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  #16  
Old 05-13-2016, 09:24 PM
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The link works for me. Might want to try right clicking and choosing 'Save Link as'. Takes forever for my browser to open the PDF if I simply open the link.
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  #17  
Old 05-13-2016, 09:33 PM
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Link akso works fine for me... but here is another resource from AK:

http://akdatabase.org/AKview/display...album=35&pos=0

jr
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  #18  
Old 05-13-2016, 10:07 PM
Captainclock Captainclock is offline
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Quote:
Originally Posted by WISCOJIM View Post
It's a 27-page PDF file. Must be some trouble on your end.

.
Yeah it will let me navigate through the pages but the printed pages themselves aren't showing up in the PDF Download. So I'm not sure what's going on.
So I figured out that it must of been my Adobe Reader plugin on my web browser that was screwing things up because when I downloaded the file onto my computer and then opened it with Adobe Reader on my Computer it worked fine.

Last edited by Captainclock; 05-13-2016 at 10:15 PM.
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  #19  
Old 05-14-2016, 09:19 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Captainclock View Post
I believe mine's an original 21 so I don't think it has any IC chips in it. The electrolytics don't appear to be bad but of course they could be bad even if they don't look it (no cap bulge). The electrolytics are mainly on the amplifier board, there aren't any on the tuner board surprisingly enough. Now I noticed that the Model 21 has an RCA Plug that says "Tuner out" was this meant to be able to have a multiplex unit hooked up to it so it could be FM Stereo like the Model 8? Also I'm missing one of the knobs on this unit and I was wondering where I might source a replacement knob for this unit.
The ua703, if made by Fairchild, looks like a slightly larger transistor. The brown button ones were extremely unreliable. IIRC, they were replaced by a GE-IC12, NLA.
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  #20  
Old 05-14-2016, 10:59 AM
Captainclock Captainclock is offline
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Originally Posted by dieseljeep View Post
The ua703, if made by Fairchild, looks like a slightly larger transistor. The brown button ones were extremely unreliable. IIRC, they were replaced by a GE-IC12, NLA.
So What's the modern substitute for this part? Is there an NTE Part that subs out for this part?
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  #21  
Old 05-14-2016, 12:02 PM
WISCOJIM WISCOJIM is offline
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Some members here may still have some epoxy ones in their parts bins, but you may have to substitute one of these metal ones:

http://www.amazon.com/IC-AMP-8-LEAD-...productDetails



.
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  #22  
Old 05-14-2016, 12:08 PM
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Am I missing something here? I don't see any ics in the schematic for the set... just 11 transistors

jr
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  #23  
Old 05-14-2016, 12:22 PM
WISCOJIM WISCOJIM is offline
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There are multiple version and revisions of the Twenty-One.

From the looks of his, it's probably one of the early (non-IC) versions.

Pictures of the boards inside his unit could confirm this.

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  #24  
Old 05-14-2016, 12:32 PM
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Interesting! thanks for the info... guess we need some chassis pix.

jr
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  #25  
Old 05-14-2016, 12:34 PM
Captainclock Captainclock is offline
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Here's some pictures of the insides of the unit.

First picture is of the tuner board, second picture is of the IF board, third picture is of the amplifier board.
Attached Images
File Type: jpg DSCN2815.jpg (81.2 KB, 25 views)
File Type: jpg DSCN2816.jpg (79.4 KB, 29 views)
File Type: jpg DSCN2817.jpg (100.5 KB, 30 views)
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  #26  
Old 05-14-2016, 02:02 PM
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Since the IF board is shielded, I can't see if the active devices are transistors or ics.

But first things first, regardless of the type of device used for IF amplification, IMHO, the hum problem needs to be resolved before further problems can be addressed.

jr
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  #27  
Old 05-14-2016, 03:02 PM
Captainclock Captainclock is offline
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Quote:
Originally Posted by jr_tech View Post
Since the IF board is shielded, I can't see if the active devices are transistors or ics.

But first things first, regardless of the type of device used for IF amplification, IMHO, the hum problem needs to be resolved before further problems can be addressed.

jr
Well if the filter capacitor wasn't the cause of the hum (it still hummed even after the filter capacitor was replaced) what else could cause the radio to have a 60 Hz hum?
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  #28  
Old 05-14-2016, 03:11 PM
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Post 9 jr tech mentioned the rectifiers. My thought too. You checked both of those?
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  #29  
Old 05-14-2016, 03:14 PM
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My first guess was on post 9 (bad power supply diodes), but there are additional filter caps on the audio board to check/ replace. Shorted output transistors could also place a hogh load on the power supply and cause hum.
Does the volume control change the loudness of the hum or is it always there?

jr
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  #30  
Old 05-14-2016, 03:50 PM
WISCOJIM WISCOJIM is offline
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Is the hum still there when the volume is all the way down?

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