Electronical Excitement

(#0180) Spectacular Failure and Replacement of Vacuum Tube in Atwater Kent 55C AM Radio
[Action starts at 4:50 and runs to failure at 8:00]
Roberta is taking out about out an old radio transmitter and she mentions that Kennetron repairs vacuum tubes, so I go looking for pictures and I find this video. This guy isn't actually repairing a vacuum tube, he's jury-rigging an adapter in order to make use of a different tube. Now he has a bad tube which he proceeds to run to destruction for our amusement (above). Kennetron only repairs vacuum tubes which are worth repairing, i.e. big industrial / commercial tubes. They aren't going to repair the tubes in your audio amplifier.

Tektronix R7912

Tektronix Logo

At lunch today Jack regaled us with a tale about a state-of-art instrument he worked on during his tenure at Tektronix. The machine used a convoluted method to measure very short transient signals, that is signals that only appear occasionally, and only for a brief period of time.

Tektronix R7912 CRT

The machine used a CRT from an oscilloscope and a primitive digital camera to record very fast transient signals. The CRT was buried inside the machine, it was not visible to the operator. The signal from the probe was used to draw the pulse on the screen of the CRT. The digital camera faced the CRT and digitized the projected image. This was back in the early 1970's, and the digital camera had a very low resolution, about one-quarter of a mega-pixel, to use today's parlance.

Preparation for an underground nuclear test at the Nevada Test Site in the 1990s

The big customer were the guys doing underground nuclear bomb tests. They would bury a bunch of these instruments in the ground along with the bomb. When the bomb was detonated, the R7912 digitizers would send out digital information until the detonation destroyed them.

Tektronix R7912 Front Panel

This gadget is so weird I thought I better include another description of it. From Tekwiki:

The Tektronix 7912 is a series of high-speed digitizers that take one 7000-series vertical plug-in and one 7000-series horizontal plug-in.

All 7912 models use the same internal CRT-based, digitizing scan converter tube (T7912) that is not visible from the outside. The signal from the vertical plug-in deflects a writing beam through distributed deflection plates. The electrons hit a small flat rectangular solid state target, conceptually similar to the image sensor in a digital camera. The resolution of the target is 512×512, giving 512 points in the time domain and 9-bit linear quantization of the input voltage.
With a 7B92 sweeping the whole X-axis in 5 ns, and the 7912 capturing 512 samples in that sweep, the 7912 performs the function of a 100 GSample/s A/D converter.

5 nanoseconds divided by 512 samples, means we are taking 100 measurements every nanosecond, which means our sample rate is 100 billion measurements every second, i.e. 100 GSamples/s.

The Biggest Aspidistra In The World

Gracie Fields The Biggest Aspidistra In The World 1938
Marcel got me started with this quote from Fake News by Richard Fernandez on PJ Media:

The reason why Allied deception operations were so effective against Hitler was because Goebbels had reduced German reporting to a lie machine, thereby destroying its credibility. Allied news, even Allied deception was more believable by comparison.

Cool, we're talking about veracity here, always an interesting topic. I want to read more. Starting from the top, Richard talks about the transmitter the Brits were using to pump propaganda across the channel:

It was not long before the British were running their own fake news operation against Nazi Germany under the 20 Committee. In this they were materially aided by the power of American technology. Rowen notes "If you ever listen to radio these days, you’ve probably heard “50,000 watts clear channel”. Today, as in the 1940s, it is still the maximum power allowed a US radio station. But in 1941, the RCA Corporation in New Jersey built for WJZ a transmitter 10 times more powerful. When the Federal Communication Commission refused to lift its ceiling of 50,000 watts, the WJZ 500,000 watt transmitter was briefly orphaned. Until the British heard about it. The transmitter was crated up, shipped to the UK and installed in bombproof headquarters in Sussex. They named it after a song sung by the English music hall entertainer, Gracie Fields: The Biggest Aspidistra in the World!"

That's how we got the video at the top. Gracie was a big deal back in the 1930s.

Now I go looking for information about the transmitter, and I'm not really finding much.

Water Cooled Vacuum Tubes for the Aspidistra transmitter

But then I stumble over the Alexanderson alternator: 50 tons of steampunk radio transmitter. This might be what prompted Gracie to sing her song.

Alexnderson Alternator

 An Alexanderson alternator is a rotating machine invented by Ernst Alexanderson in 1904 for the generation of high-frequency alternating current for use as a radio transmitter. It was one of the first devices capable of generating the continuous radio waves needed for transmission of amplitude modulation (sound) by radio. It was used from about 1910 in a few "superpower" longwave radiotelegraphy stations to transmit transoceanic message traffic by Morse code to similar stations all over the world. Although obsolete by the early 1920s due to the development of vacuum-tube transmitters, the Alexanderson alternator continued to be used until World War 2. It is on the list of IEEE Milestones as a key achievement in electrical engineering. - Wikipedia

Alexanderson Alternator Rotor

The rotor is five feet in diameter and turns at 2100 RPM.

Alexanderson Alternator Rotor

There is still one machine is Sweden. They fire it up a couple of times a year just so they can prove that it still works.

Merry Christmas in Morse Code
You can see the code just above the letters.

Update July 2021 replaced missing video.

Vacuum

Evangelista Torricelli

I started watching Geissler Tubes - Periodic Table of Videos, but the professor is not the most engaging speaker. The subject is intriguing, so I go rooting around and find a all kinds of interesting stuff.

• Chemistry World has good story about the whole three century ordeal, but their website seems to be a little flakey. Fortunately, I made a copy of the story and you can read it here.
• Heinrich Geißler (1814 – 1879), famous for his invention of the Geissler tube.
• Julius Plücker (1801 – 1868), pioneer in the investigations of cathode rays that led eventually to the discovery of the electron. He asked Heinrich to make him a vacuum pump. 
• Hermann Sprengel FRS (1834 – 1906), chemist, who also happened to invent the mercurial air pump, a big improvement over Heinrich's pump.
• The Cathode Ray Tube site has a page about Geissler Tubes.
• Previous related post.

Sov-Tech

Thank god for the Russians. What we previously thought was a bad vacuum tube turned out to be nothing more than a broken wire in the speaker jack. Soldering that back together put the Marshall JCM 900 back in operation, until it broke again about a week later. This time I noticed a purple glow in the back, and I thought, hey, that's kind of cool. It's not too obvious in this picture, at least compared to the one glowing the bright cherry red.

Taking off the back made it more obvious. A little research tells us that the purple glow is ionized air that has leaked into our vacuum, so it looks like we are going to need a set of power amplifier tubes after all.

Here's our set of new tubes from Old Town Music. Made by Svetlana. In Russia. Who'd a thunk we'd be buying electronics from the commies for an amplifier made in socialist Britain?

Microphonic

My son wants to get a tube type amplifier for his stereo. He sent me a link to Maker Shed and Tube Depot, two companies that offer reasonably priced kits. The Tube Depot also offers vacuum tube carrying cases, and they are described:

For maximum performance and longevity, vacuum tubes should always be stored and transported in a safe and secure fashion. The TubeCube and the TubeCube Pro provide a customizable shock-resistant environment for your tubes and helps prevent them from becoming microphonic or damaged.

Okay, "damaged" I understand, but microphonic? What the heck is that? From Wikipedia:

Microphonics describes the phenomenon where certain components in electronic devices transform mechanical vibrations (ringing) into an undesired electrical signal (noise). The term is derived by analogy to older microphones where that behavior is inherent in the design, while with modern electronics it is sometimes an intentionally added effect.
When electronic equipment was built using vacuum tubes, microphonics used to be a very serious design problem. The charged elements in the vacuum tubes would vibrate and the motion would change the distance between the elements, producing charge flows in and out of the tube in a manner identical to a capacitor microphone. A system sufficiently susceptible to microphonics could experience feedback.

Sometimes this technical stuff just comes out of left field and whacks you upside the head. It's perfectly obvious now how vibration could cause problems for vacuum tubes, but it's something I never heard of before. Weird.

My son isn't the only one with the vacuum tube bug. Witness this new car radio, now with a vacuum tube. Update: it's not new, it dates from at least 2005.

And no discussion of vacuum tubes is complete without this video from Claude Paillard:

Fabrication d'une lampe triode
by F2FO

Update January 2017 replaced missing image.

Home Made Vacuum Tubes

Cool video of a guy making his own vacuum tubes for a radio. It's on some video service I don't recognize, so I am having to give you the link to the web pages that have the video. I haven't figured out how to post it directly.

You can find it at the bottom of this page:

http://paillard.claude.free.fr/

Update December 2016 removed dead link.