Boosted Pierce

Posted on Feb 5, 2014

a Pierce `aperiodic` oscillator driving a non-neutralized power amplifier for a multiband Morse code transmitter that requires just one coil and minimum adjustment. And then one day you happen to unplug the oscillator tube only to find that it still works! This page explores that topology, the Boosted Pierc

Boosted Pierce
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e (Figure 1), from its Great Depression beginnings through its canonization as a ubiquitous "glowbug" design that just won`t go away. Fundamental to understanding the circuit is that it`s an aperiodic-anode tri-tet oscillator that uses separate triode and screen-grid (tetrode or pentode) tubes. Figure 1 ” Boosted Pierce transmitter based on the version described by Don Mix, W1TS, in October 1968 CE QST. Some variations use more or less voltage, regulated or not, on the oscillator; some variations include a cathode bias resistor in the final amplifier and some don`t; some key both stages and some key only the final amplifier; this version uses a voltage divider to supply final screen voltage rather than the series resistor used in many versions. All have the same aim: better performance than an oscillator-only transmitter without the fuss and bother of neutralization ”but it turns out that neutralization is well worthwhile for multiple reasons. Test point T allows measurement of the final grid current, with every 0. 1 V across the associated 100-ohm resistor equating to 1 mA of grid current in the 5763 ”a value worth measuring, because underdrive is likely at 7 MHz and higher frequencies in every Boosted Pierce design that does not overstress its crystal. RS1 and RS2 are proportioned to set the screen voltage to 204 V, key down, in my test version. (Schematic symbols [Tubepad] and original Mix "Novice Special" Boosted Pierce...

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