Hallicrafters SX25 Pitch Control Question

65W200 · **Posted:** Dec Mon 05, 2022 2:45 am

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

Eickerman · **Posted:** Dec Mon 05, 2022 2:14 pm

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

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SX-25 BFO.png [ 198.5 KiB | Viewed 624 times ]

Curtis Eickerman

Wally58 · **Posted:** Dec Mon 05, 2022 2:34 pm

Attachment:

Screen Shot 2022-12-05 at 09.24.40.png [ 183.15 KiB | Viewed 623 times ]

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Screen Shot 2022-12-05 at 09.25.52.png [ 66.02 KiB | Viewed 623 times ]

65W200 · **Posted:** Dec Mon 05, 2022 4:10 pm

Thank you very much, Curtis and Wally.

65W200 · **Posted:** Dec Tue 06, 2022 2:53 am

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

Eickerman · **Posted:** Dec Tue 06, 2022 3:16 am

65W200 wrote:

... with the same number of twists as the
photo in that thread shows?

Yes.

Curtis Eickerman

65W200 · **Posted:** Dec Tue 06, 2022 2:41 pm

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

mrrstrat · **Joined:** May Wed 20, 2020 12:33 am **Posts:** 437

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

65W200 · **Posted:** Dec Sun 18, 2022 7:32 pm

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

Hallicrafters SX25 Pitch Control Question

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