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 Post subject: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 1:48 am 
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Location: Bridgeport, OH
I just found this set and it will be my first tv I’ll work on. I brought it up on a 75w light bulb and I think I am getting no high voltage. All the tubes were illuminated and I was getting some noise out of the speaker when moving the volume. The volume went away only a few minutes later. I also tried plugging it in without the bulb for a short time and got nothing but tube illumination. I am not sure if a breaker exists for the high voltage or other common problems cause the audio to go away and not giving high voltage.

The set appears to not been worked on that much besides the volume control, it appears to have been replaced.

I am unsure if I have to buy the schematic straight from sams or if a resource like nostalgia air exists for tv’s.

I have worked on a few tubes radios so I know some basics.

Thanks for the help!


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 2:49 am 
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Location: Bridgeport, OH
I do not have a tube tester but was able to figure out what tube this is. The filament appears to be good but it is not illuminating.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 3:24 am 
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Location: Southwestern,Ontario Canada
Hello, It is going to be very hard to be able to see the filament glow of a high voltage rectifier tube. Other tubes yes, just not that one. Have you done a modest recap of the high voltage circuits. horizontal, vertical ?
Tony


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 5:55 am 
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Location: Bridgeport, OH
I haven’t done anything to the set yet. I realized a reset switch was stuck pressed down. After moving it back the audio and a picture came up. Just need to get the schematic to do a recap. Still do not know if I need to buy directly from sams or if a site like nostalgia air exists for tv schematics.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 8:34 am 
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Joined: Jan Thu 16, 2020 12:29 am
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It is actually not a wonderful idea to power these vintage sets, even with a light bulb limiter or a Variac. The problem is the person with them gets enthusiastic and interested to see if they might be working and the temptation to power them is just too much for some to resist. The curiosity to see if they will work is a powerful force. I see this all the time with predictable results.

However, it is highly likely that most of the wax paper capacitors will be electrically leaky. This can put positive voltages on the tube grids, which is a bad thing for tubes like the horizontal output tube (& the transformer it is connected to) and the audio output tube. In addition, the electrolytic caps in the power supply and any cathode bypass applications will likely have gone low capacity, high ESR and or electrically and possibly physically leaky. There will be high ripple levels on the HT supply rails.

Abnormal or high value resistors cause less issues and can be detected and replaced later. The same applies to the mica & ceramic capacitors.

So the reality is, to be safe and get a TV set, so that when you "switch it on" there are a minimal number of faults to track down, the wax paper caps and electrolytic caps should be replaced, especially if they are over 50 years old.

Or, you can take shortcuts, and attempt an initial one by one fault track down, but you will be presented with a plethora of multiple faults and possible damage to tubes & transformers. Sorry to be the bearer of news that indicates quite a lot of work needs to be done first, and restraint needs to be shown, before powering an original untouched vintage television set.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 10:34 am 
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Location: Belrose, NSW, Australia
Yes Hugo I strongly concur. Too much damage can be done to parts that are made of unobtainium!.

However, if the set is sort of running, there is something to be said for just replacing the critical caps - grid couplers to hor OP, vertical OP and audio OP. Then, take lots of pictures and replace caps a few at a time, testing in between. That way, if you make an error, it is MUCH easier to find.

Unless you are confident you can do the whole chassis without making a single error, that is. Wiring errors can be VERY hard to find.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 1:11 pm 
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irob2345 wrote:
Unless you are confident you can do the whole chassis without making a single error, that is. Wiring errors can be VERY hard to find.


Yes that is true and likely harder to find for those who made the wiring errors in the first instance.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 3:29 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 531
Location: New Hampshire
If you buy a "new" Sams it will be a crappy PDF or Xerox & cost you $22.
Try to find the original high quality paper Sams & save $$.
There are a few places that sell them. I also sell them but mine only go back
to abt 1968. It would be $8 from me if I had it.

good luck
Zeno
LFOD !


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 7:03 pm 
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You can find some Admiral schematics here http://www.earlytelevision.org/tv_schematic_diagrams_admiral.html. But I don't see any listings for anything like the model number you show. Do you know what Sams it would be in? With the Sams folder number you could browse that link for that Sams.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 8:20 pm 
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Location: 07450, New Jersey
Sams index says it is covered in 758-1.

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Tim

"One of the advantages of being disorderly is that one is constantly making exciting discoveries." A. A. Milne


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Sun 26, 2020 8:23 pm 
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Tim wrote:
Sams index says it is covered in 758-1.

OK, the museum does not have that one.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Mon 27, 2020 12:36 am 
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Location: Bridgeport, OH
I was able to find this link: https://www.americanradiohistory.com/Ar ... KOLf7q1joY

This appears to contain the set I have... I have done a few recaps before and will probably try to do one on this set if I found the right schematic. I am not seeing a parts list from that link so I guess I am going to have to check them all by hand.

Also I am trying to date this set.... The tubes appeared to be dated for 1964 so I will assume it is from 64'.

I will give updates if I need more help for my first set. Thanks!


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Mon 27, 2020 3:32 am 
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The Beitman's Manual that you have (I didn't know the American Radio History site had those -- a good resource!) indicates it's from 1965, so it is likely your set was made in '64 (not that its manufacturing date is terribly important). Since it's a series string set, you will probably need an isolation transformer to make it safer to work on, once you get it recapped and resistors replaced as needed. If you have an isolation transformer from radio servicing, check that it's capable of handling the higher wattage of the TV.

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A collector of TV signal boosters and UHF converters -- God help me!
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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Tue 28, 2020 3:25 am 
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Location: Bridgeport, OH
I remembered for the short time I had a picture on the tube it was a solid grey color instead of snow. The horizontal and vertical was steady but I only had it on for less than a minute. I didn’t have any antennas attached nor did I move the vhf or uhf tuner while it was on. Not sure if I should have had snow or not.

I am going to avoid powering it up as much as possible. I do not have a lot of equipment to diagnose so I am seeing if anything major could be wrong before I figure out a recap.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Tue 28, 2020 5:04 pm 
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Location: Pewaukee, WI
Some sets get snow with no signal others don't...the ones that don't usually either have a weak RF/IF tube or were not designed to work in fringe/near-fringe reception zones.

Tuners also can get dirty contacts and not pass signal till cleaned.... germanium video detector diodes sometimes die too (set will usually pass weak sound and blank raster if detector fail).


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Wed 29, 2020 12:54 am 
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Location: Dallas, TX
It sounds like the CRT is good enough. Since this set doesn't have a power transformer I think you are good to go on the major parts you can check before hand. There could be a number of problems but most of them would be hard to find before you re-cap the set, so go ahead and re-cap.

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


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Jan Fri 31, 2020 7:06 pm 
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Just how bright was the raster? Personally, I wouldn't sink a dime into that set unless I was reasonably assured that the CRT was functional.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 2:11 am 
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Location: Bridgeport, OH
I got snow but the tuner is very dirty. And the raster appears fairly bright to me. I want to pull the chassis to clean it and see what caps I need. I understand to fully remove the chassis I must remove the HV cup off the crt, but I’ve never done this. I see tutorials online for more modern sets but Idk if a good technique exist for older sets... or if I should take the cup off at all.

Also I guess the only way to I am going to find what caps to replace is physically checking each one. I see the sams is $22 but I don’t know if I’m going to pay that for just one.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 2:59 am 
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To safely remove the anode from the CRT ("HV Cup"), connect one end of an alligator clip lead to the appropriate chassis ground, and the other end onto the metal shank of a slotted tip screwdriver. Now, grasping the screwdriver's insulated handle, gently poke the slotted tip of the screwdriver under the rubber cup until contact is made with the anode.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 3:26 am 
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Location: Belrose, NSW, Australia
The raster appearing for a minute or so indicates the B+Boost cap (two of these if there is a linearity coil) has failed. That's what normally happens when you fire up an old TV. It is connected from B+ to the bottom of the flyback transformer and is normally about .047uF, 600 or 1000 volt rated. It will be a wax paper part.

Unless you are a VERY experienced and methodical operator, I strongly suggest replacing ALL wax paper caps a few at a time, testing in between, and starting with the critical ones I have mentioned. You will need the schematic for this.

You may well find that's all you'll need to do to make the TV operational.

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