Banner for Heathkit SB-620 frequency conversion article

The Heathkit SB-620 “Scanalyzer” is an IF spectrum analyzer. It graphs the amplitude of signals around the one that your receiver is looking at, so you can see all of the signals around you at a glance. Problem is, it has to be setup for the particular IF frequency of your receiver. The original kit included parts for a wide range of IF frequencies. Only one frequency could be installed though and my unit had the wrong frequency for the classic Heathkit SB-301 receiver I have.

The pdf article describes how to convert it to the IF frequency common to many Heathkit receivers, including: SB-100, SB-101, SB-110, SB-102, SB-104, SB-300, SB-301, SB-303, HW-100, HW-101 and HW-104. The photo above shows it operating with actual 80m signals. Get the article and schematic below:
Converting the Heathkit SB-620 icon

Converting the SB-620 article (1.8MB)
New IF booster amp and coils in the Heathkit SB-620

IF booster amp and  new coils in the SB-620

 

Reader Comments

Posted by Steve L. April 05, 2022 - 05:52 pm
Hi Rick, Congratulations on completing the kit and the mod! Seeing the signals too high, even with the PIP gain all the way down suggests that the signal from the receiver is going to the RF Input. Rather, it should go to the IF Input. The Ham Scan switch on the back should be UP to select Ham Scan. (The way Heath has that designed and labeled seems confusing.) The Amplitude Scale switch should be set to LOG. I doubt you will need the trimmer caps unless you end up scratching for more gain. Please let us know how that goes. We'll get to the bottom of this!

Posted by Rick April 05, 2022 - 03:04 pm
A few years ago I was lucky enough to purchase a complete 620 kit! Over the past winter I completed and aligned the kit for my SB 102 and it worked. However, only the stronger signals seemed to pop up...couldn't see the noise level at all. I cam across this article about the pre amp and thought this might do the trick. I completed the amp and was now wondering if I need the trimmer caps or since I used the original coils for the 3395 IF I didn't need them. I hooked up the pre amp and signals are now too high even with the PIP gain all the way down. Haven't realigned anything yet with the pre amp.

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

Steven


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