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 Post subject: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 7:13 am 
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Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
Hi All

I am beginning to take a look at the SX-9 that has been waiting for a spot on the bench. I ran across a component that I have no idea what it is. Can you help identify it?

One end is connected to the grid on the 6F5 1st Audio Amp. The other end is connected to R-20 the Audio Gain pot. Please see the schematic below.

Attachment:
IMG_2475.jpeg
IMG_2475.jpeg [ 141.04 KiB | Viewed 221 times ]


This is what it looks like:

Attachment:
IMG_2474.jpeg
IMG_2474.jpeg [ 174.06 KiB | Viewed 221 times ]


Thanks for the help.

John W.


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 Post subject: Re: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 7:21 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3775
Location: Seattle WA US
That's a C battery, a tiny mercury battery used to bias the first audio stage. Once made primarily by Mallory, they are now unobtainium.
There have been many threads on ARF on work-arounds to replace these cells.

-Chuck K7MCG


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 Post subject: Re: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 7:28 am 
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Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
Thanks Chuck

I should have know you would know the answer. :D I will look for a thread that discusses the work-arounds.

John w.
N7ZMG


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 Post subject: Re: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 7:34 am 
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Joined: Apr Sun 08, 2007 6:47 am
Posts: 4965
Location: British Columbia
K7MCG wrote:
That's a C battery, a tiny mercury battery used to bias the first audio stage. Once made primarily by Mallory, they are now unobtainium.
There have been many threads on ARF on work-arounds to replace these cells.

-Chuck K7MCG


They are carbon zinc cells actually, quite common in many Canadian built radios, this is why some have been able to reactive them by getting water into the dried up electrolyte. Watch batteries are probably the best substitute, but the polarity is the opposite of the bias cells, so the holder has to be rewired.
Regards
Arran


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 Post subject: Re: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 3:59 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10744
Location: Beaver Falls, PA. USA
Remove the bias cell, and replace it with a 0.01 mfd capacitor; then connect a 5 or 10 megohm resistor from the 6F5 grid to ground. The 6F5 will get its operating bias from "contact potential", as was done on millions of AA5 radios.

_________________
Tim KA3JRT


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 Post subject: Re: Hallicrafters SX-9 Unknown component
PostPosted: Sep Mon 20, 2021 8:59 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 816
Location: Suburban Chicago
This is a new one to me! You can read a bit more about them here:

https://antiquewireless.org/wp-content/uploads/09-the_mallory_bias_cell.pdf?force_isolation=true


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