Sunday, October 15, 2017

What Did You Get at the Hamfest, SiG?

Funny you should ask.  I bought only one thing, a book on vacuum tube circuit design.
The author himself was there at the hamfest, selling copies for $20, considerably less than what Amazon is asking. 

Why?  First, a story. 

When I first got interested in electronics as a hobby, vacuum tubes were the mainstay of everyday electronics.  I started out testing tubes at the local drugstore to see if it would fix the family TV, as have tens of thousands of others in my generation.  Transistor radios were common, but so were millions of vacuum tube radios - some version or other of the All American Five - that took 20 seconds to warm up and start playing.  I've worked on vacuum tube circuits, troubleshot and fixed tube radios as a hobbyist.  I still have a couple of vacuum tube radios in the ham shack.  They haven't been turned on in a while.

By the time I started working in engineering, vacuum tubes were used only in a few applications where there was no alternative - mostly high power transmitters.  I started out designing in a mix of discrete transistors with a few integrated circuits and over the years, design shifted as semiconductor makers continued to put more and better integrated functions into a single package.  We could replace complex multi-transistor circuits with a single integrated circuit, often in the same area as one of the transistors we replaced.  This did good things for both manufacturers and our customers: more circuit sophistication brought better performance and getting that sophistication with fewer parts brought more reliability and lower prices.  I'm not quite sure when I last designed a discrete transistor circuit into something, but it was probably over 15 years ago.  After that, the only reason to design in one or two transistors would have been to band-aid a circuit already in production or to design a piece of custom test equipment. 

So why the book?  Now that retirement brings some more time (Hah!) I want to look into some aspects of vacuum tube design.  The audio market for vacuum tubes is alive, vibrant, and getting big premiums over transistor amplifiers.  I have no desire to pay those premiums but would like to hear one side by side with the solid state amp I use.  Perhaps designing and building a vacuum tube-based guitar amplifier would be right up my alley. 


  1. If you haven't watched him before, check out Mr Carlson's Lab on youtube.

    Lot's of glowing glass goodness there.....


    1. Cool channel, so thanks! Haven't run into that guy before.

  2. Vacuum tube circuits are EMP resilient. Now this isn't a cover story for vacuum tube experimentation is it? Hah! indyjonesouthere

  3. Having also made many trips to the drugstore/hardware store to test and replace vacuum tubes as necessary, I remember when transistor radios were not common at all. I remember buying a very small and cheap GE transistor radio when they first became available (in my price range, anyway). The little internal antenna (ferrite core, IIRC?) made for poor reception, so I got up on our roof with a couple of HO gauge train trestles and strung copper wire (I think from a small transformer I disassembled) back and forth and then down to the window into my bedroom. I attached that to the internal antenna, and got much better reception, even though I didn't have a clue about the proper length of wire, orientation, etc. (I did _not_ develop that into an interest in Ham radio, circuit design, etc.)

    Are current vacuum tubes built better than the ones we used in our old cathode ray TVs and radios (like our old Grundig shortwave radio), and are they now expensive, due to improved construction and relative scarcity?

    1. Are current vacuum tubes built better than the ones we used in our old cathode ray TVs and radios (like our old Grundig shortwave radio), and are they now expensive, due to improved construction and relative scarcity?

      In general, tube production shifted overseas to former Soviet bloc countries who never really stopped making them, and China. I've seen Svetlana mentioned as a good brand. The little production still done in the US is specialty tubes, like high-power transmitter tubes. There are some that are very popular in the audiophile world and they run a bit more expensive, but every hamfest has a guy with hundreds of "New, Old Stock" tubes, often still in their Sylvania (or whoever) boxes. Considering the usual comparison to the 1964 silver coins, they're probably cheaper compared to their 60's price.

      As for better built, I haven't read that. If they're making replacements for an existing radio, make them like the old tube.

      Taking the transformer apart and putting the wire on your roof was ingenious. Correct about the ferrite core, btw.

  4. Yep, also remembering the tube tester at the local drugstore, and seeing all the glowing lights when you looked through the cooling slots of the TV.

  5. Many years ago I was a computer repairman for the Air Forces air defense computer system ANFSQ-7. It had about 60,000 vacuum tubes. One of those circuits had a vacuum tube that really had to be new or working like a new tube to pass the tests. So we rejected and replaced a lot of these tubes. But they were still good. So we would repackage them and send them to the radar sites where they also used these same tubes in their circuits. The tubes were good they just couldn't pass the rigorous test that was designed to predict future/eminent failure.

    Another test we would sometimes use was to shut out the lights and look at the frames and plugable units each holding up to six tubes and see if the filaments were glowing. Our tests and techniques were more than adequate to catch/identify most problems right down to the specific circuit but some circuits were somewhat difficult to pinpoint when they failed. So shut off the lights and walk the aisles looking for a tube that's out.

    1. Cool story.

      One of the things the author of this book says is that the military bought tons of tubes for backups for things like that. Those tubes are in the surplus market now.

  6. Another one of your "10s of thousands" ...
    I still have 1960 copies of RCA and GE tube manuals and a couple of textbooks from the pre-transistor era. My wife tells me I have enough vacuum tube equipment (including a 1926 or so radio requiring >real< A and B batteries - but I'm still missing a Magic Eye radio.

    Just in case you're not aware, all Popular Electronics from 1954 on are available at: