Starting a Restoration on a 1951 RCA 7T111B - Page 2 - Videokarma.org TV - Video

old_tv_nut · #16 08-01-2022, 10:14 PM

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

Aperna1985 · #17 08-02-2022, 08:13 AM

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.

Notimetolooz · #18 08-02-2022, 09:27 AM

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.

Aperna1985 · #19 08-02-2022, 10:20 AM

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

Aperna1985 · #20 08-04-2022, 01:42 PM

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?

nasadowsk · #21 08-04-2022, 03:35 PM

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

Aperna1985 · #22 08-04-2022, 04:34 PM

Yea it does have the 1V2. Why?

bandersen · #23 08-04-2022, 04:55 PM

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.

Aperna1985 · #24 08-04-2022, 06:30 PM

Quote:

Originally Posted by bandersen

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?

bandersen · #25 08-05-2022, 09:53 AM

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.

Aperna1985 · #26 08-05-2022, 11:05 AM

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.

Notimetolooz · #27 08-06-2022, 08:56 AM

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.

Kevin Kuehn · #28 08-06-2022, 11:02 AM

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.

Aperna1985 · #29 08-15-2022, 02:21 PM

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?

bandersen · #30 08-15-2022, 05:08 PM

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