They say you can buy anything on the Internet if you know the right places to go, and apparently if you’re in the mood to make diamonds, then Alibaba is the spot. You even have your choice of high-pressure, high-temperature (HPHT) machine for $200,000, or a chemical vapor deposition (CVD) version, which costs more than twice as much. Here’s a bit more about how each process works.

Of course, you’ll need way more than just the machine and a power outlet. Additional resources are a must, and some expertise would go a long way. Even so, you end up with raw diamonds that need to be processed in order to become gems or industrial components.

For HPHT, you’d also need a bunch of good graphite, catalysts such as iron and cobalt, and precise control systems for temperature and pressure, none of which are included as a kit with the machine.

For CVD, you’d need methane and hydrogen gases, and precise control of microwaves or hot filaments. In either case, you’re not getting anywhere without diamond seed crystals.

Right now, the idea of Joe Hacker making diamonds in his garage seems about as far off as home 3D printing did in about 1985. But we got there, didn’t we? Hey, it’s a thought.

Main and thumbnail images via Unsplash

It is common these days to have a soldering iron where you can set the temperature using some sort of digital control. But how accurate is it? Probably pretty accurate, but [TheHWCave] picked up a vintage instrument on eBay that was made to read soldering iron temperature. You can see the video below, which includes an underwhelming teardown.

The device is a J thermocouple and a decidedly vintage analog meter. What’s inside? Nearly nothing. So why did the meter not read correctly? And where is the cold junction compensation?

The probe seemed okay when used with a modern meter. However, driving the meter directly showed a problem. It seemed like something was wrong with the meter’s movement.

Pulling the meter out revealed a handwritten label identifying the meter as having a full-scale deflection of just over 27 millivolts and using a 0.5 ohm external resistor. Unsurprisingly, the old meter had some issues with the thermocouple.

Pulling the meter showed that the compensation was actually inside the meter casing. The meter’s problem was due to these extra components: an NTC thermistor and a custom wire-wound resistor. Changing the resistor fixed the box. This time, he put the two components outside the meter housing in the vast space of the nearly empty case.

Today, we take measuring temperature for granted. Only the cheapest meters lack temperture measurement and you can use other techniques like IR sensors, too. But this was an interesting look at how it was done “back in the day” and an interesting repair, too.

Thermocouples are an old standby for measuring high temperatures. With modern tech, it is pretty simple to compensate them.