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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Thu 20, 2018 5:03 am 
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I worked on sets like that one back in the 'day' HEAVY!

I still have the chassis from a Westinghouse that originally had a Bakelite
cabinet.

The Westinghouse was modified to provide signals for project 'Vid-Syn' .

That could produce a raster with XY but no Z signals.

I never worked on a set with a magic eye.

Those sets ate tubes in family use of 9 or so hours a day.

Fine, because we sold tubes on service calls.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Dec Tue 25, 2018 1:01 am 
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Here is the thread on my set viewtopic.php?f=3&t=109246

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Fri 04, 2019 6:26 am 
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I did a slow power up without the bulb in the circuit. It was dropping the current enough that nothing would work. I monitored the current and it was in the 1.5 amp range. I could get some static in the sound, hear the vertical running and the horizontal, but it seemed a little upset over something and I only had about 2kv on the high voltage. I did some checks around the horizontal and damper and found the voltages close enough. So I did a test on the HV tube and found it dead. I found one in a junk box and it at least moved the meter on the tube tester so I put it in and this is what I got:
Attachment:
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DSC05458.JPG [ 86.41 KiB | Viewed 1128 times ]

I have about 14kv on the meter now. No video or sound. Flashes when I change channels. I think this is a split carrier set, so I'm betting something in the tuner. Typical vertical sweep issues. That's as far as I got.

Thanks Tom for your link to your restoration. Gonna have some caps to change.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Fri 04, 2019 6:08 pm 
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That's really promising, so far. Change out the paper caps now and it should improve the vertical. Have you verified on another analog set that your signal source is putting out a viewable picture on whatever channel you are using for testing? Generally after a few years the contacts on those tuners need attention, they oxidize and don't make connection.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 5:01 am 
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I did verify my video source and it is working. I cant tell what channel it is on because I dont have the correct knob. My B+ is a little low, so that could be affecting things. I did start some recapping in the vertical section. I replaced the cathode bypass C6 and powered up with little change. I started to replace the other caps, C82, 83 and 84. I checked R95 which checks in the 13k-14k instead f 8.2km and r100 checks 3.3 meg. R94 checks ok. So, I read in Toms post about some changes in the circuit. So, I dont want to replace with the wrong values. The (R95)has the 1st band pretty worn off, but it may be green, then red and orange. R100 I cant really tell. Suppose to be 2.2meg. I have Sams 140, folder 9. I also have that extended lead from the output transformer to pin 2 of the output tube. Tubes checked ok. Soooo - what next?

I do plan to recap the power supply next. Tom, what diodes did you use to replace the selenium rectifiers? Just plain silicon diodes? Did you need to use any dropping resistors?

Heres a couple shots of the area in question:
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Attachment:
DSC05462.JPG
DSC05462.JPG [ 89.16 KiB | Viewed 1104 times ]

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 5:18 am 
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If it's the Standard Coil turret tuner I think it is, you can figure out which channel you are on by looking at the numbers on the channel strips, then count how many detent notches it is from the one that's in position to touch the fixed contacts. Or you can pull a bunch of them out, they are only held in by a spring pressure against the outer ends, leaving in the ones for the channel you want.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 5:50 am 
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I'll look at that tuner a little closer and see if I can tell. May have to pull the cover. Kinda need to know that I am on the right channel before I can go too far. Nothing comes in when I roll through the channels. On the resistor in doubt, it may be the 8.2k. If the 1st band is gray (cant tell for sure,) and the next is red (2) and orange (000), may have drifted up. The .047 cap had a crack in the case and test very leaky to say the least, so that may be most of the culprit. The crack was on top out of sight. Ill neat up the transformer lead and general area. Been some repairs or something, melted insulation and all.

Edit:
I was studying the circuit and noticed that there 3 sections of the 6SN7 paralleled for the output. Interesting. So I bet if one of the tubes fail, namely v24, it could take out the other as well. That may explain the heavier 6BL7 in the v24 socket.

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Last edited by TV MAN on Jan Sat 05, 2019 6:10 am, edited 2 times in total.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 5:55 am 
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Madmurdok wrote:
what diodes did you use to replace the selenium rectifiers? Just plain silicon diodes? Did you need to use any dropping resistors?
Hi Tim,

I use a 1N4007 silicon rectifier to replace all selenium rectifiers. Those are dirt cheap. The B+ is only about 6 volts higher for a silicon vs. the original selenium. That's of no consequence, and does not require any additional dropping resistor.

The voltage drop across an old selenium will be higher, even if the rectifier is unused, fresh out of the box, so if you measured B+ with an old rectifier your difference may be more. Of course, modern higher line voltages may elevate the B+ a bit more.

Also, VERY IMPORTANT...
That large black banded capacitor left of center MUST be replaced before you apply power to the set, and so must all similar caps. Those Black Beauty caps have deteriorated over the years, with much higher leakage than when they were new. They can fail catastrophically, i.e. explode.

- Leigh

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 6:06 am 
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The rectifiers would have been standard silicon diodes. Whatever Purchase Radio was selling at the time. I believe that the rectifiers were replaced at an earlier time than when I did that restoration, possibly some 45 years ago. No droping resistors were added but I did set the line voltage adjustment for the highest line voltage.

The resistor color code:
Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violate = 7
Gray = 8
White = 9

The first 2 bands are the 2 significant digits. The third band is the number or zeros to put after them. The fourth band is the tolerance. No fourth band is a 20% tolerance. Silver is 10%. Gold is 5%

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 6:13 am 
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I had the preceding post wrong for a few minutes.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 6:32 am 
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I think there may have been a 12k in the R95 position instead of the 8.2k. The 1st band may be brown. It is hard to tell since it is about rubbed off. Thanks for the reminder on the color codes. I was trying to remember lol. So, then, what is the 12k doing in there? I guess I could tack the 8.2 in there and see what I get. Use whichever seems to work the best. Found the cathode resistor on the output drifted up some also. Probably replace to be on the safe side. I am going to replace all the black beauty caps, but plan to do a section at a time - test and verify, then go to the next. C83 was cracked and leaky, could really be pulling down my vertical gain.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 6:42 am 
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Madmurdok wrote:
I am going to replace all the black beauty caps, but plan to do a section at a time - test and verify, then go to the next.
I VERY STRONGLY suggest you NOT do that.

Each time you apply power, you invite a catastrophic failure which may take out other parts. It may be difficult or impossible to find replacements at any reasonable price.

Failures happen instantly. You don't know one has happened until AFTER it has happened.

- Leigh

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 6:48 am 
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Leigh wrote:
Madmurdok wrote:
I am going to replace all the black beauty caps, but plan to do a section at a time - test and verify, then go to the next.
I VERY STRONGLY suggest you NOT do that.

Each time you apply power, you invite a catastrophic failure which may take out other parts. It may be difficult or impossible to find replacements at any reasonable price.

Failures happen instantly. You don't know one has happened until AFTER it has happened.

- Leigh

I will second that advice. The black plastic cased capacitors are for some reason much worse than the standard wax paper caps. Driving the grid of a tube positive will damage the tube. Shorting out the power supply can damage the power transformer. And those caps can explode.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sat 05, 2019 7:02 am 
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Tom Schulz wrote:
The black plastic cased capacitors are for some reason much worse than the standard wax paper caps.
Hi Tom,

The Black Beauty caps are oil-filled. That's how they got the high voltage rating in such a small package. Over time, the black plastic package develops cracks and the oil leaks out. The dry capacitor has a much lower operating voltage than the oil-filled original, and fails under power.

- Leigh

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sun 06, 2019 3:12 am 
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Point taken Leigh. I really hate to shotgun things. One thing I am doing is powering up slowly each time instead of hitting the switch at full power. I also don't run it long. I kind of like to observe and troubleshoot. But I don't want to blow something up either. At least I know what is there, and what is not. Cap time.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sun 06, 2019 3:56 am 
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Madmurdok wrote:
Point taken Leigh. I really hate to shotgun things.
Hi Tim,

Replacing caps that have a known high failure rate is not "shotgunning".

It's common sense.

Back when I started repairing old radios in the 1950s I always went through normal troubleshooting and only replaced parts that proved to be bad.

Fast forward 60+ years. Bad parts are bad parts, and my time is worth more than $0.

Think in terms of a flat tire. It's flat because the air escaped. The Black Beauty caps have exactly the same problem, except it's the oil that leaked out rather than air.

Would you drive on a flat tire?

- Leigh

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Sun 06, 2019 1:20 pm 
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If a radio or TV set is powered by a 117 VAC wall socket, the characteristics
of the line circuit become part of the radio.

Bench testing it with a Variac can conceal faults, or enable the faults to alter
other parts in such a way to change the way the radio works.

The reasoning is as tubes heat up power is supplied at a rate of rise that could
damage the cathode if a partial short circuit is encountered. If the rate of rise
is slowed or even limited, heat in (for example. coils or resistors) could change
their values. Sustained overcurrent in carbon resistors can make resistance rise.


Case 1. The rectifier burns out on full line power up. Fault finding causes the
filters to be replaced.

Case 2. The rectifier does not burn out, but causes the resistors or chokes to
overheat, to a point where, even with a faulty filter, the radio plays, but poorly
even when returned to normal line voltage.

Simplistic in the extreme,but electronics is filled with extreme puzzles.

The Telstar satellite got zapped by an unexpected event, which did not
outright kill it, but 'bent' it's logic . After a complex reprogramming functions
from earth, the nonworking gates were ignored, and it started functioning again.

In industrial electronics protection is provided for both over and under voltage .

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Mon 07, 2019 12:34 am 
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It's a waste of time to troubleshoot a pre-1965 piece of equipment without replacing ALL of the paper and molded-paper capacitors; even mica capacitors are starting to fail now.

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Mon 07, 2019 2:30 am 
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Tim Tress wrote:
It's a waste of time to troubleshoot a pre-1965 piece of equipment without replacing ALL of the paper and molded-paper capacitors; even mica capacitors are starting to fail now.


Some of us made our grubstake in radio before 1965, and are living happily off it
now.

We have all the damn time we want to troubleshoot things.. :D

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 Post subject: Re: Powering up a set with a variac - The Craftsmen RC 200 r
PostPosted: Jan Mon 07, 2019 2:50 am 
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Thanks guys! Probably is a waste of time to troubleshoot before the full recap. However, I wanted to do it in sections in case I screwed something up, but now knowing the reputation of the black beauty caps, they will go. I do monitor the current pretty close, but if powering it up slowly is bad, then that too will go. I don't want to cause a problem by replacing something, but I guess if I do, then I can troubleshoot lol. I guess it used regular wax caps, then I could do a section at a time, test then go on. It is my first attempt restore a TV via a recap, etc. I had only done repairs previously, so it is engrained pretty deep.

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