Homebrew 6V6 CW Oscillator

This is my home brew 6V6 rig. The first version was built by my son, N2PNA, over Thanksgiving weekend from a 1944 handbook, when he was 11 and first got his general class. Since then, I have been improving on the original edition. Using a 6L6 at this voltage does not increase output in a meaningful way. The 6V6 does about 6 watts output. The unique power supply design makes for chirp free operation on 80 and 40. The schematics of the trick show a dual power supply, the so called "economy" style used for tube rigs, just before solid state became popular. The primary cause of chirp in these simple rigs is the screen voltage supply. Most designs obtain the screen voltage from the +HV through a dropping resistor, resulting in terrible regulation. Some people resort to a VR tube to correct this problem. The low voltage output is used for the screen supply, so that a high value resistor does not contribute to rapidly changing voltage at key-down. The design shown is sufficiently stable that a VR tube will not improve it measurably. I plan to give this a try on 30 meters with a 6AG7 instead of a 6V6 later, and believe that it will key cleanly and chirp free, even up there. The 6AG7 has more transconductance and better screening of the plate from the control grid. The power dissipation of the plate is similar enough that the power should be about the same. Many of the really old rigs used a 6V6 for a crystal oscillator to drive a larger tube like a 6L6 or 807. The 6AG7 came along later, resulting in better drive, stability, and lower crystal current.


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