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.
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.
This text simply compares several SDCards I own regarding speed. I use the cool tool “gnome-disks” to do the testing.
In following image, a defect (?) SD card, that was used in a Raspberry as (only) disk. ON that Raspberry, a (seldom used) Kubernetes cluster was running.
Card is a Sandisk Ultra 32GB , class 10, A1.
Upper card: the broken Sandisk card, lower card, the Samsung, low write speed, but still considered ok
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…
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…)
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.
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.
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.
East german product. With tube technology. From 50ies. Obsolete, Outdated. Unhip?
The root of all this came from Corona agony. I thought: Why not to look again to tube technology?
Device after cleanup and fixing
Last year a friend gave me an old tube radio as a gift. I love the sound of this small Lowe Opta Bella Luxus and handled it like a religious device, e.g. the Bundeslade.
Time passed and I thought: why not getting another tube radio.
M-Audio sold around 2003 this MIDI keyboard. Besides the 2 octave keyboard it offers also an external USB Sound card with many audio connections. Moreover it offers controls to control a DAW application. Target Operating System were Mac and Windows.
I got such a keyboard in 2020 and tried to use it with Linux. This is possible and I describe here what has to be done.
The connectivity between Keyboard and PC is USB, with version 1.
