elektronik

Converting a DEC Keyboard LK401 to a USB Keyboard

Spurtikus
DEC Keyboard LK401 has serial interface, 4800 Baud, 8N1. See more information on the keyboard hardware here. The keyboard is heavy, has nice keys and is of the old 80ies quality. 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. Possible Controllers: Arduino e.g. Arduino Micro Teensy Raspberry e.

DEC LK401 Keyboard

Spurtikus
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. I tried to convert this keyboard into an USB keyboard, see here. An Intel 80C51 microcontroller handles most of the keyboard functions We can see also the Beeper and a 7.3728 MHz Quartz Beeper, a 7475 and two LEDs. Datecode of 7475 is 29th week 1992

Experimenting with an old FM tuner

Spurtikus
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

Spurtikus
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

Spurtikus
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

Spurtikus
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)

Spurtikus
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

Spurtikus
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

Spurtikus
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.

Radio Loewe Opta Komet 53

Spurtikus
I bought this radio as defect, does not play for some euros. It had no power plug anymore, and my initial idea was to tear it apart to salvage the ancient parts used in the 50ies. Radio after minor repair work The wooden case was in quite good condition and all switches and knobs were present. So I decided to check for the issues in the radio and maybe repair it.