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 Post subject: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Fri 12, 2022 10:24 pm 
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I'm bringing a clean 7070 back to life and am getting close to firing it up - just waiting on the new output transistors and some fuses to arrive - but I've run into a possible issue with the tuner board (F-2614). One of the FM discriminator transformers appears to be missing - T03. The solder pads on the foil side of the board seem to indicate that someone pulled it. Since the alignment procedure references T03 for discriminator adjustment, I'm thinking I'll need to find a replacement. Does anyone have any thoughts about what I could replace it with. I can't find to many specs on that transformer. See photos below for reference. From what I can deduce using the HA1137W datasheet, it's has an internal 100 pF capacitor, but I can't find much else. Photos of F-2614 boards I've found show it has a white adjusting slug . . . I have some 10.7 MHz transformers I could try, but it would be a shot in the dark, I think. Any tuner experts have any thoughts?

Thanks in advance.

Rich

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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Fri 12, 2022 11:07 pm 
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Joined: Jan Tue 31, 2012 12:55 am
Posts: 21367
Location: Bryansford Village. Ireland.
For what it's worth... your TOKO style I.F.Transformer T03
Sansui part number 4235990 or 4235991 (no cross reference found) lol

has a better description (as TO2) in the service manual for model QRX-8001/9001


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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Fri 12, 2022 11:51 pm 
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Thanks Egg. That helps confirm it's a 10.7 MHz coil. I have a few i pulled from old tuners. . . .not much to lose by pluging them in and trying I suppose.

Rich


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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Sat 13, 2022 4:40 am 
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Joined: Aug Wed 14, 2019 5:56 am
Posts: 444
Location: angeles city.philippines,2009
theres a sansui qrx8001 tuner board for sale on ebay that has your part right now for 49$


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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Sun 14, 2022 4:21 pm 
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fonebone wrote:
theres a sansui qrx8001 tuner board for sale on ebay that has your part right now for 49$


Thanks. I'll keep that in mind if I can't get any of my transformers to work.


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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Sun 21, 2022 1:19 am 
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I finished up the 7070 tonight. I installed a 10.7 MHz transformer can that I had pre-tuned (attached photo), finished up all the other work and hooked it up for the alignment. Step 2 in the alignment procedure is the discriminator adjustment and the first part had me adjust my newly installed can to center the tuning meeting. A partial turn brought the meter to center with no issues. The rest of the alignment went well, in spite of the typos and vague instructions that need to be interpolated. AM and FM are now spot-on and work as they should . . . Thanks for all the feedback and suggestions.

Rich

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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Sun 21, 2022 2:14 am 
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Joined: Jan Tue 16, 2007 6:02 am
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Location: Lexington, KY USA
Thanks for reporting back. The concise datasheet seems to say that almost any LC resonant at the IF will work, but that low distortion depends on using just the "right" coil. It provides little help about what might be "right". This coil shifts the phase of the IF signal between two pins on the FM IF & detector IC.

It appears from the photos that the Sansui circuit used two single tuned IF transformers to get a double tuned circuit. So you might have just connected the remaining transformer, T04, to the IC, to make it work to some extent. Almost any 10.7MHz IF can with the correct pinout will probably work for T03 to a degree. If a random replacement works really well, you got a little lucky. But that's fine.

https://datasheetspdf.com/pdf-file/540126/Hitachi/HA1137W/1

Ted


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 Post subject: Re: Sansui 7070 Tuner Board (F-2614) Missing RF Transformer
PostPosted: Aug Mon 22, 2022 3:10 pm 
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Thanks. I missed that blurb in the HA1137W datasheet. My primary goal was to get the tuning meter working, so I needed to add the second coil to the circuit. I'll take luck, lol. I don't typically measure distortion as I don't have the equipment for it, but i can always use more gear. . . I've been doing some reading about using a decent sound card like the Focusrite 2i2 with REW software in lieu of a stand-alone distortion analyzer like the HP 334a~339a series. I'll eventually set that up and give it a try for a future FM alignment.

Rich


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