"One Linear Transmitter"

Use of these circuits is subject to the laws of your country of residence.
This information is provided for educational purposes and/or authorized usage only.

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

http://electronbunker.ca/eb/OneTubeXMTR_2.html

To see this same TX with a - Tuning Eye - click here!

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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.

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 'newby' to this site and you are thinking about building your first transmitter from a print found here, I'd recommend you build this one. It's easier to build than some. It only has 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 impressive, just as Bob mentions on his site.

http://electronbunker.ca/eb/AM_StereoXMTR.html

How does the 'Goldberg' transmitter compare to this TX? Well, the Goldberg modulates better but is not quite as linear. Keeping a vacuum tube linear seems to limit it's output level, thus the lower modulation. However, I cannot say that I hear a sound quality difference otherwise. At least enough to say that one is better than the other, so both are enjoyable to listen to.

Modifications:

  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".

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Click on the image below for a larger schematic.

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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!

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To answer your FAQ's

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1942 Philco Radio - Model 42PT-7