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 Post subject: The Craftsmen RC 200 resto
PostPosted: Dec Fri 14, 2018 5:13 pm 
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Guys, you can thank shango066 for this question. I have a number of old tube TV's that's on my list to be repaired/restored. I have been away from TV for quite some years, and did repairs up until '02, when I 'retired'. One question I need clarification on is the best way to power up a TV that has been idle for 30-50 years. My inclination was to use a variac after testing for shorts. His advice tho was not to do that, since the horizontal oscillator may not start causing the output tube to fail. I also like to test without disturbing any of the tubes in fear to create a problem that wasn't there before. Shang pulled all the tubes, powered, then inserted the LV rectifier, then horizontal/HV tubes then vertical. I have had experiances where a radio worked fine until I pulled the tubes to clean things then never worked again. But, I want to check the TV before anything is disturbed to see what is there. I have never done a TV restoration, only radio, test equipment, amps and such. I'm all ears (and eyes). I have a mid '50's Travler and/or Craftsman that I want to go through for starters.

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Last edited by TV MAN on Jan Tue 08, 2019 5:58 am, edited 2 times in total.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 5:46 pm 
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Generally, it's not a good idea to apply power even with a variac to a vintage TV from the 60's or earlier that's been sitting unused for 30-50 years. You'd want to at least replace the power supply electrolytics first especially on transformer powered sets. If there's concern about the horiz osc working or not working, connecting a scope to the horizontal output tube grid will quickly verify that it's working and close to the right frequency in plenty of time to cut power before any damage occurs.

Of the two sets you mention, the Craftsman would be the better choice for first restoration as they were typically good quality TV's. Trav-Ler was a discount store entry level brand that usually represented minimalist design similar to Muntz. Their sets often worked marginally at best so save that one until you see what you can do with the Craftsman.

Since there are no OTA analog stations to pick up, you'll need a reliable signal source such as an RF modulator connected to a DVD player or similar to provide an analog TV signal for your sets. VCR's often don't work well on TV's that old.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 5:58 pm 
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I think the worry is that the horizontal output tube could start drawing current before the oscillator starts when slowly bringing up the voltage. You could remove just the horizontal output tube before applying power. Bringing it up without the rectifier first would let you check the power transformer if the set has one. Then put the rectifier back in and remove the horizontal output and test again.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 7:12 pm 
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The purpose of a Variac is to set the line voltage to the value the set is designed for.
It is NOT meant to bring the set up slowly until the smoke is released.

Before applying power, you need to test all inductors/transformers for open windings or shorts to chassis, test the tubes (particularly for shorts), and replace all filter capacitors.

Remove the LV rectifier(s) and power the set up briefly to confirm that all tube filaments light.

From there, I strongly suggest replacing any waxed tubular capacitors that connect to any node that has high voltage (B+) on it.

At that point, you can re-install the LV rectifier and turn the set on at nominal line voltage while monitoring line current, and observing B+ levels.

- Leigh

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 7:47 pm 
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Leigh wrote:
It is NOT meant to bring the set up slowly until the smoke is released.
- Leigh

I think the critical thing to do is to monitor the current if you did power it up gradually.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 8:32 pm 
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I don't see a problem with using a variac as long as you don't leave it at a voltage that is much too low.

Most important is to monitor current. Like Shango does, you should use an ammeter or wattmeter, like the Killawatt. If you are drawing 130 watts at 80 volts when maximum current should be 90 watts at 120 volts then you have a problem.


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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Fri 14, 2018 8:37 pm 
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Notimetolooz wrote:
Leigh wrote:
It is NOT meant to bring the set up slowly until the smoke is released.
- Leigh
I think the critical thing to do is to monitor the current if you did power it up gradually.
The critical point is that increased current only occurs AFTER a failure has occurred.

That fact does not change based on the manner of detecting the failure.

The rationale behind my recommendations is to avoid a failure in the first place.

- Leigh

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Sat 15, 2018 5:03 pm 
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Thanks for the advices. The Craftsman will probably be my first since its already on the bench. The picture tube tested good so it would be a good candidate. It uses the old selenium rectifiers with a power transformer. It doesn't look like it has been molested, aside from a few tubes. Ill check the transformer and filter caps for shorts. I may pull the horizontal output (and test), and pull the wire off the rectifiers to check the transformer. I can put current meter in place and try with the rectifiers. I am sure those will need replaced, and as Mr. Detrola mentioned the filter caps (which I may go ahead and replace the main filters to start with). I can scope the grid on the output tube with the tube pulled to avoid any excitement. I really don't want to pull more tubes until I have tried an initial power up.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Sat 15, 2018 6:56 pm 
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I think Leigh is too dogmatic. For post-1950 sets, I would first check with an ohmmeter
for dead shorts on the B+ and filament lines. Inspect all the parts for obvious flaws.
Remove every tube, one at a time, check it to see that it is in the right socket, check on a tube tester
and reinsert all but the rectifier. Then use a dim bulb and variac and raise the
voltage up to normal, very slowly. Check to see all the tubes light and there is no
magic smoke from shorts your ohmmeter didn't find. If the dim bulb starts glowing too much
stop.

Then the next step need experience. If you see known bad capacitior types like bumblebees
or certain other known bad brands (in British sets, "Hunts"), the first step is always
to replace ones that could short the B+ line or put too much positive grid bias on a tube.
(or if Hunts or equivalent, all of them).

Then remove the horizontal output, inset the rectifier, and try slowly turning up
on the dim bulb and variac, with a meter monitoring the B+. Watch for the bulb getting
brighter slowly as the "heater" tubes warm up. Normally this should be at a B+ well below
the electrolytic cap ratings. The problem with just turning on is that the B+ could
rise well above "normal" and instantly blow up (explode) bad caps, that would survive
slowly turning on ... but get warm. The key is to turn on slowly, every once in the while
turning off, waiting say 30 seconds and feeling all the electrolytics for getting hot.
You don't want them exploding in your hand. If they do get warm, replace all.
If all is well at say 75+ of normal B+,
check tube plate and screen voltages on the voltage chart for shorts. That includes
the missing horizontal output. If ANY show signs of a short, break down, replace ALL
paper caps. Then raise to 100+ B+ and recheck.

If all is well you probably want to replace at least the HV electrolytics next, even
if they don't get hot, unless they are post 1965. I always replace ALL
paper, oil, or plastic caps with more than 500 volts on them unless post 1965,
no matter what the grade. If they DID get hot, replace
ALL the electrolytics rated at more than 10 volts. I've never had a <10 volt
electrolytic go bad, and Steve McVoy agrees. At this point some people
would try with the horizontal tube in to get some idea if the set works, with
original electrolytics. The older the set, the less likely I'd do this.

For TV sets older than roughly 1950, I personally would start with a complete recap of
all paper and electrolytic caps with more than 10 volts on them before installing
the rectifier at all. For radios I might not do that if they are military grade under 600 volts.

Always check adjacent resistors while caps are out for replacement.

Its interesting to note the difference in advice on opposite sides of the Atlantic.
Our British friends are quite loathe to replace all paper or electrolytics, unless they
say "Hunts".


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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Sat 15, 2018 7:01 pm 
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Oh yes:

" I can scope the grid on the output tube with the tube pulled to avoid any excitement. I really don't want to pull more tubes until I have tried an initial power up."

OK, IF ... as I said before, if you can see the tube type that's OK. If you can't,
pull the tube and be sure its the right type. Every tube, every time! First!
I've seen tubes with wrong filament pins or reversed cathode-plate pins in a socket!


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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Sun 16, 2018 12:06 pm 
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TV sets used a secondary energy recovery system through the damper. As far as
under voltage/circuit failure modes one I did see was a crash of vertical sweep
that burnt a line into the phosphor of an aluminized CRT.

The customer (loudly) complained that it was our fault, (not denying it ) ,
and shop put a new tube in. We learned *never* to do what was done
again. :D

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Sun 16, 2018 9:08 pm 
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Anyone who has worked on the older equipment knows that the capacitors, especially the electrolytics, are a major weak spot. I prefer to do the recapping first, before applying power. As was mentioned, later stuff has a better chance of coming alive when cautiously powered up.

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 Post subject: Re: Powering up a set with a variac
PostPosted: Dec Tue 18, 2018 3:31 pm 
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Thanks for the replies. Here is the selected project, the Craftsmen. I need to check to see if I have the Sams on it. Looks like the correct tubes in the correct sockets exc a 6SL7 in place of a 6SN7 vertical osc. From the looks of the dust, nothing has been disturbed. Under chassis about the only thing I see that has been worked on is the power switch and rectifiers. The rest looks original. Lots of "bee's" underneath. I can see a couple of the electrolytics have leaked a little. Good thing is that it looks like I can get to about everything pretty easy for a recap. Picture tube checked good, gun looks shiny.

I did a few quick checks. The cord was deteriorated so bad I doubt it was even plugged in in the last 30 years. The fuse checked ok and get 2-3 ohms at the cord plug with the switch on. I don't see any obvious signs of a power transformer meltdown. The flyback looks to be in good shape as everything else in the HV box. This was a "junk store" find, way back in a corner, $10. Figured it was worth that for parts, esp if the big tube was good. Sadly, the cabinet got sold and the knobs were no where to be found. I am sure was 'repurposed', probably a dumb aquarium. They said it was a beauty. A day late and a dollar short. Well, at least I was able to save the chassis. It would only have been a matter of time until the neck got knocked off the tube. So, here begins the project. If I wreck it, it's just a chassis. If it lives, then it would be a pretty interesting piece of history.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Tue 18, 2018 8:14 pm 
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Agree it looks fairly original, that appears to be a replacement vertical blocking oscillator transformer near the center, with the Merit green label on it.

I believe these were only sold without cabinets for custom installation, which is why the chassis was chrome plated. Used to see these installed in walls, having the chassis sit on a shelf in a closet with the mask mounted to the wall was the most common method. So whatever cabinet it had been in was chosen by the original owner. Hopefully you can polish the chrome to look decent. I'd be tempted to just display it out in the open, a good conversation piece.

Save the bumblebee caps and sell them on eBay, should get enough money to pay for all the new electrolytic and mylar caps for the whole set.........

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Tue 18, 2018 8:25 pm 
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I have one and there is a thread on it here someplace. I will see if I can find it. This is a high end design and produces a better picture than most sets of this age. They were sold without a cabinet.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Wed 19, 2018 2:17 am 
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I kind of wondered about the oscillator transformer. It does seem to be a well built set, with some unusual features. I do wish it used tubes for the rectifier, oh well. It sounds like it is well worth a restoration attempt. I did locate the Sam's, so I have service info available. This will be nice to make some preliminary checks, and see what this gal is made of. Date says 7-1951. It sure looks ahead of it's time to me.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Wed 19, 2018 2:30 am 
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I see a bunch of Black Beauty capacitors (black plastic cylinders with color-code bands).
Those are quite unreliable. I strongly recommend replacing all of them before power-up.

- Leigh

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Wed 19, 2018 3:43 am 
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That Craftsmen looks like a wonderful project -- a high-quality set, and a not-too-cramped chassis that should be straightforward to recap.

Enjoy!

Phil Nelson
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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Wed 19, 2018 4:18 am 
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Agree that set looks like a very interesting and worthy candidate for a restoration. Should be a wonderful learning tool.


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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Wed 19, 2018 7:51 pm 
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I did some checks last night now that I have the schematic. I checked from B+ to chassis and no shorts. Found a 20a fuse in the 3a holder - not good. I disconnected the power transformer HV from the chassis, checked again for shorts. Then stuck a dim bulb tester and amp meter in the AC line, then did a slow power up via the variac. So far so good. Current stayed around .5 amp or so and the bulb was very dim. All the tubes lit, next I checked the output from the PT. I was at 216 ac across and 107, 106 to center tap. That was at 120v on the line. Looks like the transformer has hopes. Next, (don't shoot me!) I reconnected the PT leads and did a slow power up to about 50v, then again to about 70v while monitoring the B+ and current. I also had the scope on the H output grid. Current stayed near .7a, and the DC was sitting around 107 off L1, and 50 off L2. These are the 2 main B+ sources. I let it sit for a few minutes and powered off. To the touch I had a 400v cap under chassis barely warm and one of the cans. So I know there is some leakage. I didn't observe anything starting up like the H-osc, vertical or sound. I did note that it has had some vertical circuit work done, about all of it. Looks like an osc transformer, soldering around the sync amp and possibly a vertical output transformer. Typical. What is it about the vertical section that is always so troublesome? Even into the more modern sets. Oh well, more later.

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