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 Post subject: Admiral 5X12-N
PostPosted: Mar Mon 05, 2018 4:57 am 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
Started on the new restoration project. All capacitors have been rebuilt. Any resistors that were not within specification were replaced. Radio powers up. I get a strong static sound through the speaker. Try to proceed with the alignment process. Could not find a tone from the signal generator anywhere on the radio dial. Went through the voltages and resistances Of all the pins on the five tubes. Everything looked pretty good, except I get no resistance reading on pin eight of 35Z5. Any recommendations on a next step.

Thank you

Jeff


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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Mon 05, 2018 5:55 am 
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First off, if radio isn't at least receiving some stations, alignment is almost always 100% useless... It's far from the cure all that's often presented here...

On pin 8 you should get a low resistance increasing to maybe infinity as caps charge... No reading at all suggests caps are bad or incorrectly installed... Try reversing polarity to see if there is a reading... If you already have, find out what's open...

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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Mon 05, 2018 10:42 pm 
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Joined: Dec Sat 23, 2006 5:49 pm
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Location: missouri ozarks
I like the Admiral radios of this period, but they are often infected with SMD. I own one with the condition. Check to see if there is positive voltage on the grid of tubes following the IF transformers. If there is, you have a case of SMD. IF not, you are lucky. Use your signal generator and find out where the signal is being lost. If the static in the speaker sounds like lightning crashing, with no signal getting through, you should at least suspect SMD. Good luck.

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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Fri 09, 2018 11:23 pm 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
Here are the measurements. Also, there is a component which I have not previously encountered, called a couplet. I changed it out, and replaced with individual components.

Jeff


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2018-03-09 16.16.21_resized_1 (2).jpg
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Last edited by SakanaLuvr on Mar Sat 10, 2018 1:25 am, edited 1 time in total.
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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Fri 09, 2018 11:25 pm 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
And the ohms............


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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Sat 10, 2018 9:08 pm 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
I continue to have only loud static. 2 measurements are consistently out of spec. The voltage on plate 1 of 12SQ7, and the resistance on the cathode of 35Z5. I have even swapped out valves for ones which are from working radios. Suggestions for a next step are gladly welcomed.

Jeff


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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Sat 10, 2018 9:12 pm 
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Location: SoCal, 91387
My first test on a set receiving no stations is to do the second radio test, to ensure that the osc is functioning. Sounds like your's isn't.

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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Sat 10, 2018 11:06 pm 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
I can hear a harmonic tone on the good radio set on 970, with the admiral on 630. Not 455 apart, but there does appear to be a harmonic signal. A repeat attempt was made to do the alignment, and I started to hear some signal tone. Unfortunately, the ferrite core in 72B51, the 2nd IF coil, has stripped, and is just spinning in the hole. Unless someone has a fix for this, I will be looking for a replacement 2nd IF transformer.


Last edited by SakanaLuvr on Mar Sun 11, 2018 4:08 am, edited 1 time in total.

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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Sun 11, 2018 3:34 am 
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With proper B+, the resistance on 35Z5 cathode is irrelevant...

Voltage on 12SQ7 detectors is likely upset by the noise, possibly caused by SMD... Can also upset it's plate voltage in audio...

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 Post subject: Re: Admiral 5X12-N
PostPosted: Mar Sun 11, 2018 4:07 am 
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Joined: Jul Sat 23, 2016 6:58 am
Posts: 371
Location: La Quinta, CA
I was able to get the radio aligned. The ferrite core in the IF coil was free spinning. The threads have stripped. I was able to slide the core enough to bring it into alignment. Actually picking up quite a few stations. Wondering if I should put a drop of glue on the core to keep it stationary? Any recommended technique for this? Also thought about simply replacing the whole coil. There are many 455 KC and 456 KC IF transformers on oldradioparts.com. Can anyone suggest a suitable 1 1/8” transformer from that site?

Thank you
Jeff


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