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I always am amazed by how chaotic point-to-point wiring is. Diodes hanging here, a capacitor there, with no real sense of organization. It's such a contrast from the ordered appearance of a PCB.
Nice. I repair and restore vintage tube amps as hobby. Good distraction from software and modern tech
If you like this, you’ll probably like this restoration of these old headphones https://youtu.be/98pUBuTar_s
I was like: how related is one really to the other, but you pulled me into that one. Now I have a different question: how much of an old artifact do you need to retain to still call it a "restoration", as opposed to a "replica"? (I realize this is not a question unique to this video.) Very skillful, though! And the video style is very... soothing :)
Just a word of caution: isn't working with tubes dangerous, due to the high voltage?
This particular radio appears to have an isolation transformer which makes it somewhat safer, but some older tube radios are actually connected directly to the mains line with no isolation transformer (this was done to save costs).
Those are especially dangerous to prod around in without the proper safety precautions when they are turned on, or even just plugged into the wall.
I have a friend I help out who does this type of thing. We're currently working on some ART-13 Transmitters, which were used in WWII bombers and feature a then-secret technology called "autotune" which is a mechanical way to pre-set all the knobs to known positions at the flick of a switch. It's been quite an interesting journey. BTW: Autotune does NOT actually tune the antenna network for maximum output, etc.
Those tank transceivers were fm so they are not much of use today. That's one https://en.wikipedia.org/wiki/R-123
One of more popular devices still hunted and used by radio amateurs in countries in the region is the vacuum tube power amplifier for the big KF military radio R-140m. Unfortunately there is little info in English about it. It looked like this http://www.r140.de/
In modern times there is a control box made by some amateur that can be used to program auto tune presets in the R-140m linear amplifier. It actually tunes the antenna's network too.
Just a word of caution: isn't working with tubes dangerous, due to the high voltage?
Yes it is. This particular radio appears to have an isolation transformer which makes it somewhat safer, but some older tube radios are actually connected directly to the mains line with no isolation transformer (this was done to save costs). Those are especially dangerous to prod around in without the proper safety precautions when they are turned on, or even just plugged into the wall .
- All an isolation transformer (which is an external component you have to supply; it's never part of the radio) does is make the mains AC voltage inside the radio "float" in contrast with the voltage coming from the wall outlet (which is of course referenced to the actual ground outside your house). This makes things a little safer because if the chassis becomes live for any reason then there won't be a potential difference between the chassis and the ground that you're standing on, meaning you won't suddenly find yourself forming part of the circuit if you touch the chassis. In these old radios it's super easy for the chassis to become live so this is a good precaution.
- Isolation transformers do nothing for safety concerning the dangerously high DC voltages which the tubes run on. In the amp itself, the AC voltage comes in, hits a power transformer inside the amp (to get nice high voltages for the tubes), then is rectified into DC, then goes into the circuit to drive the tube plates and do all the other stuff it has to do. You can still get an almighty and quite easily fatal zap if your body provides a path between high DC voltage and the chassis (which is also the DC ground). Hence the rule, only work with one hand in a powered-on amp, because at least that way if you touch something then 350V of DC can't travel up one hand, through your heart, and back out the other arm.
- The final thing you might be referring to ("some older tube radios...") around cost savings is the archaic practice of skipping the power transformer entirely and connecting the wall AC voltage directly to the rectifier. This requires various compromises in the circuit (the DC voltage produced is quite low) and you _have_ to connect these with an isolation transformer or you're really asking for trouble - the chassis is all but guaranteed to be live. The original makers in the '40s and '50s, at least keen to be seen to try to avoid killing their customers, "solved" the problem by using plastic control knobs. Here's a good article: https://antiqueradio.org/safety.htm
A refurb article on the exact same model is a sign from the thermionic gods that I have to get it on my workbench and fix it up.
Earlier quoted context omitted.
Yes it is. This particular radio appears to have an isolation transformer which makes it somewhat safer, but some older tube radios are actually connected directly to the mains line with no isolation transformer (this was done to save costs). Those are especially dangerous to prod around in without the proper safety precautions when they are turned on, or even just plugged into the wall .
Just to be pedantic (I think it's ok given the venue...) - All an isolation transformer (which is an external component you have to supply; it's never part of the radio) does is make the mains AC voltage inside the radio "float" in contrast with the voltage coming from the wall outlet (which is of course referenced to the actual ground outside your house). This makes things a little safer because if the chassis becom…
Yes, you can still receive a fatal shock via one arm to the other even with an isolation transformer.
It's not true to say that it does nothing for safety, though. It provides isolation vs ground and prevents the circuit from being completed through your feet and the floor:
https://electronics.stackexchange.com/questions/17496/how-is...
It also limits the total current to whatever the transformer can supply before voltage starts to sag.