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Started work on Admiral 7T10. Recapped and all new resistors. Tubes all checked good. Only get one station across the dial. Narrowed down to oscillator- I think. Voltage readings on 12SA7 tube as follows:
Pin 1--0
Pin 2--13 vac
pin 3--83 vdc
pin 4--83vdc
pin 5--0--should be -7
pin 6--0
pin 7--26vac
pin 8-- -5.2--should be -.8 The only caps not replaced were C2 and C11- both are ceramic 50pf and 20pf.
How to check for bad oscillator? Could C2 and C11 be open/shorted.
http://www.nostalgiaair.org/PagesByModel...000212.pdf
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Certainly looks like the oscillator is not running. I would check the oscillator coil for continuity before looking at those two caps. Not likely (but possible) that they are your problem.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Agree with Jerry. You can test the osc coil in circuit all three pins should have have continuity to each other , a low resistance in the order of 10 ohms or less. If not that's your problem. Universal replacement are available from AES.
GL
Terry
Got a 7T04 in the basement myself.
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Thanks guys. I get a few ohms on one set and nothing between the other.
I looked on AES site and there are three replacements available. Which one? Should I replace C2 and C11 while I'm there? I can order them all together.
Thanks,
Joe
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Your call Joe on the caps. Seriously doubt they are bad but the shipping costs as much as the parts, might as well throw them in the order. JMHO I will let someone who knows more than me to suggest the replacement coil. That would include most on the Phorum.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
(This post was last modified: 01-29-2013, 07:23 PM by
jerryhawthorne.)
Posts: 7,301
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Posts: 1,562
Threads: 56
Joined: Nov 2008
City: Sedona, AZ/Placentia/CA
A friend in need is a pest! Bill Slee ca 1970.
Posts: 1,562
Threads: 56
Joined: Nov 2008
City: Sedona, AZ/Placentia/CA
Joe, looking at the schematic it appears the cheap 3 lead coil should do just fine.
Jerry
A friend in need is a pest! Bill Slee ca 1970.
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Thanks Jerry. Will order shortly and will let you know. Thanks to all.
Joe
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Hi Joe,
You can try 3 wire osc coil and see if it works (probably will) but nice thing about the $9 one is that it has a slug in it so you can adj the frequency at the low end of the band. With other one you can only set the high end with the trimmer and the bottom falls wherever.
GL
Terry
Actually years ago I had one of those Admiral set great player!
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