A Switching Power Supply, 1940s-Style

“They don’t build ’em like they used to.” There’s plenty of truth to that old saw, especially when a switch-mode power supply from the 1940s still works with its original parts. But when said power supply is about the size of a smallish toddler and twice as heavy, building them like the old days isn’t everything it’s cracked up to be.

The power supply that [Ken Shirriff] dives into comes from an ongoing restoration of a vintage teletype we covered recently. In that post we noted the “mysterious blue glow” of the tubes in the power supply, which [Ken] decided to look into further. The tubes are Thyratrons, which can’t really be classified as vacuum tubes since they’re filled with various gasses. Thyratrons are tubes that use ionized gas – mercury vapor in this case – to conduct large currents. In this circuit, the Thyratrons are used as half-wave rectifiers that can be rapidly switched on and off by a feedback circuit. That keeps the output voltage fixed at the nominal 140V DC required by the teletype, with a surprisingly small amount of ripple. The video below is from a series on the entire restoration; this one is cued to where the power supply is powered up for the first time. It’s interesting to see the Thyratrons being switched at about 120 Hz when the supply is under load.

Cheers to [Ken] and his retrocomputing colleagues for keeping the old iron running. Whether the target of his ministrations is a 1974 scientific calculator or core memory from an IBM 1401, we always enjoy watching him work.

Continue reading “A Switching Power Supply, 1940s-Style”

Ancient Teletype Revived in Labor of Retrocomputing Love

Readers with not too many years under their belts may recall a time when the classic background sound effect for radio and television news programs included a staccato mechanical beat, presumably made by the bank of teletype machines somewhere in the studio, clattering out breaking stories onto rolls of yellow paper. It was certainly true that teletypes were an important part of the many communications networks that were strung together over the 20th century, but these noisy, greasy beasts had their day and are now largely museum pieces.

Which is exactly where the ancient Model 19 Teletype machine that [CuriousMarc] and company are restoring is destined. Their ongoing video series, six parts long as of this writing, documents in painstaking detail how this unit worked and how they are bringing it back to its 1930s glory. Teletypes were made to work over telephone lines with very limited bandwidth, and the hacks that went into transmitting text messages with a simple 5-bit encoding scheme are fascinating. The series covers the physical restoration of the machine, obviously well-loved during its long service with the US Navy. Of particular interest is the massive power supply with its Thyratron tubes and their mysterious blue glow.

The whole series is worth a watch if you’re even slightly interested in retrocomputing. We’re particularly taken with the mechanical aspects of these machines, though, which have a lot in common with mechanical calculators. [Al Williams] recently covered the non-replacement of the power supply caps for this unit, which is an interesting detour to this restoration.

Continue reading “Ancient Teletype Revived in Labor of Retrocomputing Love”

A clock made out of some very weird tubes

If you’re like [Richard], you’ve got a few really rare components lying around. Maybe it’s a very weird micro or a really tiny CRT, but eventually you’ve got to build something with these parts. When [Richard] decided to put some ITS1A neon display tubes to use, he fell back to the old standby – a really awesome clock.

Unlike the lowly Nixie tube, the ITS1A tube is weird. It’s a neon seven-segment display that can be controlled directly from the pins of a microcontroller. It does this with the help of seven tiny thyratrons in each segment. Even though this tube has neon, the display isn’t the familiar neon orange-red. The tube emits a lovely green with the help of a phosphor coating.

With a single digit already incorporated into [Richard]’s clock, he needed four indicators for the hours and minutes. After a failed experiment with a crazy 4-color, 16-pixel Melz ITM2-M display, he moved on to a simpler MTX90 thyratron indicator.

Using the same control scheme as his earlier numitron clock, Richard had a PCB made and wired everything up. The seven-segment tube indicates the value, and the indicator tubes indicates the position of the digit in the XX:XX standard. A very cool  build with parts you don’t see coming around often.