Voice Control For A Vintage Heathkit Radio

Most modern ham rigs have a voice activated transmission (VOX) mode, although we don’t know many people who use it often. When a transmitter is in VOX mode, it starts transmitting when you talk, and then, when you pause for a second or two, the transmitter turns off. Many old ham transmitters, though, didn’t support VOX, so Heathkit sold the VX-1 “electronic voice control” to add VOX to older transmitters. [Jeff Tranter] shows us inside a clean-looking unit.

These devices were sold from 1958 to 1960 and used tubes and a selenium rectifier. The device is connected between the microphone and the transmitter. It also sat between the receiver and the speaker to mute audio while transmitting. The original unit had a screw terminal to connect to the outside world, and some of the screws had live line voltage on them. The unit [Jeff] examines is modified to have phono jacks along with a few other repairs.

The wiring looks like a tube radio. Tubes are above the chassis, and point-to-point wiring is underneath. There is also an unusual sealed selenium rectifier. [Jeff] shows how the device works using just a receiver. A few minor repairs were needed.

If you are interested in getting your ham license, most modern radios support VOX out of the box — no rhyme intended. We do, however, love that old Heathkit gear.

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A Dusty Boat Anchor Back From The Brink

Many of us will have found dusty forgotten pieces of electronics and nursed them back to health, but we were captivated by [Don]’s tale of electronic revival. Instead of perhaps a forgotten computer or television, his barn find was a Heathkit linear amplifier for radio amateurs. In that huge box underneath an impressive layer of grime were a pair of huge tubes, along with all the power supply components to give them the 2 kV they need. It should have been good for a kilowatt when new, can it be made to go on air again?

Perhaps understandably with such an old device, after cleaning away the dust of ages he replaced the power supply circuitry with new parts and PCBs. A linear amplifier is surprisingly simple, but because of the voltages and power concerned there’s a need to treat its power circuits with respect. On first power-up the filaments work and the rails come up, so when given some RF drive it comes alive. Coupled with a case restoration you’d never know how dreadful a state it had been in.

We like to see classic Heathkit devices here at Hackaday, though we’ve followed their more recent reappearance too.

Magnetic Bubble Memory Brought To Life On Heathkit

There are all kinds of technology that appear through the ages that find immediate success, promise to revolutionize the world, but fade to obscurity almost as quickly. Things like the ZIP disk, RDRAM, the digital compact cassette, or even Nintendo’s VirtualBoy. Going even further back in time [smbaker] is taking a look a bubble memory, a technology that was so fast and cost-effective for its time that it could have been used as “universal” memory, combining storage and random-access memory into a single unit, but eventually other technological developments overshadowed its quirks.

[smbaker] is placing his magnetic bubble memory module to work in a Heathkit H8, an Intel 8080-based microcomputer from the the late 70s. The video goes into great detail on the theory of how these devices used moving “bubbles” of magnetism to store information and how these specific devices work before demonstrating the design and construction of a dedicated support card which hosts the module itself along with all of the necessary circuitry to allow it to communicate with the computer. From there he demonstrates booting the device using the bubble memory and performs several write and read actions using the module as a demonstration.

Eventually other technologies such as solid-state RAM and various hard disk drives caused the obsolescence of this technology, but it did hang on for a bit longer in industrial settings due to its ability to handle high vibrations and mechanical shocks, mostly thanks to the fact that they had no moving parts. Eventually things like Flash memory came around to put the final nail in the coffin for these types of memory modules, though. The Heathkit H8 is still a popular computer for retrocomputing enthusiasts nonetheless, and we’ve seen all kinds of different memory modules put to work in computers like these.

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Retro Gadgets: Make Your Scope Dual Channel

We live in a time when having an oscilloscope is only a minor luxury. But for many decades, a good scope was a major expense, and almost no hobbyist had a brand new one unless it was of very poor quality. Scopes were big and heavy and, at the price most people were willing to pay, only had a single channel. Granted, having one channel is better than having nothing. But if the relative benefit of having a single channel scope is 10 points, the benefit of having two channels is easily at least 100 points. So what was a poor hacker to do when a dual-trace or higher scope cost too much? Why, hack, of course. There were many designs that would convert a single trace scope into a poor-quality multichannel scope. Heathkit made several of these over the years like the ID-22, the ID-101, and the ID-4101. They called them “electronic switches.” The S-2 and S-3 were even earlier models, but the idea wasn’t unique to Heathkit and had been around for some time.

For $25, you could change your scope to dual trace!

There were two common approaches. With alternative or alt mode, you could trigger a sync pulse and draw one trace. Then trigger again and draw the second trace with a fixed voltage offset. If you do this fast enough, it looks like there are two traces on the screen at one time. The other way is to rapidly switch between voltages during the sweep and use the scope’s Z input to blank the trace when it is between signals. This requires a Z input, of course, and a fast switching clock. This is sometimes called “chopper mode” or, simply, chop. This wasn’t just the realm of adapters, though. Even “real” analog scopes that did dual channels used the same methods, although generally with the benefit of being integrated with the scope’s electronics.

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A PDP 11 By Any Other Name: Heathkit H11 Teardown And Repair

[Lee Adamson] is no stranger to classic computers. He recently picked up a Heathkit H11A which, as you might remember, is actually a PDP-11 from DEC. Well, technically, it is an LSI-11 but still. Like a proper LSI-11, the computer uses the DEC QBus. Unlike a lot of computers of its day, the H11 didn’t have a lot of switches and lights, but it did have an amazing software library for its day.

[Lee] takes us through a tour of all the different cards inside the thing. It is amazing when you think of today’s laptop motherboards that pack way more into a much smaller space. He also had to fix the power supply.

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Heathkit IM-13 VTVM Repair

If you are under a certain age, you might not know the initialism VTVM. It stands for vacuum tube voltmeter. At first glance, you might just think that was shorthand for “old voltmeter” but, in fact, a VTVM filled a vital role in the old days of measuring instruments. [The Radio Mechanic] takes us inside a Heathkit IM-13 that needed some loving, and for its day it was an impressive little instrument.

Today, our meters almost always have a FET front end and probably uses a MOSFET. That means the voltage measurement probes don’t really connect to the meter at all. In a properly working MOSFET, the DC resistance between the gate and the rest of the circuit is practically infinite. It is more likely that a very large resistor (like 10 megaohms) is setting the input impedance because the gate by itself could pick up electrostatic voltage that might destroy the device. A high resistance like that is great when you make measurements because it is very unlikely to disturb the circuit you are trying to measure and it leads to more accurate measurements.

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VCF East 2021: Preserving Heathkit’s 8-Bit Computers

To say the Heathkit name is well known among Hackaday readers would be something of an understatement. Their legendary kits launched an untold number of electronics hobbies, and ultimately, plenty of careers. From relatively simple radio receivers to oscilloscopes and televisions, the company offered kits for every skill level from the post-war era all the way up to the 1990s.

So it’s hardly a surprise that in 1977, seeing the success of early home computers like the Altair 8800 and IMSAI 8080, Heathkit decided to join the fray with a computer kit of their own. But by that point the home computing market had started to shift from a hobbyist’s pursuit to something the whole family could enjoy. Compared to the Apple II and TRS-80, both of which also launched in 1977, Heathkit’s machine seemed like the product of a bygone era.

While it might not have gained the notoriety of the microcomputers it was designed to compete with, the Heathkit H8 is certainly not forgotten. Tucked away in a corner at the 2021 Vintage Computer Festival East was an impressive exhibit dedicated to the Society of Eight-Bit Heath Computerists (SEBHC) called Heathkit: Keeping the Legacy Alive. Presented by Glenn Roberts, this collection of original and modern hardware demonstrated the incredible lengths to which this group of passionate Heathkit owners have gone to not just preserve the memory of these often overlooked computers, but to continue to improve upon the kit’s unique design.

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