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 Post subject: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Mon 05, 2022 2:45 am 
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Joined: Dec Sun 04, 2022 3:04 pm
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Location: Lockport NY
I'm trying to determine the connection for one of the terminals on the BFO/ Pitch Control
dial. My SX25 came to me in pretty rough shape with various cut/broken wires. The
schematic has this going into the plate of the "V9" 6SQ7 from the BFO switch [SW3]
if I'm reading the schematic correctly? If anyone can confirm this, I'd appreciate it.

John


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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Mon 05, 2022 2:14 pm 
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65W200 wrote:
I'm trying to determine the connection for one of the terminals on the BFO/ Pitch Control dial. My SX25 came to me in pretty rough shape with various cut/broken wires. The schematic has this going into the plate of the "V9" 6SQ7 from the BFO switch [SW3] if I'm reading the schematic correctly? If anyone can confirm this, I'd appreciate it.John
To clarify, it goes from the Grid of the 6J5 pin 5 to the Detector Plates of the 6SQ7 which are tied together (pins 4 and 5). It goes there via capacitor C20 (I think, it's pretty blurry). It does not go to the audio Plate (pin 6).

The switch goes to B+ which could be about anywhere (it just supplies power to the BFO).

http://www.nostalgiaair.org/PagesByMode ... 008915.pdf
Attachment:
SX-25 BFO.png
SX-25 BFO.png [ 198.5 KiB | Viewed 624 times ]
Curtis Eickerman

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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Mon 05, 2022 2:34 pm 
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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Mon 05, 2022 4:10 pm 
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Joined: Dec Sun 04, 2022 3:04 pm
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Location: Lockport NY
Thank you very much, Curtis and Wally.


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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Tue 06, 2022 2:53 am 
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Joined: Dec Sun 04, 2022 3:04 pm
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Location: Lockport NY
Alright....I looked up the capacitor [C30] and it is a "Twisted Pair" type.
I found this other SX25thread that talks about it......
viewtopic.php?f=5&t=335490
I figured I can solder a piece of wire on Pin #4 on the 6SQ7
and twist it together with the wire that was hanging off of the
Pitch Control terminal with the same number of twists as the
photo in that thread shows?

John


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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Tue 06, 2022 3:16 am 
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65W200 wrote:
... with the same number of twists as the
photo in that thread shows?
Yes.

Curtis Eickerman

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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Tue 06, 2022 2:41 pm 
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Eickerman wrote:
65W200 wrote:
... with the same number of twists as the
photo in that thread shows?
Yes.

Curtis Eickerman


Alright Curtis. I'll do just that. Thanks again.

John


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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Mon 12, 2022 2:55 am 
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That might work - I would copy what I saw on another set and tune its performance but messing with the BFO knob and seeing what works best. I did that with a SX-20, 20R, my SX-25.

65W200 wrote:
Alright....I looked up the capacitor [C30] and it is a "Twisted Pair" type.
I found this other SX25thread that talks about it......
viewtopic.php?f=5&t=335490
I figured I can solder a piece of wire on Pin #4 on the 6SQ7
and twist it together with the wire that was hanging off of the
Pitch Control terminal with the same number of twists as the
photo in that thread shows?

John


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 Post subject: Re: Hallicrafters SX25 Pitch Control Question
PostPosted: Dec Sun 18, 2022 7:32 pm 
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Joined: Dec Sun 04, 2022 3:04 pm
Posts: 10
Location: Lockport NY
mrrstrat wrote:
That might work - I would copy what I saw on another set and tune its performance but messing with the BFO knob and seeing what works best. I did that with a SX-20, 20R, my SX-25.


There was another SX25 thread that had phots and an explanation. It matched the schematic I had as well. I put the second wire in place, trimmed it
to length and twisted it together with the other and the BFO/Pitch seem to function fine.

John


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