Sentinel 430 restoration

[Jeffhs]

Originally Posted by cwmoser

Well I be darn. Did not know.
Never heard of a TV lamp.
Even not knowing, they are still visually appealing.
I guess this shows that some designs are timeless.

TV lamps were used to provide a soft light on top of the set so that the room in which the set was located wasn't totally dark when the TV set was on, per recommendations by eye doctors of the time (1950s) discouraging watching television in pitch darkness. IIRC, my folks had one of these TV lamps on top of our first set; it was in the shape of a horse, with a little 7-watt Christmas tree bulb in the base.

Some of the fancier TV lamps even included a digital clock in the base. One manufacturer of these lamps (don't recall whom right now) had a TV lamp that was actually shaped like a miniature television, with the clock in the center of the "screen" and the lamp arranged so that it illuminated the area around that screen and the clock as well. The clock mechanisms were motor-driven digital clocks made by well-known companies such as Pennwood Numechron, the same folks who brought us the first motor-driven electric digital clocks.

I wouldn't be surprised if we eventually see a comeback of these TV lamp clocks, with updated designs, including LED clocks, of course. The diffuser could be in the shape of a current TV actor or prop from a popular show, and the lamp bulb would probably be an energy-saving LED or other low-power light source.

[bandersen]

I have a few of those numechrons too.

[Kevin Kuehn]

Thought I'd bump this thread to the top because Bob's done a couple recent reveiw videos on this set. I've been finding it very fascinating because I picked up this sets bigger brother earlier this fall. Basically it's the same chassis but with a 19AP4 CRT. Originally I picked up the model 425-CV because I was in need of a good 19AP4 for my DuMont RA-119. But the more time I spent researching the Sentinel, the more I wanted to keep it complete. Recently I finished restoring the chassis. The cabinet is in decent shape and only needs a little touching up. I currently have the chassis back in the cabinet and have been watching it over the holidays. Turns out it's a fine performing set.



http://s452.photobucket.com/user/Kue...Sentinel%20525

[bandersen]

Beautiful set I hope you had an easier time with service info that I have. I've never found a 430 specific schematic and the 423/425 info doesn't quite match mine.

So as Kevin mentioned, I have pulled the Sentinel out for some servicing. All this time I've been running it on the weak CRT it came with but it's nearly dead and needs replacing.



I guess the sales flyer claim of 17" was accurate after all.


Here's a shot of how the set was playing. The CRT lacks focus and it gets worse as the brightness is increased.


Back when I got this set I had assumed it had an early 16" CRT in it, but it turns out I was wrong. If I had just peeled back the rubber trip on the CRT I would have found this label showing it's a rebuilt 17BP4!

So I can't really using the nice aluminized 16KP4 I found I do have a couple good 17BP4s although neither is aluminized. I chose the one with the best external coating and installed it.
That's too bad though because it means my 17T13 with dead CRT will have to wait. I then checked all the tubes, found six weak and/or shorted and replaced them.

[bandersen]

Back when I restored this set the first time around, I had noticed a gradient in the brightness. Here's a shot of the same issue with the new CRT. I suspected it had to do with the vertical retrace blanking circuit. So I disconnected it and the brightness is now uniform but the retrace lines are back. I'll play around with different RC values and see if I can get it working correctly.

[Kevin Kuehn]

Think I ended up with a .01uf and a 5.6k in series for retrace blanking. There's definitively a trade off between max blanking and brightness at the top of the screen, as well as overall condition of your CRT.

[bandersen]

Here's the signal on the cathode. It's pretty obvious now why there's a brightness gradient.
I reduced the cap from 0.1 to 0.01 and increase the resistor from 1.5K to 5.1K and it helped a lot