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RCA 7T122 - Old as dirt    
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madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Sun Oct 02, 2016 2:37 am    Post subject: RCA 7T122 - Old as dirt Reply with quote

What can I say? I'm a sucker for a lonely antique sitting, abandoned, next to a garbage can. It's a 1951 RCA Victor B&W console TV, the first vintage TV I've owned.

Like this.

I didn't actually take any pics, it's... had a rough life. Anyway, the important question at hand, anybody here know anything about vintage electronics?

Initial inspection: It's been kept indoors and clean for most of its life. All the electronics are there and even in good shape, except the power cord was cut and the screen cathode wire apparently had a connector halfway down the wire that no longer exists. A close look shows nothing popped or burned, most likely everything as it was in 1961, the last tube replacement noted on the back cover in pencil. (I thought that was neat!)

Speaking of tubes, I've tested all of them with my grandpa's old Hickok 533A, found 3 bad, and 1 that's destroyed on the inside. I have replacements. I've also ordered all the replacement caps I'll need.

The real question is: how do I proceed? Do I risk plugging it in? I do have a variac. But even so, the last time I did that, with an old Simpson oscilloscope, it blew up a resistor so bad that I don't even know where one end of it was connected! Frankly I'm scared to plug it in just to blow something up, but at the same time, I feel like I should really replace one cap at a time and power up in between to see if it's improved or if I made it worse. If I replace them all at the same time, I'll be extra careful to get it right, but even my OCD can't prevent every mistake. Should I just say yolo and replace all 59 of the capacitors in one shot? Am I Mad for attempting such a venture? Will I ever stop asking questions?

Advice?
Google

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madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Wed Oct 05, 2016 8:13 pm    Post subject: Reply with quote

Ok, update. I attempted to test the crt, but without an actual crt tester... I have no idea what I'm looking at. I used the Hickok CRT adapter, but the thing is, the reading you get is on the 'english' scale, which means I have no quantifiable answer. The filament works, and I get the reading in the red/bad zone. However, according to the card that comes with the adapter:

Quote:
It is well to consider, however, several variations in cathode structure or composition in some tube types that will produce a reading in the "RED" or "DOUBTFUL" section of the meter scale on the tube tester although the tube itself may not be defective.

...some tubes may test in RED section and still be serviceable.


It also says that on other models, not mine, the tube is ok if it reads above the mark 'Rectifiers OK'... which this CRT is reading above. Also, this crt adapter has led me astray before. I tested my Simspon oscilloscope's crt on it before, and it read completely dead. I ordered a NIB crt, and guess what? That tested dead as well. So I don't trust the Hickok with anything but regular vacuum tubes.

TLDR: testing CRTs on the Hickok is just guesswork.

Should I drop $40 or so on an ebay CRT tester? I'm wondering if the rejuvenate function might breathe some life into this tube. I did try briefly upping the filament voltage, which does produce a *slightly* better result, but only while the voltage is upped.

Testing CRT

Oh yeah, I forgot to mention: this CRT has a steel bell. That's right, it's not one piece, which I thought would probably lose its seal over time, and apparently, that is a known problem. Oh, I did follow the procedure to test for gas, and it passed, but again, the Hickok...

I really want to save this old girl... Halp?


Pics or didn't happen:
Chassis
Sticker
kuhurdler



Joined: 28 Dec 2006
Posts: 2857
Location: Overland Park, KS

PostPosted: Thu Oct 06, 2016 7:00 am    Post subject: Reply with quote

I find this project incredibly fascinating, and am grateful for the opportunity observe what you're doing. I wish I could be helpful to you but I have never even seen inside something that old.
madmanmapper



Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Thu Oct 06, 2016 8:38 pm    Post subject: Reply with quote

kuhurdler wrote:
I have never even seen inside something that old.


That's a shame, I think you'd just love-love-love looking at what makes this old set tick. (And you thought a modern pcb looked messy!) I love old stuff, old tech even more. I've never really had the chance to work on something old like this either, well... minus my o-scope that I still haven't fixed.

In all honesty, I've lost a lot of hope with this tv. I bet the CRT has had it. I'm going to buy a crt tester anyway, add it to my collection I suppose.
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