Variometers with nested solenoids are fun and pretty easy to make, you can use them for coupling adjustment in regenerative receivers too. A super simple SW regen would be a variometer tank wound on a nesting pair of cardboard tubes with adjacent tickler also pivoted to rotate, a small fixed capacitor (maybe switched or tap the tank coil), an RF JFET, a resistor or two, a bypass cap, battery and a crystal earphone. Antenna tuning and coupling might also be a variometer. Homebrew variable capacitors are quite practical. Sliding and telescoping geometries are the easiest, but rotary can be made too. Cutting the plates isn't much fun I'll admit, especially for larger capacitance, but you can even use a plastic substrate and Aluminium or Copper tape to cover them. A laser cutter makes short work of it, but a hole saw or even scissors could be used. Add some threaded rod and hardware and assemble as many plates as you need. For high-Q use like transmitting variables you can use brass and silver plate it, split the stator and eat the halving of the capacitance, but eliminate sliding contact loss. An alternative geometery I made a video about a while ago is a spiral wound compression-style variable. Not very stable or practical to calibrate, but very easy to build with Copper or Aluminium tape or roofing flashing foil. The dielectric can be low loss polymer film like PP or PET. Paper or PE works in less demanding apps. The parasitic inductance and resistance isn't too bad for MW or LW receivers. SW would be challenging because of poor mechanical stability. A more conventional book-style compression capacitor might be used instead and while it still needs a lot of plate cutting assembly is much faster than a rotary cap.

In Aus you can get a list of all of the local council pick-ups and do the rounds on a regular basis. You are guaranteed at least a couple of variable caps per suburb and all sorts of other useful stuff.

Peter, one trick you can use to cut down on wind sound (and attenuate the audio level slightly) is to wrap a little scrap of soft foam such as the kind you might find in an equipment case or inside a cushion/mattress around the mic. The best option is fake fur or similar, which if you can find a scrap piece from a garment at an opp shop or similar, it will work wonders. You can tape or use a tiny cable tie to secure the material around the mic.

Useful information indeed.

I like the MVAM109 varactor, 40 to 420pF. Getting hard to get these days but still listed at a few US suppliers. Maybe Permeability Tuned Oscillators will make a comeback.

i cant find AM variable caps(160p) or IFTs anymore in local market,but there are plenty of FM variable caps (22p) there.

Wew, good thing I have a lot of them on stock, new and used salvaged from old radios.

I think they already stopped making variable capacitor. I tell that because it is practically impossible to find variable capacitors here in Fortaleza-Ceará-brasil. lol But thanks God they have invented the DIODE VARICAP!!!!

I also saw a Spanish video where a guy made a tuning capacitor out of rotating metal plates from scratch. I wish I had written the title of the video at the time, but I forgot. I'm sure the video is still there on KZfaq.

Nice video, but I think they'll be around in the trash for a while. At the moment I won't even use one in a project unless it's pre-70's and all metal :)

Those variable capacitors are perfect thing. I like them.

alternative for variable caps is a variometer coil. i build regenerative fet receiver without variable caps, i use double variometer coils , similar than aeriola sr receiver in 1921s

Very good 73 from baghdad de Yi1hxh .

Some stochy diodes and power transistors work well as a varicaps... using 0-9V tuning voltage... power diodes gives 500...150pF and transistors 1000....250pF tunning capacity range... all this devices from impule power supply.... or junk box....

They are still making small runs of the old air var caps for some suppliers

I won't miss them.They are lossy,and have a high temp.coefficient.You cannot use them in a vfo.-73 PZ1CD.

They aren't going anywhere. Every alarm clock uses one. We will always need to wake up.

we should be ok. there is plenty out there

I guess we will build our own or switch to varicaps.

Plenty available new, direct from China on ebay and via other sources, so I think I will be ok..

maybee ask Dick Smit?

Where are you from? You pronounce almost all the vowels as "a". "capacitah", "anadah posibility", "receivah"... Automatic translation is wrong because of that. Thanks for great videos.

No big loss, as they are of very poor quality!!