K)mf 250V

FT7 rn

Fig. 4. Power supply for the converted 5CR-522.

and about 3 inches long. This terminal board and the power transformer are mounted to the chassis with standoffs as shown in the photograph. Although the schematic indicates the use of a small choke, the total current drain of this supply is only 6 mils, so a 2 watt carbon resistor (about 2000 ohms) could be substituted in place of the choke with almost no difference in 60 cycle filtering, In the supply shown in the photographs, the output voltage is just about —150 volts. With different parts, the voltage may differ somewhat and it will be necessary to use a voltage divider on the output to obtain —150 volts.

Two 6 lug terminal strips (H. H. Smith type 3006) are installed in the bottom of the chassis adjacent to the 832A tripler/driver stage and all power and control wiring is brought to these points. This may seem like gilding the lily, but it aids immeasurably in wiring and in any maintenance that might be required at a later date. I might also add that neatness and appearance are considerably improved. All of the power and control circuitry is wired as illustrated in Fig. 4.

Basically, the modernized —522 transmitter is controlled b> two toggle switches; one for filament and bias supply contra!, the other for the transmit/receive function. Note that although the wiring for these switches is shown in Fig. 4, there is no pilot light shown for the transmit/receive function. This is because the "transmit" pilot light is wired in parallel with the antenna relay and is powered from the same 115 volt source. The filament switch is a standard DPST toggle, but the transmit receive switch is a 4PDT unit. This latter toggle switch (Arrow-Hart & Hegeman type 82636) is rather expensive but it is still less costly than the SPS'i toggle switch and 115 volt relay required to do the same job. A rotary switch could be used in this position at a slightly lower cost.

The entire transmitter chassis is mounted on a standard 19 inch aluminum rack panel as laid out in Fig. 7, Although a fourteen inch panel is shown here, a smaller panel may be used with only slight sacrifice in usable panel space; it just happens that this panel was available at the time the conversion was made-Three-quarter inch long, % inch diameter phenolic spacers (II. 11, Smith type 2143) are used between the panel and the chassis to provide clearance for the various mounting screws and hardware on the face of the chassis. The four square variable capacitor shafts are disconnected from the ratchet mechanism, cut off at the machined shoulder, and extended through the panel with standard "ii to !T shaft extenders (H, H. Smith type

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