Comments for page: SB-620 Mods

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Posted by Steve L. March 02, 2022 - 07:56 am
Hi Bill W, Thank you for your kind comment. Sorry that you're having trouble finding a pip. I take it that you've done the relevant steps in the "Adjusting the Scanalyzer" section on page 9 of the article? On page-10 have you gone through the steps in the four paragraphs of the second bullet point starting with "During operation..."? Since further troubleshooting may get into minute detail, it would be best if you email me directly. You can find my address on the About page by clicking the About... button near the top of the Home page. I will be happy to help.

Posted by Bill W March 01, 2022 - 05:18 pm
Hi Steve: Great article on the Heath sb-620. I have one that had an odd combination of coils installed. The oscillator coil was # 40-807, the pass band coil was #52-101 and the L1 coil was a 40-590. After recapping the entire unit, I was able to find the pip at about 5mhz. The problem is I need an IF of 3.395 for my SB-300. I decided to build your oscillator coil leaving the pass band coil alone. I built the L3 coil per your specs and followed the Heath installation instructions .Now I can't find a pip at any frequency. No amount of adjusting L3 locates it. The unit worked fine with the 40-807 for 5mhz. I guess no one has tried mixing your L3 with the Heath L2. Any Ideas.

Posted by Steve L. February 05, 2021 - 04:17 pm
Hi Steve W., Using an SB-620 which has been set up for 455kHz with the Collins 500kHz IF is an interesting question. First, bear in mind that this article is about converting a 455kHz SB-620 to 3395kHz, and I haven't used the SB-620 at the lower frequency. However, I studied the schematic and manual to investigate your question. The short answer is that I think it will be okay for that. Encouraging signs are (1) the target IF is only 10% away, (2) the 455kHz prefilter shown in the schematic seems broadly tuned, (3) the C16/L2 tank in the 455kHz prefilter is the same one shown for the "all other frequencies" option, including 1.0MHz.

When SB-620 is set up for 455kHz, sweep width is specified as 10 to 100kHz. That's good in that you only want to move 45kHz, which is within sweep range. The only concern is that, if centering range isn't copious, you might find tuning a bit cramped. Adjusting variable cap C4 should fix that. Worst case, C4 could be reduced in value. Good luck with your project and please let us know how it goes. Will be happy to help if you have further questions.

Posted by Steve W February 04, 2021 - 05:18 pm
I have a collins r388 that has a 500KC i.f and has an i.f output , has anyone ever tried connecting and tuning it for 500KC and did it work correctly ?
thank you for any advice


Posted by Steve L. February 24, 2020 - 03:06 pm
The reply to Kelley's message of February 19, 2020 - 07:02 pm can be seen here: Heathkit_SB-620.pdf
Please note that the posting dates/times for that thread are incorrect because it was an email exchange and was later posted in Reader Comments. The email exchange continued and the rest is available on request.

Posted by Kelley - WRK February 19, 2020 - 07:02 pm
Hi Steve, Attached are three images of my IC-746. Main is of the main board area, Bottom is the entire bottom of the radio, and Rear is the rear of the radio. The radio is laying on its top.

IC631 is to the left of the three filter canisters in the Main image. It has what I'm assuming are either four silver capacitors or transistors around it.

I have some RG174 coax which is very small 50 ohm coax. I'm not sure how to get the coax out of the radio. I have SMA and RCA jacks that I could mount on the back of the radio. Just not sure where.

If you have any thoughts, I'd be happy to hear them. Thanks

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