Michael Kellett's Blog - All Comments

RE: PCB micro surgery.

DAB — Tue, 03 Feb 2026 20:02:28 GMT

Nice work.

Your eyesight and skills are beyond mine.

RE: PCB micro surgery.

shabaz — Mon, 02 Feb 2026 15:27:46 GMT

Nice surgery : ) C120 must be extremely tiny.. that's what is in the tweezers I presume?

I've got T210 and T245 handles, and love the range of tips.

RE: PCB micro surgery.

rsjawale24 — Sun, 01 Feb 2026 12:32:47 GMT

That's some nice SMD work!

I have been planning to switch to C245/210 style soldering station for a long time now. But not sure which station to buy. I have my old Tenma 65W station that uses the 900M style tips, a multicomp pro 120W with same style of tips and an ifixit 100W USB soldering iron. But none of them are good for SMD work.

RE: Measuring DC-DC converter Efficiency

supercachai — Fri, 07 Nov 2025 20:34:17 GMT

Great post, thanks for the write up.

Did you consider using the Riedon PCS series? They are in a similar price range as RSN, but THT and can be mounted on a heat sink. So you can achieve a much better thermal coupling, which will probably eliminate any temp drift.

I am building something similar for currents up to 40 A so heat can lead to significant drift, especially when current ratios are very different.

RE: FNIRSI SAG-55 Hot Air Gun

DAB — Thu, 10 Jul 2025 21:41:35 GMT

Nice review.

I doubt I will buy one, but it is nice to keep up with the current technology.

RE: FNIRSI SAG-55 Hot Air Gun

shabaz — Thu, 10 Jul 2025 17:24:35 GMT

It looks really nice. And as you say the Atten is much larger, it takes up a lot of desk space due to the thick hose, so the SAG-55 is more attractive in that respect as well as the price. I have nozzles for a different hot air station which are commonly available from AliExpress, so if anyone wants me to measure the dimensions in case they might fit the SAG-55, let me know.

RE: FNIRSI SAG-55 Hot Air Gun

genebren — Thu, 10 Jul 2025 15:07:23 GMT

This sounds very promising. I am still awaiting the arrival of mine, but it will interesting to see how I feel about it when it gets here.

I have been looking around for more nozzles, but I have decided to wait until I use it a bit before I start accessorizing it. Thanks for the update!

RE: Two rather different communications testers.

DAB — Thu, 22 May 2025 19:16:04 GMT

Nice find.

It will be interesting to see if they still work and what you do with them.

RE: Two rather different communications testers.

JWx — Tue, 20 May 2025 17:05:31 GMT

I wonder what clocking sources are used in them? Typical quartz oscillators or something more advanced/expensive (especially for clock quality measurements)?

RE: Two rather different communications testers.

Jan Cumps — Tue, 20 May 2025 17:03:01 GMT

Some good data points on running a business here.

We probably made between 150 and 250 of them and I think they were sold for about £350. It might have been a little more but certainly no more than £500.

If we take the best case in those days: 250 units sold, £500 each.
Did this product generate a viable profit? Enough to cover R&D, BOM, production, and expected margin?

RE: RT1-M Digital Audio Analyser

DAB — Sat, 10 May 2025 18:57:53 GMT

Nice find, they should give you lots of fun just checking them out.

RE: RT1-M Digital Audio Analyser

shabaz — Tue, 06 May 2025 15:39:53 GMT

Wow looks like a stunning piece of equipment. Definitely a bargain. Hehe I too found it surprising that even 1 rack-unit equipment can be deceptively weighty. I have a 1RU full-depth server that is crazy-heavy (sadly not powered up often because of the fan noise that makes).

RE: Fixing an HP59313A

DAB — Mon, 05 May 2025 19:14:13 GMT

I remember the old HPIB well.

Powerful in concept, but a pain in the ass to program.

RE: Fixing an HP59313A

shabaz — Mon, 05 May 2025 17:25:51 GMT

Nice-looking hardware! Definitely fun exploring what's inside old equipment. A lot of the vintage stuff had so much logic ICs the boards are huge. I also liked this example of fitting in the boards (image source) to still allow for troubleshooting:

There's one on ebay currently, but too expensive (I already at a high level know how this thing works, although it would have been fun to explore since there's a ton to learn from it). It's a speech encryption device that plays with the signal in ways such as flipping the frequency spectrum and chopping the speech samples into segments and swapping the order, and so on.

RE: Measuring DC-DC converter Efficiency

Jan Cumps — Tue, 04 Feb 2025 19:34:36 GMT

> I have a DAQ970 system with a solid state multiplexer

Do you have this one: DAQM900A 20-Channel FET multiplexer module?