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Showing posts from July, 2020

Thermionic Valve Power Supply

Tinker, Tailor, Soldier, Sailor I like to tinker with old fashioned thermionic valve circuitry - tubes, for the 'Merrykins.  It is strangely crude and simple and they make a friendly orange glow in the evening.  However, powering the things is hard, due to the high voltages that are required to overcome the vacuum. The below picture shows how I build these toys.  It happens on the fly.  This is a hobby, so I don't kill myself with design calculations.  The tag strips enable experimentation to adjust things till it works properly.  The VU Meter even has a little transistor in there - sheer desperation! Transformerless Valve Power Supply One can use transformers, but they are big, heavy and expensive and shipping hunks of metal around the world make it even more so.  It makes sense to use transformers if you build a high power circuit with multiple valves, such as a guitar amplifier, but a small circuit with only one or two valves presents a problem.   For a small fun display pro

C-Band Yagi Antenna

A Formal Bow Tie Event I have made a few PCB antennas and the Yagis worked well, but they were very narrow band.  So I tried to improve that by making the elements conical - or in this case, since it is 2D PCB antenna, triangular. I think it is a fairly unique idea and I certainly haven't seen a picture of a PCB antenna like this before.  The Driven element and first director are flared to 3 mm (since there is no more space) and the Reflector and other Directors are flared to 10 mm. Wide Band Yagi with Unbalanced Co-ax Feed I'll see what happens once the conformal coating dried and I hooked up a cable. It is the same design I used before - I just flared the elements and left out the last 2 directors: This way I can compare the two antennas with each other.  I didn't bother to simulate it - I just went ahead and machined it to see what happens. Antenna Gain Initial tests showed that the gain is about 5 dBi which is typical for a 5 element Yagi and the bandwidth of the new an

Bar Clamp

Clamped Up I needed a little clamp, but we were in Covid19 lock down.  So I made one.  No transistors, no batteries, no thermionic valves, no flashing neon bulbs! There are many complicated ways to make a bar clamp, but I prefer the simple way.  A picture is worth a thousand words: Mini Bar Clamp It can't be simpler: One 6 mm dowel rod One 6 x 80 mm bolt One 1" nail Ten popsicle sticks Glue Yup - ten popsicle sticks glued together, made a small piece of plywood, that I could cut up for the clamp jaws.  You can use the exact same method to make a big bar clamp.  You don't need a super long lead screw, just a long bolt and a whole lot of little holes to adjust the other end of the clamp.  Scale it up as required for size and strength. How do I keep the movable jaw in place?  Some funny putty (Press Stick) in a hole.  It churns around in there and keeps the block from falling off the end of the bolt - a little piece of rubber will also do.  The best wa