Posts Tagged ‘breadboard’

More on 6V6 and 6L6 Vacuum Tubes in Transmitters

January 26, 2015

We previously discussed how vacuum tubes are used differently in code (CW) circuits than in audio circuits. In simple code circuits, such as the Pastime Projects “Remember When” reproduction “breadboard” transmitter kit, or the new 6V6 MC  kit, the tube can be thought of as a switching amplifier/oscillator. The tube is biased and set so that it either operates at optimum capability or it is silent (off). On or off.  It’s that simple.

In a crystal controlled oscillator circuit, there are many other factors.  We quickly learn that crystals vary in activity, current carrying capabilities, stability, temperature drift and other factors.  In putting the cw tube type transmitter on the air, we are concerned in transmitter the best stable and chirp free signal we can.  The best signal may not occur at the peak output point, and it is important to sacrifice a bit of output for best signal.  Maximum power out with best possible signal quality is our goal.

While it may not be so obvious today, the “RST” code (Readability-Strength-tone) was derived to grade a signal on its quality at a distance station. The “T” portion of this report dealt with tone.  While this is not a consideration much today, back in the days of crystal control, especially in the novice days after World War Two, the tone gave us a good idea of how bad (or good) our surplus crystals were working in our homebrew transmitters.

We have been testing each of our tubes in a transmitter circuit before stocking for our kits. The 6L6 tubes are a heavier duty tube than the 6V6 tubes. We have found either work very well in our transmitters, with the 6L6 giving a little more output than the 6V6 with the same power voltages.  (The current draw is a little heavier with the 6L6, but our power supply can handle the difference with ease.)

Please consider our 6V6/6L6 tubes next time you are in the market.  Of course, one will be included in your new Pastime Projects 6V6 type transmitter kit.

We have a few new “Coke-bottle” style 6L6 tubes (which are no longer available) left in stock. They are great performers and they add to the vintage look of our “Remember When”  6V6 Slat Board transmitters.  Contact us for more information.

http://www.pastimeprojects.com or  pastimeprojects (at)yahoo(dot)com.   73  Glenn W8JZI