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Old 1st Oct 2017, 6:16 am   #1
ct92404
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Default My first antique TV-Olympic Model 755-need help.

I just bought my first antique tv yesterday

It's an Olympic Model 755, made in 1951 or 1952 I think. I have never actually seen a tv this old in person before! And now I own one, so I'm really excited and anxious to hopefully get it working again.

It powers up, the vacuum tubes glow, and the cathode ray tube lights up. There are flickering horizontal lines going across the screen, and there is a loud buzzing and humming sound coming from the speaker. So I'm pretty sure there must be some bad filter capacitors. The screen does respond to the brightness control, and I think the CRT itself is working. At least I know the high voltage supply is working and the screen seems to be scanning. But maybe AC line noise is driving it nuts because of bad filter caps?

I assume my first step should be to replace electrolytic filter capacitors. The problem I'm having right now is that I can't find a schematic. Actually, I'm having a hard time find any information about this tv. I couldn't even find a diagram on RadioMuseum.org. So I'm pretty much stuck right now. Does anyone know where I might be able to find a diagram? I'd also appreciate any other help or suggestions for what my first things to check should be. I have some experience fixing old vacuum tube radios, but I have never worked on an antique tv before!

I'm in the US, but I've had a lot of help from people on this site before.

- Chris
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Old 1st Oct 2017, 7:53 am   #2
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Default Re: My first antique tv - need help

Hi Chris

I see on "Sams PhotoFact" advert on eBay.com TV OLYMPIC MODELS 752 U 753 U 755 U 764 U & 767 U complete service manual is available. The advert says it is yours for $4 plus p&p.

The downside is that the photo shows a different model so check with the vendor before parting with those hard earned dollars!

Chris nee Simpsons
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Old 1st Oct 2017, 9:12 am   #3
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Default Re: My first antique TV-Olympic Model 755-need help.

Your TV model is not noted but this web page has some Sams and Rider manuals for Olympic TVís.
http://www.earlytelevision.org/tv_sc...p.html#olympic

May be some similarities in the chassis used if you cannot find anything nearer to your TV.
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Old 1st Oct 2017, 9:39 am   #4
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Default Re: My first antique TV-Olympic Model 755-need help.

Hi Chris,
I'm sure we would all be very interested to see some pictures: after all, we don't get to see American TV's very often!!
Were American sets of that period designed for AC/DC mains and therefore 'live chassis' or did they have mains transformers? Thinking about it, if they were designed to operate from 110v, it would not be possible to get enough HT (usually 200V or so) with UK type design. I imagine, therefore, they were for AC only and will have a transformer. I would be interested to know!
Outside of New York, I don't know if DC mains was still in use in the 1950's in certain areas.
All the best
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Old 1st Oct 2017, 10:36 am   #5
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Default Re: My first antique TV-Olympic Model 755-need help.

Hi Nick,
There were transformerless designs but not AC/DC, Sylvania used them and some portable sets.
Various references in the magazine Radio-Electronics from the early 1960’s.
This page from http://www.americanradiohistory.com/...cs-1964-02.pdf
Apologies the screenshot is a bit blurred but the download from American radio is clear.
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Old 1st Oct 2017, 11:27 am   #6
ct92404
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Default Re: My first antique TV-Olympic Model 755-need help.

I think I found diagrams!

I Googled the models that were listed in the PhotoFact manual that Chris Simpson mentioned. I figured they must use the same chassis as my tv. I found a PDF file with a manual for a bunch of different tvs:

http://www.americanradiohistory.com/...an-1952-TV.pdf

The diagram for my tv is on pages 107-110. I'm still looking at it right now to try to make sense of it. I really hope the problem is just the filter capacitors. I hope I'm not getting in over my head!

Nick,
I'm going to post some pictures soon. I just finished cleaning the chassis and cabinet yesterday - it was filthy with probably decades of dust! It's looking a lot better now, and everything seems to be in pretty good condition.

I honestly don't know much about how tvs were wired back then. This tv does specifically say AC 60hz for the power though. Old radios on the other hand have the tubes connected in series, so they didn't need a transformer.
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Old 1st Oct 2017, 11:58 am   #7
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Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by ct92404 View Post
I really hope the problem is just the filter capacitors. I hope I'm not getting in over my head!
If you go over some old TV threads on this site you will find that we need to change more than just the 'filter capacitors'. You may not be familiar with some of our terminology and engineer 'slang'. You probably know that we call tubes 'valves'. We tend to call filter capacitors 'HT smoothing' (HT is our term for 'B+'). 'Caps' is a shortened form of 'capacitor'. You will also see 'waxies' which is what we tend to call the old wax covered paper capacitors that are basically now 'change on sight' components.

You will probably find that most, if not all the old paper capacitors (waxies) in your set will need changing and of course the filter capacitors although sometimes these can be 'reformed' to work satisfactorily.

Quote:
Originally Posted by ct92404 View Post
I honestly don't know much about how tvs were wired back then.
Well if you can post part or all of the circuit, we can certainly help talk you through it. Fortunately most of the circuitry should be familiar to us.

Watch out for our different terms though! What you call a 'sweep tube' to us is a 'line output valve'.
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Old 1st Oct 2017, 12:16 pm   #8
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Default Re: My first antique TV-Olympic Model 755-need help.

It uses a conventional mains transformer and parallel valve (tube) heaters, full wave rectifier.
A turret tuner for I presume 12 Channels using a Pentode for RF and and a double triode for the mixer/osc. IF in the 25 MHz region with a seperate IF of around 21Mhz for sound, this does not use intercarrier sound. Looks like a Foster Seely FM detector.

I like the socket marked “ Color Converter socket!

Edit. Just noticed the use of the sound output valve as a HT supply to various stages,400 volts on its anode and 140v on its cathode, suitably smoothed to provide a lower voltage HT for IF stages etc.
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Old 1st Oct 2017, 12:40 pm   #9
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Default Re: My first antique TV-Olympic Model 755-need help.

You appear to have a raster from what you've written, but have you actually tried it with a signal yet? I presume that like here you will not have any analog(ue) transmissions available any more so you will need a signal source (set top box/VCR etc) and a VHF modulator to receive anything.

I would try and get a picture on the screen, then replace any suspect capacitors, but do these one at a time and check the results after each replacement, then you will know if theres a problem it will be the component you replaced last.
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Old 1st Oct 2017, 12:56 pm   #10
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Default Re: My first antique TV-Olympic Model 755-need help.

I seem to remember they were giving vouchers for digital set top boxes with a suitable VHF output, may be able to find one cheap or free.
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Old 1st Oct 2017, 1:10 pm   #11
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Default Re: My first antique TV-Olympic Model 755-need help.

Being based in the US myself: the digital switchover happened quite a long time ago now. By 2009, they had stopped handing out the coupons to get free or reduced-price digital boxes.

To obtain a box now, enter "ATSC tuner" or "ATSC converter" into Amazon and numerous choices will appear, starting at around $30.

Having said that, in the US an old-telly restorer has the advantage that the 525-line NTSC analogue service stayed in effect all the way until the digital transition. Because of this:

--Any US VCR or DVD player that has an RF output should work fine as a source.

--AFAIK most set-top boxes provided by cable companies still have an RF NTSC output (along with RGB analogue outputs and digital outputs). Thus Americans who don't yet have modern TVs can still watch their cable channels. I added AFAIK to the front of this paragraph because I don't personally have cable TV. I actually use an ATSC tuner, connected to an indoor UHF antenna, which works quite well in my reception area. The tuner has both digital outputs and analogue ones, including an old-fashioned RF NTSC output.

--One of the pecularities of the US switchover to digital is the numbering of the channels. In practice, most of the digital stations use UHF, but they continue to use the old channel numbers on the LCD display on the front of the tuner. This is because for US stations, the old VHF channel number is so much part of their "identity." Thus for instance, my local CBS-owned station is shown as Channel 4 on the front of the tuner, but is actually broadcasting on UHF Channel 30.
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Old 1st Oct 2017, 4:50 pm   #12
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Default Re: My first antique TV-Olympic Model 755-need help.

Quote:
Originally Posted by Clydeuk View Post
You appear to have a raster from what you've written, but have you actually tried it with a signal yet? I presume that like here you will not have any analog(ue) transmissions available any more so you will need a signal source (set top box/VCR etc) and a VHF modulator to receive anything.

I would try and get a picture on the screen, then replace any suspect capacitors, but do these one at a time and check the results after each replacement, then you will know if theres a problem it will be the component you replaced last.
Most of the US, old TV collectors websites always warn about trying old sets before restoration. I'm in this hobby for several years now and the only way to tell the extent of repairs needed is to try it. OF course, my first tryout is to use a series lamp limiter to detect a real serious in the power supply.
Then, I use a signal source after seeing somekind of an image on the screen. My restorations are always done in stages.
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Old 2nd Oct 2017, 12:42 am   #13
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Default Re: My first antique TV-Olympic Model 755-need help.

I'm planning to replace capacitors C50 and C51 first. Actually, they're both in a combined "can." I've noticed that seemed to be common in the 1950's and 60's, where two or more electrolytic filter capacitors were put together in one unit. I guess it was just to save space. According to the schematic, C50 and C51 are connected to a 5U4G rectifier tube. There's a loud hum and buzzing on the speaker that doesn't respond to the volume control. That's exactly the same behavior I've noticed on antique tube radios when the filter capacitors are bad. On my radios, as soon as I replaced the caps, that always fixed the problem. So that's why I'm suspecting that the filter caps are the main problem with the tv. It sounds like the same loud buzzing from the AC line. I know it might not be the only problem, but I sure hope it's the only major one!

There's also another capacitor in that "can," C15. (On page 110). So in total I'm going to have to replace 3 capacitors when I take out that one unit. I really wish they hadn't put capacitors together like that! I understand they probably did it to save cost and space, but it makes things a royal pain now!

I'm attaching a few pictures. I have the tv taken apart right now. Believe it or not, the chassis looks a lot better than when I first got the tv! It was completely covered in dirt and dust before!

I tried to get a picture of the screen with the tv on. There are flickering horizontal lines, which hopefully you can see in the picture. It looks brighter than in the picture though. The fact that the lines look fairly clear even in the daytime and the screen does respond to the brightness control is hopefully a good sign that the tube is still good. I'm suspecting that the wild flickering is caused by bad filter capacitors (C50 and C51). Since that supplies DC power to everything else, I would think that AC rippling would cause problems everywhere.

This is the biggest repair project I've ever done, so I'm just going to have to take this a little at a time!

- Chris
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Old 2nd Oct 2017, 9:09 am   #14
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Default Re: My first antique TV-Olympic Model 755-need help.

Multiple electrolytics in one can were common, replacements were easily available it was standard practice. I donít think the designers would expect or even care about serviceability 65 years later.

Looks a nice TV, the capacitors being bad is a good assumption, they may reform but if you have replacements they may as well be changed.

Itís possible with some electrolytic cans to restuffed with new ones if you want to keep it looking original. Search this forum for suggestions and instructions.
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Old 2nd Oct 2017, 4:45 pm   #15
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Default Re: My first antique TV-Olympic Model 755-need help.

That picture on your screen might not look much, but it means that everything in your set, from the antenna jack to the CRT is working after a fashion.

Smoothing cans, as we call them are not a big deal, if you don't want to re-stuff the originals you can do what I did when I restored my Cossor TV of similar vintage to yours, and find an empty can of similar diameter and stuff it with modern electrolytics which fortunately are physically a lot smaller than the vintage ones for a given capacitance/voltage rating.
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Old 3rd Oct 2017, 9:51 pm   #16
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Default Re: My first antique TV-Olympic Model 755-need help.

Hi Frank,
Many thanks for posting the link to the magazine. I ended up reading quite a bit of it! With 110V mains, I guess they had the opposite problem to us so had to either use a transformer or voltage doubling circuits. This must have lead to sets running much cooler then their British counterparts.
Certainly the article showed one power supply arrangement where one side of the mains went to chassis. With American plug/ socket design, it would not have been possible to ensure that the chassis was neutral
Hi Chris,
Nice to see some pictures. Interesting to see a light coloured cabinet: the fashion with most UK sets of the time was very dark brown. That's also a very square cornered CRT- what screen size is it? Any chance of some under- chassis shots?
Good luck with the restoration,
All the best
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Old 4th Oct 2017, 8:28 am   #17
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Default Re: My first antique TV-Olympic Model 755-need help.

Unfortunately, I had a major setback tonight.

I replaced the filter capacitors - C50, C51, and C15. The wiring was really confusing though, and I had kind of a hard time matching it up with the diagram. The most confusing thing is another capacitor, which seems to be C16 according to the diagram, but the actual capacitor has a different value. I'll explain that in a minute. Eventually I was pretty sure I had everything connected right, and I tried to test the tv again. At first, I noticed what seemed to be an immediate improvement from before. Instead of just flickering horizontal lines, I actually got more of a uniform glow on the screen, and it even responded to the horizontal and vertical controls. There was still some flickering, but much less than before.

But then things started to get weird...the "image" on the screen started to shift progressively towards the right and I thought I started smelling something kind of strange. Then I heard a bubbling and hissing sound! I quickly turned off the tv and unplugged it. I checked under the chassis and it looks like that other capacitor (C16?) had ruptured. I couldn't see any obvious breaks on its casing, but there was a dark brown pasty stuff nearby where it seemed to have leaked. The new capacitors on the other hand seemed to be fine, so apparently I DID connect them right.

Here is where things really get confusing. I don't know why that capacitor has a different value than what's indicated on the schematic for C16. Maybe someone had replaced it before? Maybe the company decided to use a different capacitor than the original design? But I'm positive it has to be C16, because the positive side of if connects to one of the lines on the audio transformer, just like what's shown on the schematic. The other big problem is I really don't understand why it apparently burned and ruptured like that. I connected it the way it's shown in the diagram, as best as I could figure out.

The most confusing thing is that I don't see how it would even be possible to connect C16 the way it's shown in the diagram. If anyone has a chance to look at the schematic at the link I posted before, please look at page 110. You'll see a schematic on the left side of the page, showing how C15 and C16 are connected. I replaced C15 (and it seems to be ok), but I think C16 is the cap that blew. The negative side of it connects to the POSITIVE side of C15 and pin 8 of the 6v6 tube. How is that even possible?? How is the negative side of it supposed to connect to the positive side of C15?
It almost looks like they're connected in series, but I don't see how you can do that with an electrolytic capacitor.

I'm really stuck right now. I feel like I could be making some progress, if only I could figure out how that capacitor is supposed to be connected. I have the tv outside on a table in the back yard. (I don't have any room in the house to work on it!) It's too late for me to do anything else with it tonight. But if it would help, tomorrow I can check the actual value of the capacitor that I think is supposed to be C16.

If anyone can figure out what I'm doing wrong, please let me know!

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Old 4th Oct 2017, 9:09 am   #18
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Default Re: My first antique TV-Olympic Model 755-need help.

The power supply arrangements for the output valve are a bit odd to my way of thinking, but they are valid. There's 380V on the anode and 140V on the cathode.

C15 has 140V across it with the correct polarity.

C16 has 380-140=240V across it with the correct polarity.
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Old 4th Oct 2017, 9:32 am   #19
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Default Re: My first antique TV-Olympic Model 755-need help.

Electrolytic capacitors can be connected in series, that's not unusual in high voltage power supplies, it's a way of reducing the rated voltage needed if a single capacitor was used.

In the schematic they appear to be connected correctly...C16's +ve to 380v +ve line, C16's -ve to 140v +ve line, C15's +ve to 140v +ve line, C15's -ve to chassis....Look at it from the point of view that C16 and C15 in series present a total value of just over 25uF across the 380v HT line and filter that line and that C15 presents itself as written on the schematic eg: 60uF and that it filters the 140v line.

Also it might help you to view the sound output stage (6v6g) as operating with a differential HT voltage, eg: anode to cathode voltage is the difference between the 380v line and the 140v line, that way the grid bias arrangement will make sense etc.

Not sure where the 140v line comes from yet as I can't seem to trace it back to its source, maybe part of the schematic is missing?

EDIT.....Post crossed.

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Old 4th Oct 2017, 10:35 am   #20
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Default Re: My first antique TV-Olympic Model 755-need help.

Ignore last sentence in my last post...wasn't thinking!

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