PDA

View Full Version : Ever Hear of Barkhausen Oscillation ???



NM5TF
07-22-2014, 11:24 AM
and no, it's NOT that noise your Dog makes at 0300 when he wants to go out to take care of business....

it's this...

"Barkhausen Oscillation
There is an unusual and little-known way to make triode vacuum tubes oscillate at frequencies far above where they normally can be used. The method involves operating the control grid at a moderately high positive voltage with respect to the cathode and the plate at a zero or negative voltage with respect to the cathode. Under these conditions the grid attracts electrons from the cloud of electrons emitted by the hot cathode. Those electrons are accelerated to high velocity by the relatively high positive charge on the grid. Some electrons hit grid wires, but most miss the grid and fly on through toward the plate. However, the plate is negative with respect to the grid, causing most of the electrons to reverse direction and head back toward the grid at high velocity. Some returning electrons hit the grid, but most fly on through toward the cathode. However, the cathode is negative, so most of them reverse again and continue oscillating about the grid. This oscillation mode is known by the few who know about it as Barkhausen Oscillation (different than Barkhausen oscillation criteria)."

K6BSO
07-22-2014, 11:48 AM
Paraphrased from the Wikipedia:


The Barkhausen-Kurz oscillator, invented by Heinrich Georg Barkhausen and Karl Kurz, was the first oscillator that could produce radio power in the ultra-high frequency (UHF) portion of the radio spectrum, above 300 MHz. It was also the first oscillator to exploit electron transit time effects, and inspired research that led to other transit time tubes such as the klystron. It was used as a source of high frequency radio waves in research laboratories, and in a few UHF radio transmitters through World War ll, but was superseded by other tubes like the klystron.

Interesting article (if you're a nerd) here (http://en.wikipedia.org/wiki/Barkhausen-Kurz_tube).

WX7P
07-22-2014, 12:12 PM
Barkhausen by proxy, anyone?

K7SGJ
07-22-2014, 12:26 PM
Thanks for posting that.

When I worked in a TV repair shop (TV was in it's infancy) any time we had a strange problem no one had seen before, the diagnosis was always Barkhausen Oscillation. It was a great catchall for "beats the shit out of me".

One of us finally had enough curiosity to actually research it to find out what it was, and enlighten the others. It turned out to be one of those obscure things you never forget, no matter how hard you try. For me, it does bring back some great memories of some really fine people, though. And a lot of trips uphill in the snow both ways, too.

K6BSO
07-22-2014, 01:02 PM
Barkhausen by proxy, anyone?

How about Barky Barkihausen, the master of stop-motion animation film making?

XE1/N5AL
07-22-2014, 01:45 PM
Another thread about keeping those plates at ground potential? :)

Interesting subject. If I still had some vacuum tube stuff to play with, I'd give it a try -- just to see if I could get a junkbox triode to oscillate. If you used a tetrode tube, I wonder if you could key the screen grid, to control the oscillation, and send Morse code? Though, with oscillation start delays, it would probably sound awful.

12744

kb2vxa
07-22-2014, 03:10 PM
"...any time we had a strange problem no one had seen before, the diagnosis was always Barkhausen Oscillation."

In our shop it was snivets. My cat's name was Sam, Sam Katz. He was snipped so he must have been Jewish. If he was a dog his name would have been Snivets Barkhausen but I digress. Now to something serious, (Who, ME serious?) in my basement shop at home I was testing tubes one day in my ancient Precision Apparatus 654 emission tester when a 6BG6 produced a herringbone pattern on channel 2, the only 6BG6 that did it. Just for giggles I stuck the pin in the PL-259 on the coax going to my CB vertical dipole on the plate cap and the shield clipped to the tester's metal panel, pushed the test button and the screen went nuts with a loud hum from the speaker. I cranked the plate voltage as high as it could go and the screen blacked out entirely! I found a weapon for future reference I could use the next time a certain pesky neighbor knocked on the door... MUAHAHAHAHAAAaaaaaa!

Oh, for what it's worthless, the same tube in my B&K transconductance tester gave a null response, it only oscillated in the Paco.