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Antique Radio Technical Forum
Grunow 660 - Help!!

Posted by JF on 04/15/2009 16:21

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HI Steve, May not help but when I fired up my 670 it was very faint as well until I put the shields on the tubes, probably not it but make sure they are on...Jeff
Grunow 660 - Help!!
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:This is the first real radio that I've had to fix so this is all a big learning curve for me. I appreciate everyone's patience in helping me out with this.
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:To get you up to speed, I've done a recap on the radio (everything but the micas) and I had to rebuild the circuitry under the 2nd detector (under the 75 tube) to get it back to original spec. I then tried it out and was able to get stations when I had the ground hooked up to a water pipe. The stations were faint but the local stations came through the best. The volume control didn't do any amplification at all when I turned it.
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:So I took another look at the radio and found that the secondary on the 2nd IF tranformer had a resistance of 598k (the resistances of the other IF coils were all between 20 and 40 ohms). So I thought to myself this has got to be it so I used Norman Leal's article to bypass the secondary by connecting a 250pF cap from pin 2 on the 6D6 IF to pin 3 on the 75, connecting a 100k from pin 3 on the 75 to the 100pF cap and disconnecting the secondary wire from the 75. I tried the radio again and I got the same response as before - faint channels, no volume control.
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:So then I checked all the resistances and found that both of the 500k's had drifted to about 750k each, the 2 250k's had drifted to about 450k each. But the big one was the 100k off of pin 2 on the 75 - it was open. Again, I replaced all these resistors thinking that this was it... But when I tried it, now I don't get any stations coming through at all but the speaker does sound like it's getting power now (and now I have volume control) because I have a loud hum. I'm not sure what to think now. My gut is telling me it might be either the 42 power tube or that the IF bypass isn't working the way I think it should work???? I checked the 42 on my Heathkit emission tester and it tested at about 59% out of 100 - no shorts.
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:Sorry for the long winded post - I'm at wits end ;-)
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Grunow 660 - Help!! 
Steve Bento 04/15/2009 14:53 
JF 04/15/2009 16:21 
Doug Criner 04/15/2009 16:43 
Steve Bento 04/15/2009 17:16 

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