On the bench: Sentinel 400TV

[Kamakiri]

Well, managed to pick up one of these on a barter deal yesterday, always wanted one of these.

This particular one's been recapped completely, with the exception of the 6 kV caps, which I need to order up. My guess is that the guy who did the job didn't have access to them. I have to say, the work done on this chassis was VERY neat.

Tested the tubes, replaced some, but on the schematic on the inside of the set, the 12AT7 in the tuner was crossed out in pencil, and 6C4 written on the diagram.



Since the 6C4 has a 7 pin base, and the TV had a 7 pin base, and the 12AT7 doesn't, I put a 6C4 in as the diagram said. I don't know if this tuner has been replaced before, but it's marked as being a Sarkes-Tarzian with a stamp date of sometime in Feb 1949.

Long story short, powered it up on a variac, all the filaments including the picture tube are lit, no raster, no audio, but no smoke. Think this thing did have a tuner substitution at one time?

[decojoe67]

Just wanted to mention that it's great to see one of them with the darker covering. So many of these have the tan color. I had one like that, elec. restored and it played practically flawless.
Good luck with it.

[earlyfilm]

Originally Posted by Kamakiri

Tested the tubes, replaced some, but on the schematic on the inside of the set, the 12AT7 in the tuner was crossed out in pencil, and 6C4 written on the diagram. . . . . I don't know if this tuner has been replaced before, but it's marked as being a Sarkes-Tarzian with a stamp date of sometime in Feb 1949.

I'd guess this was a factory substitution of a newer 1949 model tuner that was made when Tele-Tone manufactured your set.

There is a schematic of both your set model and a Tele-Tone made set with the 6C5 tuner at:

http://www.earlytelevision.org/tv_sc..._diagrams.html

To find what probably is your ST tuner, look at the Airline 94SE-3018A schematic on the same page.

James

[Kamakiri]

This set is turning into some weird nightmare......

Let me start by saying that there was a recap done on this set by God knows who, but I have to say that they did excellent board work.

First issue. Take a look at the differences under the HV section. Note that there is a resistor unhooked as well as a new blue HV cap....that's my work. The resistor was charred on the end, so I figured I'd pull it out and stick a new one in....when I lifted the one leg of the resistor it popped back with force, as if it has been stretched. I was going to finish soldering the other half of the blue cap when I noticed that according to the Riders, everything looked wrong. Decided to get a copy of the Sams, and note the difference in the stuff that's there.

I admit, I did snicker when I saw the Sams illustrating a cap that looks like it has a venereal disease right from the factory

[Kamakiri]

Now here's issue #2, also on the sweep chassis. The 100 uF capacitor was disconnected at the positive lead, the negative lead was still hooked up, and nothing was ever put in place. Okay, so someone cut out a wire, I can figure this out.

Then, I looked at the Sams. Again, makes no sense. I've noted both the pictures as to what I can see.

Did someone have their hands in way too deep in this set, or is the Sams horribly wrong?

According to what I'm showing, R109 is in completely the wrong place, yet the Sams chassis picture shows the wiring to appear accurate, at least where R109 is concerned.

[John Folsom]

The neg. side of the 100uf should go to the plug pin 12. the positive side goes to one end of the 10 ohm power resistor, the other end of the resistor goes to the junction of the two rectifiers. Of course, since the R and C are in series, their order order can be swapped with no difference in performance.

[Kamakiri]

Thanks....so all I need to do is insert a 100 uF cap, basically.

Any thoughts on the mess under the HV section?

[Tom Albrecht]

I just worked on two of these. Both were pretty close to the Sams in the HV section. I'd recommend rewiring yours to follow the Sams diagram. I can attest that it works fine if it matches Sams. No need for any doorknob caps under the HV chassis. Just use 1000 V tubulars on the B boost (output from 6X5 rectifier) and 630 tubulars everywhere else (except under the main chassis, obviously, where the HV coupling caps are). If you need any under chassis pics of a working set, just let me know.

[Kamakiri]

Originally Posted by Tom Albrecht

I just worked on two of these. Both were pretty close to the Sams in the HV section. I'd recommend rewiring yours to follow the Sams diagram. I can attest that it works fine if it matches Sams. No need for any doorknob caps under the HV chassis. Just use 1000 V tubulars on the B boost (output from 6X5 rectifier) and 630 tubulars everywhere else (except under the main chassis, obviously, where the HV coupling caps are). If you need any under chassis pics of a working set, just let me know.

I think I'll have to take you up on that, I'd very much appreciate it. What I really need are a couple really good shots of the underside of the HV sub-chassis. This thing is an absolute mess, and the black-and-white Sams pics only go so far.....

The sweep chassis itself I believe is all set to go. Got that cap wired in, and replaced the nasty 10 ohm resistor while I was there. The schematic showed a 2 watt, but I happened to have a 10 watt handy that fit in just right.

[Kamakiri]

Tom or anyone that happens to have a Sentinel, if you'd be willing to take a couple detailed shots of the underside of the HV section, I'd really appreciate it. I'm freed up enough to get back on this troublemaker

[Tom Albrecht]

Unfortunately I don't have access to mine for about a week and a half.

[Kamakiri]

No rush, I really appreciate it....

[earlyfilm]

Originally Posted by Kamakiri

. . . . . on the schematic on the inside of the set, the 12AT7 in the tuner was crossed out in pencil, and 6C4 written on the diagram.

One of my sets has a tuner with 12AT7, 6AG5 & 6BH6, while the other has 6C5, 6AG5 & 6BH6 crossed-out in pencil and 6AG5 written in. I marked my pictures to indicate which chassis they are from.

Originally Posted by Kamakiri

http://www.videokarma.org/attachment...4&d=1394801806

http://www.videokarma.org/attachment...5&d=1394801812

It's Sam's that is incorrect. The photo in Sam's is missing one connecting wire and a few other parts.

This chassis was available for over 2 years under at least 4 brands and probably more, so production changes are expected.

Your former recapper must have lengthened the wires, because the factory wires are too short to get a full view of the underside.

Originally Posted by Kamakiri

http://www.videokarma.org/attachment...6&d=1394801959

Your set is missing a black wire connecting the B+ limiting resistor 7.5 Ω or 10 Ω resistor and the 100 µFd electrolytic.

Also below are photos illustrating the chassis with the 6C5 and 12AT7 tuners.

If you or anyone wants a higher resolution copy of these, just shoot me an email, as VK compresses photos. If you need see a better view of the underside of the three tube sub-chassis, I'll do it, but it may take a week or so, as I have to clear my workbench first to unsolder and mark the seven leads.

Sorry for the rant, but I've gotta find a source for traditional lamps. These pigtails make color codes hard to read and give you a completely different color when taking two photographs shot seconds apart, without touching the lights.

James

[compucat]

Originally Posted by earlyfilm

One of my sets has a tuner with 12AT7, 6AG5 & 6BH6, while the other has 6C5, 6AG5 & 6BH6 crossed-out in pencil and 6AG5 written in. I marked my pictures to indicate which chassis they are from.



It's Sam's that is incorrect. The photo in Sam's is missing one connecting wire and a few other parts.

This chassis was available for over 2 years under at least 4 brands and probably more, so production changes are expected.

Your former recapper must have lengthened the wires, because the factory wires are too short to get a full view of the underside.



Your set is missing a black wire connecting the B+ limiting resistor 7.5 Ω or 10 Ω resistor and the 100 µFd electrolytic.

Also below are photos illustrating the chassis with the 6C5 and 12AT7 tuners.

If you or anyone wants a higher resolution copy of these, just shoot me an email, as VK compresses photos. If you need see a better view of the underside of the three tube sub-chassis, I'll do it, but it may take a week or so, as I have to clear my workbench first to unsolder and mark the seven leads.

Sorry for the rant, but I've gotta find a source for traditional lamps. These pigtails make color codes hard to read and give you a completely different color when taking two photographs shot seconds apart, without touching the lights.

James

You might try using LED lamps. They give much better color rendition than compact fluorescents. It is a more pleasing type of light as well.

[Kamakiri]

Appreciate the pics. I'll get it up on the bench tomorrow and see if I can sort some of this out....