have to work in a socket.

Hold the bulb near the flyback or horizontal output tube and it should glow.
It doesn't tell you the frequency is right and it doesn't tell you that the DC HV for the CRT is there. It is just another test.


Are you sure about the voltages on the CRT base? They could momentarily change when you change that switch.

After spraying controls don't overlook that the brightness control needs to be turned up in order to see a raster. Next step is to see if all DC voltages look reasonable at the CRT socket pins.

I went and bought a used high voltage tester off eBay. I hooked that up first to the Admiral and got 12,000 volts even though that TV calls for 16 and a half. When I hooked it up to the RCA I only got 4,000 volts. On the side of the door knob capacitor closest to the vacuum tube I can get my 4,000 volts along with at the high voltage connection. However on the other side of the door knob capacitor it doesn't register. Could this be a bad doorknob capacitor?

The other side of the doorknob cap is grounded so you shouldn't measure anything.

The HV probe could be somewhat inaccurate. None the less it is a good bet the HV in the set is too low.

Could be that the HV is being loaded down by leakage.
However the other voltages in the horizontal sweep circuit should be checked.

Try disconnecting the HV lead at the CRT and insulate it by putting the end in a jar. Then measure the voltage on the doorknob cap.

That's actually what I did and got my 4k volts

OK.
Well the doorknob might be bad, it happens. They are a little tough to find so it would be good to find the problem was somewhere else.
It could be the HV rectifier. The filament glow is hard to see.
Do you know if the horizontal frequency is right?
Did you measure what voltages that you can around the horizontal sweep circuit?
If you have a compact fluorescent bulb?
If you hold one near the horizontal output tube or flyback it should glow.

I might have a CFL bulb I have to look.

The 6GB6G rectifier tube tests good on my tube tester and shows no leakage. It's not super strong just in the middle and does have a little bit of a blue glow. The TV is off in the picture.

I don't know how to check frequency, is there a way without a scope?

I have those tube adapters that have tabs to check voltage so I will try to run through the horizontal circuit this weekend.

Hi Aperna1985,

Not scolding or playing Tube Nazi* here, but the 6GB6G is not a rectifier, it's the Horizontal Output :thmbsp:

* Think Seinfeld's "Soup Nazi", , , but for tubes...... :D

You're 100% right thank you. It's a 1B3GT which test strong actually. I could always buy another one in case.

Without something on the TV screen it is hard to estimate the horizontal frequency. A scope would also show the wave shape which is useful.
You don't need a scope for AM radios but working with TVs they are handy.

I don't suppose you have a frequency counter. I've never used a counter for that purpose but there may be a way to use it.

The fact that you got flashes of light on the screen when you changed a switch suggests the HV doorknob cap is OK. Also didn't you say you got a zap when you got to close to the side of the CRT? That would also suggest the cap is OK and there isn't too much leakage at any place else.