The "Linear Power TX"

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This TX is a modified version of
"The Improved 1-Tube AM Transmitter"
from Bob’s Electron Bunker


Evan's comments on the original design

First - Bob's one tube transmitter is one of the finest I've come across. It's a controlled carrier transmitter which helps prevent over-modulation and under-modulation. It's amazingly linear and now, with the addition of the RF output stage shown below, it's powerful enough to hear throughout your house using a simple wire antenna.

After building and working with transmitters using a pentode as the oscillator, I can say that this TX is unmatched in its simplicity and performance.

Keeping a tube type TX linear is the challenge and of course the more linear the more true to the original the broadcast will be. Bob's done something special here.

Now, if you are a visitor to this site and you are thinking about building a transmitter from a print found here, I'd recommend you build this one. It's easier to build, with only two vacuum tubes (I chose to use a 1mhz glass crystal from the Ukraine so it looks like 3 tubes) and yet the quality of the audio is truly amazing, just as Bob mentions on his site.

Bob also offers a 3-Tube AM Stereo Transmitter project, maybe that will be the next one I attempt to build?? A bit more challenging. But we shall consider that in the future.

How does the 'Goldberg' transmitter compare to this TX? Well, I must say I enjoy listening to both. There is a slight difference, and both are fantastic. But if I was to describe it, I guess I would say:

1. The Goldberg is a beautiful, sonically rich transmitter. Warm and mello, yet linearly accurate.
2. This 'Power' transmitter has a 'crisp' beautiful sound as well. It is, slightly, more linear than the Goldberg.


  1. Changed Bob's 6CQ8 tube to a 6GH8A. The 6GH8A triode section has a slightly higher amplification factor (46 vs 40) which modulates just a bit better.
  2. Added an RF output section for an increase in the power output. I suggest keeping it to a simple wire antenna. (A wet noodle.)
  3. The power transformer used is the Hammond 262F6.
  4. Cabinet size is 5" X 7".


Click on the image below for a larger schematic.


The schematic above always show the latest updates. Click on it for a full view.

The pictures below may not show every update.

Click on any image below for a larger picture.

The ribbon cable you see goes to the LED's installed in the tube sockets.

All on a single 5" X 7" top!



To answer your FAQ's



1942 Philco Radio - Model 42PT-7