Thursday, May 2, 2013

Vacuum Tubes, a "Modern Aladdin's Lamp" by AT&T

Some of the early glass tubes used in transmitters were truly works of the glassblower's art.

When I worked at Fermilab, the RF Power Amplifiers used in the Booster and Main Accelerators used water-cooled metal-ceramic tubes made by Eimac.

They were 4CW100000X, indicating they had a Plate Dissipation of 100,000 Watts!

A quick look at the "Eimac" website doesn't show them listed anymore, so I'll have to get a hold of my buddy Dave who still works there and find out what they're using these days.

Anyway....a friend of mine sent me the link to this AT&T video about the Good Old Days.



  1. I know that this is not what you were trying to get at, but I always thought that there was a sense of beauty in the old vacuum tubes. They simply looked cool. Touching them, replacing them, and working with them had that interesting plug and play aspect that spoke to the tinkerer in all of us.

  2. I just sold a vacuum tube voltmeter. Fun stuff!

  3. I've always thought that kids growing up since the advent of solid-state electronic components have missed out on something truly amazing. Thanks.

  4. Yep, tubes are definitely neat.

    As I was growing up and getting interested in electronics, I learned a lot about tubes. Most Amateur Radio gear was tube based at the time, with solid-state devices coming on to the scene in the late 70's.

    Then I learned about solid-state, and when FET's started to get popular I was in a good position to explain the difference between voltage controlled devices (tubes, FET's) and current controlled devices (bipolar transistors). Some people just couldn't understand the fundamental differences between the way they operated, and I saw lots of design errors made.

    Long Live Hollow-State!

  5. Ha! Hollow-State indeed. I have a Nixie tube clock that freaks people out.

  6. When I started engineering school they were teaching vacuum tubes. There was one introductory solid state course at the senior level. By the time I graduated the transition was well underway even teaching some integrated circuit courses. Good thing it took me 7 years part time.
    The IBM 7090 was shared with the National Hurricane Center.

  7. Remember when every hardware store had a tube tester where you could see if your tubes were still good?

  8. And most drug stores had them, too.

    One of my cousins ran "The Best Damn TV Shop in Joliet" (apologies to Smokey Yunick), and he would always tell me stories of people who had pulled their tubes out to be tested, and then not get them back in the correct sockets, or force them in the socket without the pins being properly aligned.

    He said those calls were always good for several tubes if the customer was lucky, and sometimes much more if the wrong tube in the wrong socket took out some other components.

    He loved those tube testers on every corner!

  9. The old Super Connie had a 13KV Maggie in it, basically one BIG tube!!! Great video, thanks!

  10. One big tube with one BIG magnet!

    I lost track of the number of times the Techs at DirecTV would get the mag stripe on their badges wiped out when they were working on the klystrons in the high-power amplifiers.

  11. I'm not ashamed to say I actually got goosebumps in parts of that. What an amazing video.

    My first electronic "adventures" were with vacuum tubes. I remember breaking one open to see the inside parts better. And I remember the disappointment of the first transistor I tried that with, in a tiny metal can. I still have a couple of good, hollow state radios: an R-390A and a KWM-2 (not the A version). The KWM-2 is an excellent HF ham station, but I hardly use it. My modern radios run rings around it in terms of features and operating conveniences (read "bells and whistles"). But it's not going anywhere; I'll keep it going until I can't keep going. The project engineer who led the KWM-2's design team was a friend's next door neighbor and I got to chat with him several times.

  12. Yep, I did the same thing when I was just learning.

    I also learned that a VR tube will light up *REALLY* bright if you connect it to a stiff power supply without a current limiting resistor.

    My Flex 5000 will run rings around my Hallicrafters SX-117, and my Drake R4-B, and my Kenwood TS-950SDX with an Inrad roofing filter and a full load of Inrad IF filters, BUT....I can listen to the R4-B for hours without fatigue.

    It's just got that "something" that a well-designed receiver has that makes it very pleasant to listen to.

    1. I have a theory of why my KWM-2 and your R4-B are easier to listen to. Modern rigs are designed to AGC on noise, so that the total audio power delivered to the speaker is the same no matter what you're listening to. The older radios let the RF get a little higher before they AGC, maybe 10 or 20 dB SNR, so that the noise is lower. Add that to (in general) better audio design and they just sound better. My home station uses an external "hi-fi" speaker that just sounds better than the little one inside the case.

  13. I'm not sure how the AGC affects the sound of the audio in the way that gives me fatigue. I'd think it's more in the actual audio circuitry. I know a Drake R4-C sounds really bad when they're "stock", due to a number of design compromises. There's numerous articles around about how to modify the C model to fix the crappy audio. My R4-B sounds pretty good "as-is".

    The Hallicrafters SX-117 audio is "kinda OK" out of the box, but there are a few mods you can do to greatly improve it, like changing a couple of capacitors. The audio output tube is a 6GW8, commonly used in portable phonographs of the time, and will distort REALLY bad if it's the slightest bit gassy.

    The SX-117 skimped on the power supply design, and has a bit more ripple than it should. Bigger caps don't help, as it really needs a choke-input filter.

    I've never used a KWM-2, but I have a 75S-1 I've been working on for a while now. One of these days I might even finish it!


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