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 Post subject: Field Strength Meter
PostPosted: Dec Sun 22, 2019 1:05 am 
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Joined: Feb Sat 16, 2013 5:08 pm
Posts: 957
Location: Ft. Collins, CO.
I decided to build a similar (but not identical) field strength meter to this one: https://www.airplanesandrockets.com/ele ... 54-man.htm

I have it all together, but can't get the meter to budge. My multimeter is broken and can't measure anything but voltage and shorts.

I have experimentally determined my meter is 0-5 mA. The tube is a subminiature 1J29B, in triode configuration. If I replace the potentiometer with a set of modern Apple earphones, I can hear a signal injected into the grid. No change on the meter. I know every component is working, so... What could the issue be?

All connections are solid. My only modification is to remove the variable capacitor- It shouldn't have anything to do with meter reading.

It seems the issue is the tube isn't outputting enough current, but because I can hear the injected signal, it would seem that current IS flowing. I didn't think these headphones worked under 10 mA, so something is way off.

I'm using 1.5 V across the filaments in series (rated 2 V in series), and 19 V plate voltage.

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-Eli
http://www.FortCollinsB17.org


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 Post subject: Re: Field Strength Meter
PostPosted: Dec Sun 22, 2019 1:43 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Wayside, NJ Monmouth
Reading the text of the build article, the Field Strength meter is made to operate in the 11 or 10 ( 27 - 30 MHz) Meter bands. Are you using it on those bands or on Lower Frequencies ?.


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 Post subject: Re: Field Strength Meter
PostPosted: Dec Sun 22, 2019 2:27 am 
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Joined: Feb Sat 16, 2013 5:08 pm
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Location: Ft. Collins, CO.
I haven't gotten that far yet- I can't get the meter to show any output, even when I add a strong signal to the grid.

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-Eli
http://www.FortCollinsB17.org


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 Post subject: Re: Field Strength Meter
PostPosted: Dec Sun 22, 2019 6:36 am 
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Location: Tucson, Arizona U.S.A.
Do you have a data sheet for that tube? Perhaps it isn't capable of driving a 5 mA meter, especially with such a low B+.

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Jim Mueller


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 Post subject: Re: Field Strength Meter
PostPosted: Dec Sun 22, 2019 6:52 am 
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Joined: Feb Sat 16, 2013 5:08 pm
Posts: 957
Location: Ft. Collins, CO.
Jim Mueller wrote:
Do you have a data sheet for that tube? Perhaps it isn't capable of driving a 5 mA meter, especially with such a low B+.


Thank you for saying that! You solved my problem. I feel a bit silly now, but I didn't have a high enough B voltage to drive the meter.

45 is too much, 18 too little, the sweet spot is somewhere in the middle, thus having the potentiometer to adjust. They use 30 V, which I bet is just about where I need to be as well.

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http://www.FortCollinsB17.org


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 Post subject: Re: Field Strength Meter
PostPosted: Dec Mon 23, 2019 6:01 pm 
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viewtopic.php?f=12&t=369454

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