Tri-tet oscillator

A tri-tet oscillator is a crystal-controlled vacuum tube oscillator. It is an electron-coupled oscillator (ECO), which uses a tetrode or pentode tube.

In an ECO, The screen grid acts as a plate for the triode oscillator. Some of the electrons pass through the screen grid to the plate, causing a current to flow in the load. This effectively isolates the oscillator portion from the load, so that loading does not affect the operating frequency.^[1]

The tri-tet was introduced by James J. Lamb in the June 1933 issue of QST magazine.^[2]

In the schematic shown, the L1/C1 tank circuit control the current through the crystal. It is normally tuned a point between the crystal's fundamental frequency and its first harmonic.

The L2/C2 tank circuit is tuned to the desired harmonic.

D+ acts as the "plate" voltage for the triode, and is slightly less than B+.

References

^ Sterling, Geroge E. 1940. The Radio Manual for Engineers, Inspectors, Students, Operators and Radio Fans. 3rd ed. New York: D. Van Nostrand Company, Inc.
^ Lamb, James J. “A More Stable Crystal Oscillator of High Harmonic Output.” QST June 1933: 30-32.

[1] Sterling, Geroge E. 1940. The Radio Manual for Engineers, Inspectors, Students, Operators and Radio Fans. 3rd ed. New York: D. Van Nostrand Company, Inc.

[2] Lamb, James J. “A More Stable Crystal Oscillator of High Harmonic Output.” QST June 1933: 30-32.

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