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 Post subject: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 1:54 am 
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Joined: Oct Fri 18, 2019 1:29 am
Posts: 7
Hello! I’m looking to improve the reception on my radio. I’ve attached an image of the antenna and a print. When the radio chassis was on my bench, the reception wasn’t too bad but now that it’s all back together it’s pretty awful. Any antenna orientation tips? Should I make a connection for a modern AM antenna? Any good internal AM modern alternatives?

Thanks for your time!

-Paul


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File comment: Antenna
65216B35-A5ED-44CE-A712-673EC6B3EB54.jpeg
65216B35-A5ED-44CE-A712-673EC6B3EB54.jpeg [ 194.04 KiB | Viewed 242 times ]
File comment: Radio print
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 Post subject: Re: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 2:38 am 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5903
Location: Near Brandon, Iowa
The antenna and oscillator trimmer cap alignment adjustments must be done with the antenna
held rigidly in the same relative position it will have when both are installed in the cabinet. This is because the steel mass of the chassis will "pull" (detune) the antenna if done otherwise.

If your workbench has a steel top or there are big steel equipment pieces around the place where you did the alignment, that would be an issue as well.

If a re-alignment under the above conditions doesn't improve things, try swapping the connections for the two wires that join the antenna loop to the chassis, and align again.

This is a tuned loop antenna and is very directional.


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 Post subject: Re: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 2:49 am 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5012
Location: Vancouver Island, Canada
Right, for the lurkers, it is an Admiral 6F12, AA6 type circuit with a 35L6.
Besides the tuned loop antenna, it uses that extra tube as an RF amp, amplifying the signal from the antenna.
Turn the radio and you should hear an improvement with the loop broadside to the signal.

If all components are good, it just needs an alignment and some tweaking of the trimmers.
BTW, there is no disgrace in going over the alignment process several times. Some radios don't respond the first time, especially if they've been tampered with before.

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 Post subject: Re: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 3:09 am 
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Joined: Sep Wed 10, 2014 7:13 pm
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Location: Urbana, Illinois
+1 on the advice to position the radio’s loop antenna exactly in the same place it will be when the radio is fully assembled.

Also do not change the length or position of the original factory wires that connect the loop antenna to the radio.

The loop antenna forms a tuned circuit along with the main tuning variable capacitor. Moving it or changing the length of the connecting wires changes the stray capacitance and stray inductance. This throws off the alignment.

I learned this the hard way by thinking I could use clipleads to temporarily lengthen the connecting wires so that I could move the loop antenna out of the way while working on the radio. This simply doesn’t work!

-EB


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 Post subject: Re: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 6:01 am 
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Location: SoCal, 91387
westcoastjohn wrote:
BTW, there is no disgrace in going over the alignment process several times.

AFA peaking the IF transformers, one actually should go over them at least twice. Often times having tweaked the last IF and then doing the first, going back to the last IF after the first was adjusted can produce a still louder generator tone from the set.

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 Post subject: Re: Improving AM reception on 40’s Admiral radio
PostPosted: Nov Tue 19, 2019 12:58 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8918
Location: Long Island
"Awful reception" is a rather broad term that could mean anything. What's "awful?" Noise and interference, which may be inevitable in that particular location depending on what is causing it? Doesn't pick up many stations, which could be an alignment problem or defect in the radio? Hum and distortion? Specific questions garner specific answers.

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