Friday, July 24, 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 project using Nixie, Magic Eye or VFD tubes, you certainly don't want a huge box with a heavy transformer.  However the project should be self contained, with nothing else connected to it.  Rather don't put a headset on a valve amplifier!

VU Meter Top Panel

This article describes how to build a reactive heater supply and a rectified mains high tension supply, that will not break the bank, or your back, or risk burning your house down.

The problem is that the mains supply is 'dirty'.  The Earth wire sometimes isn't earthed.  The Neutral and Live wires can be swapped.  There can be high voltage spikes caused by air conditioners, industrial machinery and lightning.  So if you want your circuitry to last longer than a few months, then you need to protect it carefully.  You can either use a big hunk of transformer iron and copper to provide the protection, or you can use a few carefully selected specialized components, to do that with a little more finesse.

Circuit Protection

You should combine the two circuits below after the choke.  I drew them separately to make it more clear.

Safety Capacitors
A Safety Capacitor is self healing and self extinguishing.  If it gets zapped by a high voltage spike, then it will carry on working despite the puncture.  Eventually, the capacitor may fail, but while it may smoke, it will not burst into flames and burn your house down.  They are expensive, but rather cheaper than a new house.  It is the big blue block in the picture.

Polyfuse
A polymer fuse typically contains little spheres of metal inside a rubber compound.  Normally the spheres make contact and the fuse conducts.  When it heats up, the rubber relaxes and the spheres lose contact, interrupting the current.  When the device cooled down, it will again conduct.  In case of a fault, it will cycle on/off.  In an extreme failure, it will melt permanently and open the circuit.  You absolutely must use a fuse.  You will get shorts, arcs, or blown parts from time to time, when working with high voltages.

Common Mode Choke
A common mode choke will block current spikes that are the same phase on both the live and neutral wires - for example lightning induced spikes.  There are two ways to wind a common mode choke: 
1. Double up some thin hookup wire and feed it through a toroid ten to twenty times, but then it is prone to arc between the two windings - it is easy to damage the wire coating while winding on a toroid with sharp edges (some toroids are really dreadful).
2. Make two separate windings on the 'left' and 'right' sides of the toroid for beter isolation. Start on the outside and dive into the middle - keep going.  It seems to be opposite, but it is not, the two windings rotate the same way. 

To hold the windings, drop the toroid onto a sharpened pencil held upright in a vice, then glue it with epoxy or a drop of varnish.

Gas Arrestors
Place a gas arrestor between both Live and Neutral to Ground.  A gas arrestor is a non-linear device (it is a special neon bulb).  A high voltage spike will cause the gas to form a plasma and conduct. It will continue to conduct, until the voltage subsided.  In the extreme, it will arc over between two sharp points.  This will absorb both common and differential mode spikes on the mains wires.  You can get centre tapped ones and single ones - your choice.  

You can also use a couple of zinc oxide MOVs, but since we are talking about vacuum tubes, gas arrestors are more cool.

Turret Boards and Terminal Strips
I build olde fashioned circuits on olde fashioned Turret Boards and Terminal Strips.  These are authentic early 20th century strips of Bakelite with solder pins or eyelets https://www.digikey.com/product-detail/en/tubedepot/534-831/2197-534-831-ND/10488281

Building on these strips is error prone.  This time I managed to solder a resistor directly accross live and neutral - it made a nice flash.  So it is good to have a self resetting Polyfuse.  If you prefer glass tube fuses, be sure to have a dozen available, since they only give you one shot at a mistake!

Heater Current Supply

The heater supply uses a ballast capacitor to drop the excess voltage, without generating heat as you would with a series resistor. This is a nifty trick which is rather smaller than the smallest available 6V3 transformer, but your need to get a capacitor that is designed for the purpose and it is therefore much bigger and more expensive than a garden variety capacitor.  They are known as Safety Capacitors, or Motor Run capacitors and can continuously source AC current.

Heater voltage for two valves in series = 12.6 V
Heater Current = 300 mA



(I used an ancient manual CAD program, known as a pencil)


Mains: 220 VAC at 50 Hz
Vdrop = 220 V - 12.6 V = 207.4 V RMS 
(Yankees need to recalculate using 115 V and 60 Hz)

Capacitor impedance = 1 / 2 x Pi x f x C 

4.7 uF:
Z = 1 / 2 x 22 / 7 x 50 x 4.7 x 10^-6 = 677 Ohm imaginary

Assuming that the mains voltage is much larger than the heater voltage, we can ignore the 90 degree phase shift for the following calculations and simplify, just because I'm lazy to punch more buttons on the calculator:
Vin^2 = Vc^2 + Vh^2
Vin ~= Vc + Vh

230 V Supply:
217.4 V / 677 Ohm = 321 mA

220 V Supply:
207.4 V / 677 Ohm = 306 mA

Capacitor: 871-B32926A4475K
Safety Capacitors, 4.7uF, 10%, 350Vac, LS, 37.5mm
https://eu.mouser.com/ProductDetail/EPCOS-TDK/B32926A4475K?qs=ZxCuU5VshqBvujh9kykPlw%3D%3D
$10.13 

Initially, I did not have a 4.7 uF safety capacitor available, so at first I used five caps in parallel for the prototype, which is of course 5 times more expensive and bulky, but it took a while for the next Mouser delivery to get here.

Also put a 1 Megohm 2 Watt bleed resistor in parallel with the capacitor and a 22 Ohm, 5 W resistor in series with the capacitor, to limit the start-up current until the heaters warmed up, because the heaters are non-linear and have a much lower resistance when cold (~6.5 Ohm vs ~22 Ohm).

Test the heater supply with a 22 Ohm (one valve heater) to 47 Ohm (two valve heaters), 10 Watt resistor.  Once wired to the valves, measure the current and voltage and adjust the series resistor if necessary. The green thing next to the blue block in the picture is a 22 Ohm 5 Watt resistor (The schematic above still says 10 Ohm, but 22 Ohm, 5 Watt works better for me!).

Be sure to wire the two tube heaters in series.  When you turn the system on, the current will slowly go down and the voltage will slowly go up, as the heaters heat up and their resistance increase.  Eventually, the tubes should be glowing a nice and friendly orange and the voltage should be around 12V6 AC.  I measured up to 11.9 V AC, which is gud enuff.  If the voltage and current is way out, then you need to adjust the series resistor (don't touch it - it gets hot!).

High Tension Supply

The high tension for a typical valve circuit needs to be in the order of 100 to 300 VDC.  Valves are very forgiving - when they work, they work - and contrary to popular belief, they last for many years.  Lots of the parts on the market were 'lightly used' in a military installation for 30 or 40 years, half a century ago and they still work!

You can get the HT voltage by rectifying the European mains supply and then drop the excess with a series resistor on the valve Anode.  Use high voltage diodes with a rating higher than the protection circuitry and another safety capacitor to stabilize the voltage.  (If you live in the US of A or Canada with 115 VAC, then you need to make a voltage doubler instead.)

Note that most European plugs can be inserted any which way.  If you live in Europe, then it is probably a good idea to install two fuses, in both the L and N leads and also use a DPST toggle switch.

Mains: 220 VAC @ 50 Hz
Bridge rectifier Vht = 1.414 x 220 V = 311 VDC




Mains: 230 VAC @ 50 Hz
Bridge rectifier Vht = 1.414 x 230 V = 325 VDC

Mains: 240 VAC @ 50 Hz
Bridge rectifier Vht = 1.414 x 240 V = 339 VDC

Diode, 1000V, 1A: 1N4007 (1 off or 4 off)
863-1N4007G
https://eu.mouser.com/ProductDetail/ON-Semiconductor/1N4007G?qs=y2kkmE52mdOJ200gEKhp%2FQ%3D%3D
$0.21

Capacitor: Electrolytic, 100 uF 450 VDC
$3.44

Capacitor: Ceramic, 10 nF 1000 VDC
$0.59


I used a single diode, half wave rectifier and a 10 uF, 350 V DC capacitor for the prototype, till my Mouser order arrived.  That is the advantage of terminal boards - easy to change and fix later.

However, the 10 uF, 350 VDC electrolytic capacitor was a very bad idea.  It self oscillated, thus generating a very high voltage >1000V, with various weird and wonderful things happening as a result, but since the rest of the circuit wasn't built yet, it did not cause further damage.  

Eventually I replaced it with a Ceramic 10 nF 1000 V, paralelled with a Ceramic 1 uF 1000 V,  paralelled with an Electrolitic 100 uF 350 VDC capacitor, which calmed the HT supply down and since it now finally works, I'll just leave it like that.  How this works, is that the X rated ceramic capacitor has the lowest impedance and handles the brunt of the ripple, which is then further smoothed by the 100 uF Electrolytic and the little 10 nF in parallel with it, damps any self oscillations in the Electrolytic capacitor.

Note that you must use 2 Watt resistors to discharge the capacitor bank and drive the Neon indicator bulb, not because of the power dissipation, but because of the high voltage.  A 1/4 Watt resistor will arc and burn.

Protection Circuitry

Resettable fuse: 576-600R150-RAR
Voltage: 350 V maximum
Current 300 mA
https://eu.mouser.com/ProductDetail/Littelfuse/600R150-RAZR?qs=sGAEpiMZZMsgjL4JkW1EEUfdUrimm9NEBXyO2non48E%3D
$1.08

Gas arrestors: From each mains wire to ground
Gas arrestor: 652-2045-40-BT1LF
Spark over: 400 V
https://eu.mouser.com/ProductDetail/Bourns/2045-40-BT1LF?qs=qcv5MX6YzaKx5e3H%2FmTy%2Fg%3D%3D
$0.819

Common mode choke: 10 to 20 turns, double wound
Toroidal core: 80-ESD-R-10E
Size: 10 mm OD, 5 mm ID, 5mm height
https://eu.mouser.com/ProductDetail/KEMET/ESD-R-10E?qs=BenOyfdfAroZzp6LE7YowQ%3D%3D
$0.18

Also put a 1 Megohm 2 Watt bleed resistor in parallel with the capacitor banks.  You won't be sorry if the capacitor is safely discharged when you touch the wires...

Test the HT supply with a 33 kilohm, 5 Watt resistor.


Indicator Lamp
What is a power supply without an indicator lamp?  A little NE2 neon bulb with a 1M to 3M3 resistor in series over the 325 VDC supply output will work, but it will be boring.  If you put a 470 nF or 1 uF capacitor in parallel with the bulb then it will flash - a relaxation oscillator.  

The capacitor will never see a voltage higher than about 90 V, but if the neon would ever pop, then the cap will pop too, so it is best to use a 1000 V ceramic capacitor.  

Please don't use a blue LED with valves.  A blue LED in a valve circuit should be illegal - A crime against humanity.

Personal Safety

When you work with thermionic valves, be sure to put a rubber carpet on the floor and house your project in a well insulated ABS, bakelite or wood enclosure, away from curious little prying fingers!

Power on: Put a piece of transparent plastic over the project and stand some distance away when turning it on.  A capacitor may explode, or something may arc and maybe you can see what happened through the plastic shield and smoke...


La Voila!

Herman

Monday, July 20, 2020

Its Over!

The Covid19 epidemic is over, but people are so scared, because of the exponentially exaggerated projections, that they now refuse to listen to reason, as explained in this video https://www.youtube.com/watch?v=gHbwAd5gkMM

A big problem is that the crazy-news media concentrate on the scary projections and ignore the real statistics.  Let's look at the USA CDC Covid19 death count report Table 1 - literally the cold hard facts


Over the hump

After the very vulnerable people sadly passed away, the illness continues to burn through the healthy population, the majority of whom will not get seriously sick, the death rate keeps going down and is now around 1500 per day, which is very low compared to the peak.

Every week, you can go back and look at a new version of this graph and every week you will see that it doesn't go back up, it just keeps going sideways.  It is a very boring graph and in this case, boring is good.

In the US, even the president is not allowed to point out publically on Twitter that children are almost immune to the disease, as shown clearly in the CDC graph above. The whole thing is terribly politicised there and the Democrat mass media controls the narative, science be damned.

The death rate is independent of the infection rates, so loved by the crazy-news papers.  There are no strong peaks in the table when the infection rates climb, NY stopped their lock down, political rallies broke the lockdowns, etc, meaning that all the preventative measures have had little to no effect on the death rate.


Sweden with no lockdown, had lower slopes than the UK with lockdown.

This disease is extremely contageous, it is in the air, it is carried by pets and other mammals.  It is in our food supply https://news.sky.com/story/coronavirus-outbreak-at-sandwich-factory-as-nearly-300-staff-test-positive-12048597 and the expensive lockdowns were not effective.  It may have prevented some healthy people from being inconvenienced, but it did not prevent old and sick people from getting sick with Covid19 and dying of it.  Deaths are only prevented by medical intervention and treatments in hospital.  

The lockdowns clearly did not 'flatten the curves' - the disease carried on spreading - Sweden's curve is 'flatter' than either Belgium or the UK, while many Central and East European countries have so few deaths, it is in the noise floor (Slovakia with 5 million people, had 30 deaths in total).  The disease is clearly only a problem in South-Western Europe and the Americas - the rest of the world is largely immune to it - probably due to a different immunization regime.

Lockdowns are even worse than not helping, since many people died because of the lockdowns for reasons such as hunger and lack of medical treatment of other conditions:

Graphs for every country in Europe look the same.  The graphs go up steeply and come down slowly, just a few weeks earlier in time, compared to the US.  

In the England and Wales in the UK, the Covid19 death toll decreased for the 20th consecutive week and is below the Infuenza death toll since June 2020




In Europe, Covid19 is fish paper - yesterday's news.


North America is not far behind Europe and indeed,  for the past 3 weeks, deaths from all causes in the USA was also below the expected.  See Table 1, Percent of expected deaths:

These graphs are updated once a week by the CDC.  One cannot argue with this data since it is not predictions, it is real stone cold deaths.  Normally, deaths are dispiriting, but in this case, the contrast is so stark with the wild exponential predictions, that it is actually encouraging and unlike James Bond, people only die once.

Of course, once the death rate bounces back up to normal, the crazy papers will tell of the second coming of Covid, while the near zero bumps in the curves are really because all the vulnerable people died a few weeks/months earlier than they would have without Covid19.

Lately, there is news in Europe about a second wave of infections.  We shall see what happens in two weeks with the death counts, after the Grim Reaper walked by.  My hope is that there won't be many, since this wave is amongst younger people - and guess what, weeks later, the death rate just keeps going down.

More information on real numbers vs scary exponential projections, done by people in the insurance industry, who wanted to know what would happen to their businesses if people really started dying in droves as the projections indicated: https://www.pandata.org.za/

"The death rate is inversely proportional to the amount a country spends on health care."  

This conundrum is due to the disease disproportionately affecting older people (80%).  Poor countries don't have old people - they die young, since they don't invest in health care.  There is also some new research coming in on Covid19 vs age and immune system T-cells (old people have fewer), which may explain the problem and lead to new treatments.
 
Here is a graph that Americans are not allowed to see.  If you are American, please close your eyes and don't peep:


According to the BBC, more than 50% of Mumbai slum dwellers already had Covid19 and the death rate is about 1 in 2000, or 0.05%, which is so close to zero that one cannot graph it - you will only see the x and y axes with nothing in the graph:

Send the children back to school, they will be fine.  The older teachers may have a worry, but not the children.

Why is Boris Johnson wearing a mask?  He already had the illness.  Apparently he forgot.

It's over folks.  Light a candle for the lost souls and move on.  

--oOo--

The Weekly Virus
According to these BBC graphs, the relationship between the scary case numbers and actual deaths, is clearly very weak.  


The main take-away appears to be that if you need to go to the US, schedule your business over a weekend and you will be safe...
 
The testing system clearly doesn't work properly, produces very large numbers of False Positive results and is therefore mostly a waste:
 

--oOo--

Further reading: 
Calling Bullshit
The Art of Scepticism in a Data-Driven World
Jevin D. West (author), Carl T. Bergstrom (author)

--oOo--

Dear lord, please save us from the Crazy Doomers...

--oOo--

Vaccines
Specific vaccines are now in the test phase:

However, an old stalwart, the BCG vaccine, seems to be almost as good (about >80% of deaths are prevented) and it is available right now.  

Luis E. Escobar,  View ORCID ProfileAlvaro Molina-Cruz, and Carolina Barillas-Mury
PNAS July 28, 2020 117 (30) 17720-17726; first published July 9, 2020 https://doi.org/10.1073/pnas.2008410117

So if you don't have the TB vaccine marks on your left shoulder, maybe you should get it: https://www.sciencedaily.com/releases/2020/07/200708121433.htm  

A little googling will find more results, since several BCG tests are now drawing to an end, but the result is obvious to those who care to look at the death rates in Eastern Europe: 30 in Slovakia, 600 in Belarus, meaning that more people die per day in the USA of Covid19, than in six months in these countries.

--oOo--

Stop worrying and get a BCG shot:

Covid19 was only a problem in about ten countries in the world, which doth not a pandemic make.

Type this into Google: "covid deaths slovakia", or any other European country, to get a nice graph.  Note that Slovakia is exactly in the centre of Europe:

That number 6 is really six, not six thousand, or six hundred, just six.  Most of Europe looks similar.


--oOo--


Ignore the crazy unscientific predictors of doom.

Don't make a mountain out of a mole hill.
 
Get all available vaccines.
 
Enjoy life.
 

La voila!

Herman

Sunday, July 19, 2020

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 antenna is much wider than the conventional old one, which is very promissing, but I need to work on my RF cables, connectors and calibration kit, to get proper graphs, since the VNA seems to be out of calibration.

I don't have an anechoic chamber - I hold two antennas in my hands and rotate them 90 and 180 degrees to see what is going on - good enuff!

Performance Graphs

I eventually charged the battery of my VNA (Having decent power sure helps!), reread the manual and reset the calibration (Func Shift 7).  I also verified that there is no significant difference between Sys Cal and User Cal with my cables, so it is good to go.




Bandwidth of 120 MHz at 3.1 GHz

For comparison, here is the previous simpler antenna with 1 mm wide straight elements:


Bandwidth of 30 MHz at 3.38 GHz

A low VSWR is important for a transmit antenna.  Modern day radios have Gallium Arsenide semiconductor drivers that can get damaged very easily by high voltages.  The better radios have self protection circuits that will reduce the output power if there is a mismatch, but El Cheapo radios may simply heat up and melt down.

Vacuum tube radios can handle enormous voltages, so the old clunkers can simply be tuned for maximum smoke, but the missus may not want to have a hot and sizzling 1 meter tall Klystron tube in the living room, although it could be quite a discussion piece.  Travelling Wave Tubes are still used in some K band satellite transmitters, so vacuum tubes are not just ancient relics of microwave ovens!

Summary

Flaring the antenna elements to 3 mm and 10 mm does help significantly to widen the bandwidth of the Yagi antenna by 400% and it still has the nice linear Phase, VSWR and Impedance characteristics of a conventional Yagi, but the antenna is still quite narrow band, compared to a Log-Periodic antenna for example.

The centre frequencies are somewhat different, because the new one is made on FR2 and the old one on FR4, but I also plotted the new one more accurately in KiCAD.  To get a PCB antenna exactly on the frequency you want, will take three to five iterations.  That is just the nature of the game.

I think that the bandwidth can be further widened, by inserting cross pieces to make the elements more like cones.  Maybe I'll try a Conehead antenna another day.


Have Fun!

Herman

Monday, July 13, 2020

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 popcicle 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 way would be to file a ring in the end of the bolt, cut a washer in two and glue that into the block, but that is a lot of hassle - another day - do, do that on a big clamp.


It it really worth making a bar clamp?  Of course not!  One can buy a perfect clamp for a few Dollars, but what is the fun in that and what else can you do with a bag of craft store pop sticks?


Have fun!

Herman