Converting a DEC Keyboard LK401 to a USB Keyboard
DEC Keyboard LK401 has serial interface, 4800 Baud, 8N1. See more information on the keyboard hardware here. The keyboard is solid and heavy, has superb tactile keys and is of the old 80ies quality. That you simply cannot order on Amazon or so. For a long time, the keyboard was supported by the Linux kernel, but this time is gone. My idea: connect the keyboard to a microcontroller that can connect to a PC via USB.
DEC LK401 Keyboard
This keyboard came in as part of a Digital DEV VT402 terminal. I have some information on that terminal here . After some time, I found that the keyboard of that terminal is also an interesting kind of thing. DEC LK401 Hardware DEC Keyboard has a serial interface. The connector to plug into a DEC VT420 terminal looks like an old telephone connector, with 4 pins, called RJ10. An Intel 80C51 microcontroller handles most of the keyboard functions We can see also the Beeper and a 7.
Experimenting with an old FM tuner
I tried to buy a variable capacitor via ebay. What I got was the variable capacitor together with a small metal box. The box contains a FM tuner. It contains two germanium transistors AF121/AF125 and it seems it is from the 1960ies. (click to view larger version) This picture shows the variable capacitor, forming the base for the FM tuner. Metal box has been removed. I was not able to move the shaft/axis of the capacitor.
Modulation and Demodulation - HF-Probe
When searching for a scheme for a HF probe, I found a good working solution at https://elektronikbasteln.pl7.de/signalverfolger-fuer-nf-und-hf-selbst-gebaut . The scheme uses two germanium rectifiers and looks like this: (click to view larger version) My hand drawing, a better image can be found on https://elektronikbasteln.pl7.de/signalverfolger-fuer-nf-und-hf-selbst-gebaut I tried that HP probe schema with good results. The original uses 2 diodes AA118, I have used AA143. In the next images, we can see a 25 MHz signal, AM-modulated with a 1 KHz signal.
Tube Meter Heathkit IM-18D
Since the 1950ies, Heathkit produced tube voltmeters. The Heathkit IM-18D is one of these, more from the 60ies, but I do not know the exact production year of my device. Heathkit sold these devices as kits. So you got all parts and soldered it all together. Also calibration was left to the buyer. You can compare this tube meter with my Heathkit V-7A, which is about 10 years older but very close…
Tube Meter Heathkit V-7A
When buying my Heathkit IM18D (see here), I got this meter for a few more bucks. It was very dirty and was sold as not working. Also, someone has poured some silver paint over the poor device… Heathkit V-7A after some cleaning (knobs were in dishwasher when I took that photo) Some strange kind of line connector was found (this is a DIN connector, and I suppose someone had a cable that was used to put 230 volts in here…)
Grundig SV41 Signalverfolger (signal tracer)
When entering the area of old tube receiver repairment, I found that a signal tracer device is crucial. With this device, you can trace a signal in the stages of the radio device and identify the stage that is not working anymore, so it is a great tool to troubleshoot radio receivers. Grundig SV41 signal tracer Signal tracers are not produced anymore, I think they passed when receivers and amplifiers were designed with ICs, where you have multiple or all stages of an electronic circuit in a single chip.
Hickok 539A tube tester
Having 3 tube radios from 1950 .. 1960ies, I though it’s time to also have a tube tester. You can have the simple ones, but also a lab level device. All these tube testers come from 1950 .. 1960 years. You can have one for european tubes only or more general ones with american and european tubes. So I decided to get an american version. All modern amplifier tubes are american brand, so this is a good approach.
NEVA Netzgleichrichter for experimenting with Tubes
To experiment with tubes, a power supply that creates higher voltages is required. Most lab power supplies supply up to 30, maybe 50 volts, some older ones may even go up to 100 volts. While tubes operate already somehow at these values, for testing etc., I looked for a real tube power suppy. I found one from an older german company, called NEVA. As far as I can see, they mostly produced for universities and school labs.