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Antique Radio Technical Forum
46-1209 No SW

Posted by Dave Froehlich on 06/27/2007 15:56

OK, I will add the resistor. The 7AF7 may be identical to the 7F8 except for Pin-out. So it might work. I'll let you know what happened when the 10K ohm resistor is added.


:Hello All,
:: In this radio's past someone replaced the 7F8 with a 7AF7 and did a little re-wiring to make it work. I remember mentioning this here, but I don't remember when. Anyway, AM Broadcast band is working. When I got it, there was a 500 ohm resistor connecting the both cathodes together. This was incorrect. I added the correct 2.2K ohm resistor to the mixer cathode, and disconnected the 500 ohm resistor. So the BC is fine.
:: The resistor on the SW front end is missing. But I don't see how it would make any difference. It's in parallel with a coil and trimmer capacitor. I get continuity on the SW oscillator coil. Maybe this tube wont work at SW frequencies? It seems that it should. So I'm not going to re-wire for the 7F8. SW does pick up clicks and things but no actual broadcasts.
:: I haven't tried to put another radio radio near the oscillator coil to see if it's oscillating on the SW band. But I think that it's a good next step, not finding anything else wrong.
:: What should I look at next?
:If it were mine, I would put it back the way it was designed, then go from there. A resistor across a coil is for dampening; if it was made that way it was necessary for proper operation.

46-1209 No SW 
Dave Froehlich 06/27/2007 14:26 
Johnnysan 06/27/2007 15:40 
Dave Froehlich 06/27/2007 15:56 
Dave Froehlich 06/27/2007 16:05 
Radiodoc 06/27/2007 16:15 
Edd 06/27/2007 17:36 
Dave Froehlich 06/27/2007 18:02 
Dave Froehlich 06/27/2007 18:18 
Edd 06/27/2007 18:27 
Dave Froehlich 06/27/2007 19:31 
Dave Froehlich 06/27/2007 20:12 
Elton 06/27/2007 21:33 
Radiodoc 06/27/2007 21:43 
Edd 06/28/2007 10:06 
Dave Froehlich 06/28/2007 21:14 
Fred R 06/29/2007 14:06 
Dave Froehlich 06/29/2007 14:54 
Dave Froehlich 06/29/2007 15:17 
Dave Froehlich 06/29/2007 15:19 
Dave Froehlich 06/29/2007 15:24 
Fred R 06/29/2007 17:07 
Fred R 06/29/2007 18:36 
Dave Froehlich 06/30/2007 06:20 
Fred R 06/30/2007 07:41 
Dave Froehlich 06/30/2007 20:20 
Thomas Dermody 06/29/2007 15:27 
Paul Knaack 03/27/2010 15:30 
Mike C. 03/27/2010 18:27 
Mike C. 03/28/2010 17:27 
Dave Froehlich 04/02/2010 23:16 
Ian 04/07/2010 02:03 
Ian 04/07/2010 02:03 

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