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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Mon 14, 2017 7:51 pm 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 913
Location: Wyoming, Michigan
Radio meets still have tube testers, and usually a fair crowd of knowledgeable folk who have at least some experience on TV sets. A lot of common ground.

Posting entire Sams folders here would probably not be liked, but snippets of schematics, relevant to discussion, are always welcome. Example I just posted:
viewtopic.php?f=3&t=325749&p=2727010#p2727010

Forum restraints on image sizes can be coped with using tools like shrinkpictures.com.


You're doing fine so far.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Mon 14, 2017 7:56 pm 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
Here's some stuff to look at in the meantime:

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One thing I enjoy about buying tubes is sometimes you never know what you'll get. I've read RadioShack was still honoring the lifetime warranty on its Realistic tubes up until a few years ago. Manufactured in "Gt. Britain", it's probably a Mullard, no? I love the artwork on the boxes.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Mon 14, 2017 9:58 pm 
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Joined: Aug Thu 12, 2010 6:25 pm
Posts: 167
Location: Durham, NC
I love seeing that ultrasonic remote in such nice condition. I've started gathering info about remote controls for an article or two on them in the AWA Journal (I'm the TV columnist). Do you know how the circuit works? Does the "On/Off/Volume" button just cycle through On, a few volume settings, then Off, or is there some hold-the-button-down action involved? With only one button, putting that many actions together is an interesting engineering challenge.

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Mark Nelson
A collector of TV signal boosters and UHF converters -- God help me!
tv-boxes.com


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Mon 14, 2017 11:40 pm 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 913
Location: Wyoming, Michigan
NelsonM wrote:
...Manufactured in "Gt. Britain", it's probably a Mullard, no?


This link will help you:
http://www.effectrode.com/tube-enthusaist-tube-codes/


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Tue 15, 2017 2:14 am 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
aj2x wrote:
I love seeing that ultrasonic remote in such nice condition. I've started gathering info about remote controls for an article or two on them in the AWA Journal (I'm the TV columnist). Do you know how the circuit works? Does the "On/Off/Volume" button just cycle through On, a few volume settings, then Off, or is there some hold-the-button-down action involved? With only one button, putting that many actions together is an interesting engineering challenge.


I'm curious about that myself. I don't know how it works yet. It takes a 4V mercury cell that's NLA. Three 1.5V button cells in series seems to be the alternative. Hopefully, I will be able to demonstrate its function soon in a video.

Unfortunately there's no such code on the tube. There's "GT BRITAIN" and the tube type in white print on the glass; then there's the Lifetime logo, "BRITAIN", and the tube type again in yellow on the glass.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Tue 15, 2017 2:47 am 
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Joined: Jul Wed 08, 2009 12:17 am
Posts: 913
Location: Wyoming, Michigan
I would suggest the tube codes are there. They can be extremely faint, and are easy to overlook. I've never seen a British tube without one, but perhaps you have a counterexample. It wouldn't be accepted by a collector as authentic without the proper codes. But collectors probably wouldn't collect TV tubes anyway so it's probably moot. Just academic and only if you care.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Tue 15, 2017 4:40 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
NelsonM wrote:
Thanks for the info. I will look into a recap. From what I've found, there are more radio meets and clubs than there are TV ones around here. There's an old electronics service shop around the block from me that's been around since 1953 still advertising TV and radio parts and repairs on a faded hand painted sign in the window. The owner basically shooed me away, informing me they stopped servicing TVs and sold off their stuff nearly 20 years ago. He couldn't even tell me where I could find resistors and capacitors locally. That's the state of the hobby here in NYC, not even the army of bearded vintage gear head hipsters can spark its resurgence.

It's been scary constantly reading and hearing how important it is to determine the health of the CRT before doing any work and the difficulty in finding replacements. After all the assurances, I won't be so quick to give up on this thing. Thanks again to everyone.


I'm in a local radio club and it seems like a little less than ten percent of the active members are interested in TV, so don't write off a local radio club. Present modern electronics repair is a much different business than it was back in the '50s and '60s. There are a few people on these forums that are former TV repairmen. Some here do restorations and might turn a small profit, but most are doing this as a hobby. A hobby doesn't usually doesn't make sense economically. Some here are working on a single set like yourself, others might have dozens of TV and have to manage their time . Whether an item is "worth it" depends on many factors. You set has a stable picture with good contrast, so much of the set including the CRT is working OK. It has a number of problems, some of which might have a common source. With this good a picture you will be able to see improvements as you go along. Except for the RF/IF alignment, which is involved and requires special test equipment, don't be to afraid of trying the adjustments. Because parts have a tolerance on their value, when you replace parts adjustments could be required anyway. I am on this forum as well as Video Karma, which specializes more on TVs.

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Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Fri 18, 2017 8:33 pm 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
Got it, I'll try to find a local club meet.

I went ahead with the advice to clean the sockets and, to my amazement, most of the tubes that I pulled looked bad. I distinctly remember pulling, inspecting, and wiping down each of the tubes not long after I acquired the set in November and I found them to be acceptable. However, now I see most of them have some degree of blackened getter and even darkened glass. It's entirely possible I didn't know what I was looking at before, but is there any reason that pretty much an entire set of tubes can go bad after putting maybe 1 hour on it? Is there any problem that could cause a cascading failure? Maybe the gentle rocking motion to remove them for the previous cleaning broke the vacuum seals? I wouldn't want to put a new set in just to have it happen again.

If someone has the following tubes for sale, please contact me:

8FQ7 H. mult - silver/milky getter (maybe still good)
13GF7 V. mult/V. out - silver/dark/milky getter
4HS8 Sync sep/AGC keying/Noise canceller - silver getter with black spot
11KV8 Video output/Sound IF - silver getter with black spot
4EH7 1st video IF - uniform black getter
4EJ7 2nd video IF - uniform dark getter
17BF11 Audio out - silver/dark getter, darkened glass

3GK5 RF amp - acceptable
5LJ8 Mixer osc - acceptable


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Fri 18, 2017 10:00 pm 
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Joined: Sep Fri 07, 2007 2:27 am
Posts: 5131
Location: Grand Chute, Wisconsin
NelsonM wrote:
I went ahead with the advice to clean the sockets and, to my amazement, most of the tubes that I pulled looked bad. I distinctly remember pulling, inspecting, and wiping down each of the tubes not long after I acquired the set in November and I found them to be acceptable. However, now I see most of them have some degree of blackened getter and even darkened glass.
In most instances you can't tell if a tube is good or bad merely by looking at them. Getters should be silvery/black. White, dusty, and flaky is usually bad. But that test only tells you if a tube has "gone to air". All other tests need to be done with a good tester or by using in a known good radio or TV.

.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Fri 18, 2017 10:07 pm 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
Ok. I'm just going to try powering it on tonight to see what happens. Looks like I'll have to expedite this club search.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Fri 18, 2017 10:09 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 672
Location: Pewaukee, WI
The geter inside the glass is supposed to be black, or silver. If the geter turns powdery white that is when the vacuum has been compromised.

Your tubes are probably just fine. (It is possible for good looking ones to be weak or have heater-cathode shorts and the like, though...So test them)

EDIT: missed seeing Jim's advice before posting.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Aug Fri 18, 2017 10:14 pm 
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Joined: Sep Fri 07, 2007 2:27 am
Posts: 5131
Location: Grand Chute, Wisconsin
NelsonM wrote:
Ok. I'm just going to try powering it on tonight to see what happens.




Image



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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Thu 25, 2018 8:10 am 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
Ok so I'm finally back from turning it on :lol:

https://youtu.be/45PWv4-oUes

The picture is acceptable, but there is a strong hum/buzz in the audio. I have the following setup:

HDMI output -> HDMI to RCA converter -> RF Modulator -> balun -> VHF

Looking about has caused me to wonder:
- AGC fault?
- Possible demodulation or tuner alignment issue?
- Overmodulation? Would an attenuator solve this?
- Ground loop isolator? Unplugging the audio and leaving the video line in doesn't stop the buzzing.

No luck contacting local radio clubs...


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Thu 25, 2018 8:38 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 281
Does the buzz stop when you disconnect the video? See my post about playing copy protected content on vintage TVs.

If disconnecting the video stops the buzz, try reducing the video level a little into the modulator - there may be an adjustment in the modulator for that. If not, shunt the video line with a 200 ohm pot and adjust it.

You may be able to improve matters with the TV's fine tuning control. If that doesn't help, and after you've checked everything else, the TV's sound IF and demodulator may need alignment. DO NOT adjust anything though unless you can correctly identify the coil / transformer and NEVER adjust anything in the vision IF.

I'll need to look at the schematic to give you more advice on this. You'll need the proper tools or you'll break slugs inside coil formers - bad news. Whatever you do just don't go poking around with these things.

Another thing, no matter what anyone tells you, that set is too new to need recapping. Don't even think about it!

I just had a look at your video. It looks like the video level into your modulator is too high, there is white crushing in the image.

Also, do you get a white spot when switching off? Check that the CRT dag coating is grounded - there should be a long spring or spring loaded wire across the graphite coating, connected to ground. That might also affect the sound.

One last check just occurred to me - is the hum / buzz still there with the volume at zero? If so, ignore for now what I've said and look for an open circuit B+ filter capacitor in the audio output circuit.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Thu 25, 2018 11:57 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 281
I was in the office when I looked at your youtube video. I since had a chance to listen to the rest of it, at home.

Yes, definitely, your video level into the modulator is much too high. That's your problem. Try the 200 ohm pot as I suggested earlier.

Or you have a really crap modulator....


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Thu 25, 2018 8:08 pm 
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Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
Thanks irob2345, I'll try the pot before tinkering with the alignment.

As for the RF modulator, it's an RCA... the badge of quality :lol:

Image


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Thu 25, 2018 9:55 pm 
Member

Joined: May Sun 07, 2017 11:35 am
Posts: 281
It could also be that the output from your HDMI to CVBS converter is too hot. Digital designers often don't understand analog!

Crack the case of the modulator open. There might be a pot for video modulation level in there. You should adjust it so the peak white from menus displayed by your box doesn't result in hum.

Do read my post on this subject....

viewtopic.php?f=3&t=332446


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Fri 26, 2018 3:42 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I've used modulators like that and didn't have a problem. Probably the video input is too high.

_________________
Tim
It's not the Destination, It's the Journey.


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 Post subject: Re: Sears Silvertone Medalist All Channel
PostPosted: Jan Sun 28, 2018 6:36 am 
Member

Joined: Dec Mon 14, 2015 7:54 am
Posts: 25
Location: New York City
You're amazing.

I took apart the modulator and found a pot. A bit of a twist and the buzz is gone!

The focus and the picture adjustment can use a little tweak, but I can finally put the chassis screws back in on this now two year old project and put the finishing touches on it.

Onto the next challenge... the remote.

Thanks to everyone still here for making this possible.


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