Signal Injection Question
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City: East Brunswick, NJ
My model 46-200 has no sound at all. When I inject a modulated 455 Khz tone at the antenna the 1 khz tone is clearly heard at the speaker. What could be the cause of this disparity? I've replaced most of the caps and the voltages on the tubes seem to be within range of the schematic. The filaments and pilot lamp both are working although I really can't see the 7A8, 7B7 or the 7C6 filaments and don't have a tester for the Loktals. Can someone explain this signal vs. no sound "problem" ?
Welder
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City: Medford OR (OR what?)
Easy. Your IF section works and your RF and or first detector do not. I haven't looked at your schematic.
The long and short of it is to look for a problem prior to the IF with one caveat - the oscillator may also be defective so actually look for your problem prior to the last IF transformer.
"I just might turn into smoke, but I feel fine"
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Posts: 41
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City: East Brunswick, NJ
Thanks Phlogiston. Sounds like a plan. I just replaced the 7C6 converter but no change. I've never replaced an oscillator but could be in my future. Keep you posted.
Thanks!
Happy Holidays !
Posts: 2,118
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OK, I got un-lazy and looked at the schematic. The 7A8 does all of those jobs - as a converter. So look at everything prior to and including the 14A7.
Your 455 signal is being rectified by the 2nd detector just as it would be in normal operation. There is also the remote chance that it could be the 2nd IF trans. The closer the failure is to the detector the less volume you will get with your injected signal. You can use this to trace the failure - if you have the right probes and knowledge- so be careful.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
(This post was last modified: 12-24-2017, 12:04 PM by Phlogiston.)
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I am not sure what to think.
You are injecting the IF signal in the Antenna screw? And it passes?
What exactly does "no sound at all" mean? No reception?
Have you tried the 550kHz to 1600kHz signal injected in the antenna?
Or are you trying to receive stations?
Is your Antenna screw Grounded by chance?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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City: Roslyn Pa
>My model 46-200 has no sound at all.
It would seem that the audio, det, and IF stages are working as you would have no sound when injecting a 455kc signal. Are you experiencing sound but no broadcast stations heard??
Inject a 455kc signal at the ant connection. Turn the generator so you can barely hear it from the spkr. Peak the IF trimmer for maximum signal heard.
One thing to check is the 46-200 has a loop ant that is glued to the inside back edge of the cabinet. Sometimes they are missing. It needs to be there and connected to the tuning cap.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
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City: East Brunswick, NJ
Yikes! Thanks for the responses: My unit uses a 7C6, 2nd. detector and first audio, 7B7, 7A8 instead of the 14's. I also have a scope to use for this signal path. By no sound I mean no reception at all, zilch. I am injecting the signal where the antenna is connected to the oscillator. I have not tried injecting 550 & 1600. The green wire is grounded to the chassis with a screw. The antenna is still in place around the inside the cabinet. One wire goes to the osc. the other to the tuning plate capacitor nearest the back of the chassis. I will try and check the IF cans as you suggested. Thanks so much for all your help. The holidays will put a delay in my future testing but I will keep you guys posted.
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Is your loop antenna ok? Check it for the open. Or unsoldered. Or maybe your chassis is out and it is disconnected.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 41
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City: East Brunswick, NJ
Morzh;
Good point! I can't seem to get continuity but I tried another cabinet and that antenna does have continuity so I tried it but still no reception. Thanks for your post..
Welder
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Looking at the sch on Nos. air going left to right 7A8, then a 7B7 as a sub for the 14A7, third 7C6 as a sub for the 14B6.Fourth tube 50L6. Then a 35Y4 Rect, I would look to see if some one has added a resistor in the filiment string to handle the extra 12 volts. and see if it is correctly installed and not dropping the B plus voltage.
http://www.nostalgiaair.org/pagesbymodel...013591.pdf
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Will try and load info on the 7B7 and 7C6
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So, when you moved between the cabinets, you unsoldered/resoldered the loop antenna, both wires?
AND you grounded the Antenna screw?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 41
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Joined: Jan 2017
City: East Brunswick, NJ
Morzh:
Yes, I did solder (tack) the wires for the other cabinet.
David: Thank you, I'll check out the tubes and possible resistor add. Thanks for the links.
Thanks Guys.
Welder
Posts: 41
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City: East Brunswick, NJ
Morzh:
I forgot to post the antenna screw was grounded also.
You're referring to the green wire I presume.
Welder
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How bout your tuning cap connection?
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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