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Author Topic: Johnson Navigator filter choke?  (Read 909 times)
W1BR
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Posts: 4195




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« on: December 02, 2018, 07:58:28 PM »

Manual says it is 10 Henry, but I suspect it is a swinging choke... does anyone have a good idea of its inductance specifications? (choke input power supply.)

I noticed mine was has indications that it was once severely overloaded at one time, probably related to the two 20 amp fuses some fool installed in the Eldico AC plug before I got the transmitter. Choke is discolored and smells like it was burnt.  Still works, but I want to be prepared in case it shorts or opens.

Pete
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N2EY
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Posts: 5093




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« Reply #1 on: December 03, 2018, 08:48:23 AM »

Here's a semi-educated guess:

1) The 6146 plate voltage varies from 340 volts key-down to 405 volts key up.

2) The dropping resistor for the VR tube is a 22K unit. 405 volts minus 150 volts gives 255 volts and 11 mA through the VR tube, key up. Assume a few mA for the keyer tube, giving total key-up load of 15 mA.

3)  Key down, the 6146 draws 115 mA plate current. Assume about 45 mA for all the other stages - that's a total of 160 mA full load.

405 volts divided by 15 mA gives 27,000 ohms total load key up. 340 volts divided by 160 mA gives 2125 ohms total load key down.

For a choke input filter with 60 Hz full-wave single phase rectifier, the choke inductance needs to be at least the load resistance in kilohms. So a swinging choke that has an inductance of 27 H at 15 mA and 2.125 H at 160 mA would be just adequate.

73 de Jim, N2EY

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W1BR
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« Reply #2 on: December 03, 2018, 11:53:07 AM »

Thanks Jim.  I will file that info.

I have the TX running, and nothing seems to be failing. Hopefully the filter choke will last for a few more decades. I guess that overheated choke is an indication why a previous owner decided he needed 20 amp fuses... LOL. 

Pete
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N2EY
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« Reply #3 on: December 03, 2018, 02:20:00 PM »

Thanks Jim.  I will file that info.

I have the TX running, and nothing seems to be failing. Hopefully the filter choke will last for a few more decades. I guess that overheated choke is an indication why a previous owner decided he needed 20 amp fuses... LOL. 

Pete

A failing choke can be a reason for chirp because the key up and key down voltages are much farther apart.

73 de Jim, N2EY
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W1BR
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« Reply #4 on: December 03, 2018, 02:51:49 PM »

Voltages are well within  spec according to the manual.  Chirp problem is fixed, at least for now.  I have a resistance value for the choke so if turns do short I will have some clue as to what is changing.

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W9ALD
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Posts: 44




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« Reply #5 on: December 03, 2018, 09:16:14 PM »

You could place the choke in a container with varnish in it.  Then pull a vacuum on the container for a couple of days.  Then remove the choke and let it sit in the sun for a few days.  Once the varnish has dried do it again a time or two.
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KM1H
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« Reply #6 on: December 07, 2018, 05:29:25 PM »

Not a good time in CT for sun baking. That is small enough for the family oven Grin Roll Eyes
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W9ALD
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« Reply #7 on: December 07, 2018, 07:22:50 PM »

We had 8 inches of white and fluffy last week here in Waseca ... an oven would be wonderful.
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The mere presence of a signal is more important than it's magnitude.
KM1H
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« Reply #8 on: December 08, 2018, 09:24:53 AM »

Bare ground and a sunny 13F here this morning, the 8" melted weeks ago.
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W1BR
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« Reply #9 on: December 24, 2018, 12:32:26 PM »

Found a 8.5H 200mA open frame choke that matches the mounting holes, although considerably heavier and beefier than the original it fits in the available space with no mods. Works fine, key up to key down is from 414 volts to 371 volts...  as good, if not better than the old choke.
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