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  #31  
Old 09-19-2016, 11:17 AM
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bandersen bandersen is offline
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Sure, I understand. What I typically do is pull the 5U4 rectifier tube for the first power up. That will kill B+ to the entire set and only the filaments get power. Then I put my DMM in AC mode and probe the 5U4 socket. Should have around 5 VAC for the filament and 700-800 between the plates. That's a quick way to see if the power transformer is any good without risking damaging anything.
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  #32  
Old 09-19-2016, 11:51 AM
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Quote:
Originally Posted by Crist Rigott View Post
You're right. Seeing the rectifier tube was pulled. Just being overly cautious and still being new to this.
If you are worried about protecting the flyback while testing other stuff the better tube to pull would be the Horizontal output.
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  #33  
Old 09-19-2016, 11:57 AM
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Quote:
Originally Posted by Electronic M View Post
If you are worried about protecting the flyback while testing other stuff the better tube to pull would be the Horizontal output.
Pulling the rectifier tube is the first thing I do!
On the horiz out, remove the entire tube, not just the plate cap. Just lifting the plate cap, can still destroy the H.O, because of no plate voltage.
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  #34  
Old 09-19-2016, 12:37 PM
Crist Rigott Crist Rigott is offline
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All good stuff. Thanks guys for the tips. I'm going to check for the high voltage from the transformer at the 5U4G tube. I didn't do that yet.
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  #35  
Old 09-19-2016, 12:43 PM
Crist Rigott Crist Rigott is offline
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612vac at the 5U4G tube pins 4 and 6. Riders says 310vac each side.
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  #36  
Old 09-21-2016, 12:45 PM
Crist Rigott Crist Rigott is offline
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Guys, I could use a little help. I am checking the mica caps as to their location in the chassis and their values to compare them to the schematic. I think one of them isn't the value as shown on the schematic, both Sams and Rider's. I've taken close ups of the micas and would like some help in reading the dot codes. I've got the Radio Daze color page describing how to read them.

What I would like is for you guys to confirm their values from the pictures. Just to see if I'm reading them right.

The 1st one is C403. Yellow, violet, black, brown, silver, orange
The 2nd one is C404. White?, yellow, violet, red, silver, black
The 3rd one is C413. Grey, red, black, white?, silver, green
The 4th one is C420. Yellow, violet, black, black, silver, blank
The 5th one is C421. Yellow, blank?, black, red, silver, black

Thank you for your help.










Last edited by Crist Rigott; 12-03-2016 at 08:57 PM.
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  #37  
Old 09-21-2016, 01:08 PM
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Here are my best guesses

1st 47 pF (might be 4700 ?)
2nd 470 pF
3rd 82 pF
4th 47 pF
5th 1000 pF
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  #38  
Old 09-21-2016, 01:20 PM
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Remember most schematics don't reflect some or all production changes (Admiral had MANY), schematics (especially Sam's) had errors/typos, and that if it was factory wired the way it currently is then it is likely to work better being left alone than it will if you make it match the schematic. So it is most advisable to leave the factory wiring config alone till you finish recap and other avenues of troubleshooting.

Also you probably know this, but micas rarely fail and often are in circuits that require re-alignments after cap change (sometimes even lead dress changes can upset it). Leave micas under 1000pF alone unless you have good reason to believe they are bad. Ones over 1000pF often are not really micas, but paper caps in mica's clothing, and as a matter of policy I normally change them.
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  #39  
Old 09-21-2016, 09:00 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by bandersen View Post
Here are my best guesses

1st 47 pF (might be 4700 ?)
2nd 470 pF
3rd 82 pF
4th 47 pF
5th 1000 pF
Bob, Thanks for taking the time to reply. It's appreciated.

#1 is listed as C403 .0047mfd mica or 4700pf
#2 is listed as C404 .006mfd mica or 6000pf
#3 is listed as C413 82mmfd mica or 82pf
#4 is listed as C420 470mmfd 5% mica or 470pf
#5 is listed as C421 .001mfd 5% mica or 1000pf

Both Sams and Rider's agree on the values. As you can see #1 and #2 differ. #3-5 agree with both parts lists. BTW the part designators are from Rider's.

I then remembered that my multimeter can check the values of capacitors. Both #1 and #2 measured out to 4.70nf or 4700pf.

I really don't know why the color code is so difficult to determine the value of these caps.

Looks like I'll be using 4700pf 5% 500V Silver Micas for their replacement.

I'm including the schematic from Rider's.
Attached Files
File Type: pdf 20T1 Schematic.pdf (688.1 KB, 5 views)
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  #40  
Old 09-21-2016, 09:24 PM
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OK. I can see the 2nd one has a red multiplier dot I thought was brown earlier. As for the first. I think it's a variant that has three digits (yellow. violet, black) then a X10 multiplier (brown).

As Tom mentioned, Admiral did many production run changes. You should have a run # stamped somewhere on your chassis.
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  #41  
Old 09-21-2016, 10:13 PM
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I dug up a whole page of 20T1 production changes in the Wallace Teleaide for Admiral. Click for a larger version.



No mention of C404 but this may explain it. There were parts shortages due to the Korean conflict and high consumer demand so substitutions were made.
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  #42  
Old 09-21-2016, 10:26 PM
Crist Rigott Crist Rigott is offline
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Wow, Thank you Bob. Is there anyway that I can save those prints? I tried to save them as an image and the resolution was bad. But I can view them very clearly.

Thanks again.
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  #43  
Old 09-21-2016, 10:43 PM
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Clicking on them should take you to Flickr where you'll have options to save it in a variety of resolutions. Here's a link to the full size version.

https://c5.staticflickr.com/9/8032/2...b897ea12_o.jpg
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  #44  
Old 09-22-2016, 01:20 AM
Crist Rigott Crist Rigott is offline
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Got it!

Thanks Bob.
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  #45  
Old 09-25-2016, 09:45 PM
Crist Rigott Crist Rigott is offline
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As I do with the radios and TV's I restore, I label all the components using the SAMS designators. This allows me to see what is in the TV, part-by part. Also I check the component against Sams schematics. When done, I compile my resistor and capacitor parts lists.

Next up is to order what I need.


Last edited by Crist Rigott; 12-03-2016 at 03:38 PM.
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