A Tale of Two Tubes

A couple of weeks ago, I worked N4QR on 40m CW. I could tell by the tone of his signal that he was operating a homebrew transmitter. There wasn’t any 60 Hz on his signal, and it didn’t chirp exactly, but I could tell it wasn’t the pure tone you get out of today’s radios.

I asked him about his rig, and he told me that it was a one-tube transmitter made with a 6L6. I forgot to ask him where he got the schematic, but a quick Internet search turned up the following:

  • The May 2005 issue of the K9YA Telegraph has an article written by N4QR titled, “The Wonderful One-Tuber,” that contains the schematic for the transmitter. The K9YA folks don’t make issues of The Telegraph available on their website, but I was able to get a copy of the issue by e-mailing them.
  • A 6L6 Classic (shown below)
  • WB2MIC 6L6 Transmitter Project

This one-tube transmitter is made with a 6L6 pentode.

The 6L6 is a pentode that, according to Wikipedia, was introduced by the Radio Corporation of America (RCA) in July 1936. Apparently, it was used quite a bit in public address systems.

After the tube became successful, tube manufacturers introduced a number of variations, including the venerable 807. The original 6L6 was capable of delivering 19 W; the latest variation, the 6L6GC is rated for 30 W. The 6L6GC is still used in guitar amps, and is still manufactured in Russia, China, and by Groove Tubes in the U.S. They sell a number of different 6L6 variants; the cheapest is $16, the most expensive $180!!

Tube #2
One of the reasons I was interested in the 6L6 is because about a year ago I came across a schematic for a transmitter using 6A6 dual triode. I had just come into possession of a couple hundred tubes, and while I didn’t have a 6A6 (at least I haven’t found one yet), I do have a couple of 6J6 dual triodes. They’re not quite as high power as the 6A6, but I’m still thinking about building a little transmitter with one.

As you might expect, there’s a bunch of information on the Internet about this tube:

One interesting fact about the 6J6 is that IBM used it in the 604 computer. Unfortunately, they found it to be not as reliable as they wanted it to be, but at first none of the tube manufacturers were interested in making a more robust version. This led IBM to set up a tube-making laboratory where they could experiment with designs. They developed a more reliable version of the 6J6 and finally convinced RCA to manufacture the tube. According to the author of the history of the 604, part of the concern is that IBM would decide to get into the tube business.

So, the next time you hear a signal that doesn’t sound so perfect, remember that there just might be a story behind it. Ask the op about his transmitter, and listen to what he or she has to say.

Showcase Your Construction Projects

From Terry, WA0ITP, via the qrp-.org mailing list:

Do you need an enclosure slightly larger than an Altoids tin? Would you like to see your project after building it, instead of hiding it? If so, this enclosure is for you! This is an Altoids tin on steroids. Check it out here.

One of these nifty enclosures is used to house the demo model of our very successful Enhanced Manhattan Islander Audio Amp. It shows off the K8IQY design and K3PEG’s EM Template nicely.

Introduced at OzarkCon 2009 in Branson to gage the acceptance of the clear top, our entire stock sold out! It’s obvious that this enclosure fills a niche in enclosure size and style, so we’ve added to our product line.

The dimensions are: 5.5″W x 3.7″L x .9″H, making it ideal for the many projects that are just a little too large for an Altoids® or Whitmans® Tin. The top is hinged just like the Altoids, and it is a food grade container.

Please place your order soon as these will sell quickly.
I love this radio stuff !
72, 73 Terry, WAØITP

I just ordered three for myself…….Dan

Yet More Links

Here are more websites that I’ve come across that could be of interest to amateur radio operators:

  • MIT Open Courseware. Want to get an MIT education without moving to Cambridge or paying high tuition? Take courses online! Of course you won’t get an MIT degree, but I bet you learn a lot. One place you might start is 6.071 Introduction to Electronics.
  • W5LET’s Bare-Essentials Transmitter. 1968 was a simpler time. That’s the year this one-tube transmitter project was published in Electronics Illustrated. It’s articles like these that got me interested in ham radio. Find a 50C5 and build this rig.
  • W5GI’s Mystery Antenna. I found this antenna while looking for a design for an 80m antenna that would fit on my lot. I haven’t built this antenna yet, but it’s on my list of things to do.
  • Amateur Radio Special Events. I like working special events stations, both operating them and contacting them. Here’s a website devoted entirely to special event stations. For example, it lists the following taking place in November:
    • XE2BC – Nov 10 – XE2BC , founded in 1946, will celebrate the founding date on November 10th 2006
    • K6PV – Nov 12 -15 – mini IOTA DXpedition to Santa Catalina Island (NA-066) California
    • ARMAD – Nov 13 – Amateur Radio Golden Corral Military Appreciation Day
    • W6OI – Nov 25- 26 – 10 -10 International Club Station Special Event
  • Ridge Equipment Company. This company sells both new and used test equipment, including dummy loads and attenuators. The prices for the used gear looks pretty good.