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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 3:53 am 
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Location: Bridgeport, OH
I don’t think I’ll need to remove the HV cup but I might if I need the room. I have a converter box and was able to get a picture. But moving the horizontal or vertical hold the picture would get a bit jiggery. From what I understand that’s from bad caps but I am unsure. The picture seems pretty bright to me so I’ll go ahead and try a recap on the chassis.

I believe I have accounted for every cap on the chassis but two under the chassis. I am unsure if they are critical but I may just have to leave them.

Also some caps are rated for 1000v. I normal replace all of them with 600v caps. I wouldn’t think I’d need to get 1000v caps but I am unsure if 600v is able to cut it for those.

The final thing is there anything in the vhf tuner I would need to replace or is it normally fine left alone. The picture I got wasn’t great but was there... I didn’t try it for very long.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 4:54 am 
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Location: Belrose, NSW, Australia
They are normally 1000v caps for a good reason. If the manufacturer could get away with cheaper 600v caps he would have!

Those two white caps in the picture look like they might be plastic sleeved paper types. Are they the 1000v parts? If so, they will be the B+boost caps and WILL need to be replaced.

Your tuner does not have paper caps in it so you can probably leave it alone, apart form cleaning the contacts. Silver polish is good for this. Don't spray contact cleaner or CRC-like sprays into it, they de-tune everything!

About the only parts that commonly fail in this vintage of tuner are two resistors that bias the RF amp. They are usually about 1m and 820k. So if you have a weak, snowy picture, you should test these.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 5:19 am 
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I’ll replace the 1000v caps with 1600v. The two caps together in that picture are the only ones I can’t tell what the value is without cutting them out. I do not want to get confused by cutting them out now and possibly adding new ones in wrong... I’ll try to replace them when Im done replacing everything else.

I don’t know if I’d describe the snow as weak but here’s a picture I took when I had it on.... it’s not that great But the tuner still seems very dirty. I would have sprayed contact cleaner so thanks for the heads up! I’ll only use it on the pots if that’s safe to do.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 5:54 am 
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Location: Belrose, NSW, Australia
Yes 1600 volts sounds safer.

Hmmm. That doesn't really look like snow from the pic. and you have no hor. sync. Let's see how it goes when you finish the re-cap.

But at least the CRT looks reasonable, as far as I can tell.

I hope you are using an isolation transformer! If you suddenly stopped posting I might suspect you aren't! :(
And I'm too far away to call the ambulance!

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 6:00 am 
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Blustar1 wrote:
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.

Hold it in contact for about 5 seconds. Sometimes it can partially recharge if you don't hold for a few seconds.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 6:07 am 
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Only one other problem that I can see. The vhf terminal as you can see was broken off. I tried to reconnect the original right wire back to the terminal but it broke off... so I connected directly to the wire to the right. Not sure if that’s alright to do or not.

Yeah the picture I took wasn’t that great but I was able to get a DVD player to semi work on it. When I’d try to adjust some of the pots it would get jiggery. No I’m not using a isolation transformer... I know this is some risky business but I’m not turning the set back on until the recap is in order :roll:


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 4:36 pm 
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You better glue on some sort of support for the broken board or you will just rip off the wire on the other side.When working on RF circuits adding longer wire is generally not a good idea. Remember you aren't working on a Mack truck, things like cardboard and plastic get brittle with time.
Beside the capacitors being replaced and cleaning the tuner, many times things like the adjustment pots need to be cleaned.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 5:06 pm 
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I’ll try to shorten the wire if I can. But I’m noticing that two wires came out of the coil. The copper one on the right was out but came off when I was trying to reconnect it. I only have it connected to the silver looking wire on the right. Not sure if I need to reconnect both or if I could even do that without breaking it.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 5:24 pm 
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That coil is the antenna "balun", it changes the antenna connection from two balanced wires at 300 ohms to a lower impedance single wire. If it isn't working then much of the RF signal will be lost.
That length of wire isn't too bad, I was making a general point. When something mechanical breaks like the board, fix it first then see to the wires. The wire are much too fine to support themselves. You also should be prepared for things like this and have some fine wire available, it doesn't have to be insulated much if used in a spot like this.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 6:58 pm 
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One source of fine wire is stranded wire such as lamp cord. Strip a few inches of insulation off and separate out some of the strands. If you have some fine needle nose pliers you can form little hooks at the ends of the wires to make them stay in place while soldering them. And a fine tip soldering iron would help a lot. You do need to connect both wires to that terminal. But do glue that broken terminal board back together before working on the wires.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 7:14 pm 
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I was able to get some picture so if it’s on the lines of working or no signal at all I think I am ok. But I have one more issue before I buy the recap parts. I’m seeing that this set has two 0.033 at 1000v. I would think putting in 0.03 at 1600v would be fine.... Like a 0.47 for 0.5. I just wanna make sure this is the same situation before I buy.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 8:00 pm 
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cameronw wrote:
I was able to get some picture so if it’s on the lines of working or no signal at all I think I am ok. But I have one more issue before I buy the recap parts. I’m seeing that this set has two 0.033 at 1000v. I would think putting in 0.03 at 1600v would be fine.... Like a 0.47 for 0.5. I just wanna make sure this is the same situation before I buy.

It's not a matter of working or no signal. It is more a matter of strong signal or weak and snowy signal.
0.03 at 1600v should work, but I would think that new caps would more likely be available as 0.033 than 0.03. Certainly that is what Sal's Capacitor Corner has. See the advertisement at the right edge of your screen.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 8:53 pm 
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Location: New Hampshire
When working on the antenna input keep in mind this is a hot chassis. The two
red doo-dads are for isolation. They are caps in // with resistors. They pass VHF
but will block low freq AC. You can replace the whole thing with a 75 ohm input
but it must be isolated also. There was a common one you could get off many Japanese brands.

73 Zeno 8)
LFOD !


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Sat 01, 2020 9:32 pm 
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Ill check to make sure the wires are good on the vhf when I start the recap. Just ordered all the caps through sal's.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 4:42 am 
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I ordered all new caps for this set. For one section of the can I will use two 100uf and this 47 to match the original 250. It is kinda hard to show on camera but the 47uf has a slight dent in it. From what I understand this shouldn’t be a problem, but I would like to double check before I start tacking in the new caps.

I really do not have a way to test it. My tools are semi limited. Unless their is a trick with a dmm I am not aware of I don’t think I can check anything.

Thanks and I will try to put the new caps in soon


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 4:16 pm 
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You got that from Sal?
It is probably OK, but the issue may be reliability. If I was picking caps out of a bin I probably wouldn't pick it.
You can use a DVM for a gross test. On the ohms scale, when you first connect it to the meter the reading will be nearly zero, then it will climb in seconds to infinity.
Some digital meters do measure capacitance. You need a vintage cap tester to make sure the cap can withstand the high voltage.

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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 5:18 pm 
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I probably would not use that cap in something I care about. Also 3 caps to replace one should be avoided as a matter of good practice (though it isn't strictly necessary to do so). The closest modern value to 250uF is 220uF and a single 220 should work fine.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 6:41 pm 
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I did get my caps from sal's, but I'm sure this is from shipping. I've always done the ohm test with caps but I figured it never meant anything. Ill probably end up using this cap because I really do not have anything around to order and ordering just one thing is normally a waste. Unless just using the two 100s would work, but I would think that's too low.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 7:07 pm 
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cameronw wrote:
I did get my caps from sal's, but I'm sure this is from shipping. I've always done the ohm test with caps but I figured it never meant anything. Ill probably end up using this cap because I really do not have anything around to order and ordering just one thing is normally a waste. Unless just using the two 100s would work, but I would think that's too low.

200 is only a 20% drop from 250. Most lytics of the tube era were rated -50/+100% so it still should work.

If you do a lot of recap work it can be nice to keep a running stock of often used values and only order once a year in bulk ( I do this and aim for the 10-100 count of each part price breaks on mouser and digikey)...If you have a stock and you have sets waiting to be fixed instead of building an order for each set then waiting for it to come you can just put the set on the bench whenever you want and get going recapping.... It's really nice that way.


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 Post subject: Re: Admiral portable UP9421 help!
PostPosted: Feb Tue 11, 2020 7:20 pm 
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I was wondering why you did not just buy a 270 uf cap but then I noticed that Sal does not have anything that large. If you write to Sal he might send you a replacement even if it might have been shipping damage. But he is closed this week to catch up on the orders he already has.

One way to test that cap would be to connect it to a source of 200 volts through something like a 10 K resistor. Put a voltmeter across the cap and see if it will allow the voltage to go that high without shorting out. To get such a voltage you could put in the 2 100 uf caps with the dented cap connected through the resistor. That way if it does short out nothing would burn up. If it seems OK, remove the resistor.

Even if the cap seems to be OK you may want to replace it the next time you order parts.

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