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 Post subject: Atwater Kent Choke Coil ?
PostPosted: Jan Wed 13, 2021 4:01 am 
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Location: West Dennis, Ma. 02670 (Cape Cod)
Just curious, The Atwater Kent Radio's (35's) had a coil that attached to the antenna on one end, with the other end to gnd. This same connection that had the antenna connected also went though a resister to the grid of the first stage.

Why did Atwater Kent call this coil a "choke coil" ?

Marc


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Wed 13, 2021 5:18 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Marc

It is a two wire non tuned choke for RF frequencies. Like a filter choke in a radio but for use with RF.

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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Wed 13, 2021 6:55 pm 
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Location: Austin, Texas
The reason for the choke is to ground the antenna at low frequencies. That prevents build up of a static charge that would cause noise and possibly damage. It looks like an open circuit at radio frequencies so the signal from the antenna goes to the first tube with only a small loss.

Jay


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 1:28 am 
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Thanks for the information. I also note that the input is direct to the grid without a matching transformer or tuned circuit.

Seems that a specific type of antenna is needed.

Marc


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 2:11 am 
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A tuned loop would be a good choice. With the first stage trying to amplify all frequencies, you can get a weird mix of signals on the plate.

Jay


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 2:12 am 
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Marc Hildebrant wrote:
Thanks for the information. I also note that the input is direct to the grid without a matching transformer or tuned circuit.

Seems that a specific type of antenna is needed.

Marc
Ya, a long wire :wink:

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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 2:18 am 
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Joined: Mar Wed 16, 2011 10:44 pm
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Location: Peekskill, NY
Some atwater kents have that input choke tapped , the grid is tapped down on the coil. In my model 53 the volume control is a variable resistor,
so the antenna and the grid do have a dc return even if that choke coil were not there. I would think that just replacing the coil with a few K resistor
would have been cheaper, so AK probably had some intricate reasoning for using it.


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 3:51 pm 
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Joined: Jan Sun 13, 2013 10:38 pm
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Location: West Dennis, Ma. 02670 (Cape Cod)
Looking through my schematics, I noticed that the model 20C and others used a tuned circuit on the grid side of the first RF stage while the 35 used the RF choke in the grid side. This must be related to a single tuning knob verses individual tuning for each RF stage.

The Atwater Kent design team for the single tuning knob must have needed to have the tuned circuit on the other side of the RF Stage to make the stages track each other. Having the tuned stage after the gain stage makes it less sensitive to the antenna (at least its a good story).

Marc


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 Post subject: Re: Atwater Kent Choke Coil ?
PostPosted: Jan Thu 14, 2021 4:20 pm 
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Joined: Mar Wed 16, 2011 10:44 pm
Posts: 1658
Location: Peekskill, NY
It's a good theory. Later coupled tuning sets like the 33 had a tuned circuit at the first stage but it had a trimmer capacitor to account for
differences in the antenna.


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