The Two Tuber 8 watt Transmitter

The Two Tube Transmitter - QST January 2003

Hello all.  In 2003, after reading this interesting article in QST, I decided that I too have to build this tube transmitter.  The article by Steve Johnston, WB8DAS, was actually built in a tuna fish can.  I decided that the tuna can idea would not really work for me.  So now fast forward to 2018.  Finally after 15 years, I got started by building the power supply onto a wooden board.  Fortunately, I had purchased all of the parts, or almost all of the parts back in 2003 or 2004.

The Two Tuber under construction with the power supply in place

In the above photo you can see the power supply is secured to the board.  The front panel is a piece of sheet steel with TX/RX, On/Off, Fuse, On-light, TX light, key jack;  I might add other things if I can think of any.  The rear panel which is not yet installed will have a jack for the antenna, and oh yes, the front panel will also have a socket for a fundamental crystal.

The most difficult part of building this transmitter will be your power source for 6.3vac and 250vdc.  The filament voltage on the tubes is 6.3vac.  If  you have a way of putting together the power supply without using the Radio Shack transformers pictured above, then you are in good shape.  I have no clue at this time if you can find these transformers.  There are other power sources, but I recommend reading the article from QST to review the power supply.  Everything else is obtainable without too much trouble, probably even the tubes.  The tubes are V1...6C4, and V2...5763.

Once you have obtained the parts, then the next biggest hurdle is to wind inductor L1.  L1 is 32 turns of #20 wire 1 inch in diameter and 2 inches long.  It sounds simple, but the article says to use a B & W type 3015 miniductor.  This inductor is not cheap, and so not being so eager to spend a lot of money on one part, so I decided to roll my own.  

Homebrew Mini Inductor

There is an excellent article on homebrewing your own inductors.  Here is the link:

http://www.arrl.org/files/file/Technology/tis/info/pdf/9708033.pdf

The truth is that making your own inductor like the one I made in the picture above is difficult.  You must make sure that the coil is spaced so that nothing touches.  The epoxy has to do the job also and you must make sure that the epoxy penetrates enough to hold the AWG 20 wire in place.

So far the project has been educational and slightly challenging for someone who always thinks "Solid State."  For the old timers, this project may be reminiscent of transmitters they built as a novice.

At a minimum, I certainly advise you to look up the old QST article just for the fun of reading through the project steps.  It is also important to keep in mind that if you decide to build this tube transmitter, then you must play it safe and remember that you are dealing with AC voltages.  The author reminds us in the article that the key is hot also.

Have any questions or comments?  Please feel free to post.  I will be putting up pics of the homebrew circuit board that I am going to prepare for this project.  It will be absolutely non-fancy, but will hopefully do the job.

73 for now, Mark 4x1ks