This is Millen's very first HF transmitter. Based on a transmitter published in
QST November 1940 by Don H. Mix, as "A Simple Two-Tube Exciter". It also
made its appearance in several editions of the ARRL Handbook for the early 40's.|
Utalizing a 6L6 Tri-tet oscillator circuit feeding a 807 doubler/amplifier. The Tri-tet oscillator was choosen because of its ability to supply output at harmonic frequencies of the crystal, as well as at the fundamental. Filament and DC voltages are supplied by a remote power supply.
On the front panel from left side are the crystal socket with associated switch to short out the Tri-tet cathode circuit when the oscillator is running straight through. The adjacent knob controls oscillator plate current. Placed center is the operations current meter and to its right is the amplifier plate tuning control knob. On the far right is the meter switch to select either oscillator current or final plate current monitoring.
The transmitter pictured above belongs to John Brewer WB5OAU/4. His manual, which is specific to this serial numbered unit, has a manufacturing date of March 1947. However, this same transmitter appeared in Millen ads into the early 50's when it was replaced by the improved version 90801. If you don't have access to the original QST or handbooks which describe this transmitter a wonderful article by Jim Hanlon W8KGI appears in the May 1995 issue of Electric Radio magazine.