QST 03/1981

POSITIVE MUTING OF DRAKE TR-4C

This modification provides positive muting of the TR-4C when used in conjunction with an external receiver. PTO dial-lamp switching for the R-4C external receiver is also provided as an operational status indicator. Fi g. 1 illustrates the circuit modifications. C-217 is removed from the TR-4C as are the switch jumpers (dashed lines). Add the phono connector J. as shown in the diagram. If the line to J from the receiver side of the transceiver/receiver switch is made very short, it need not be shielded. Install a cable from J to the PTO lamp jack on the R-4C. The PTO dial lamp on the R-4C is illuminated only when that unit is the active receiver. After modification, you will find that the audio gain on the TR-4C does not have to be turned off when the external receiver is in operation.

William F. Cade, K5HU .Tpelo Mississippi

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Fig. 2 -- These simple changes in the Drake R-4C provide positive muting when using the set in conjunction with an external receiver. J is an added tack. It leedthrouqh capacitors are used to bring the switch leads trough the under chassis rt cage wall, the shielded leads may be replaced by unshielded wire. Likewise, the two 0.001 uF capacitors from these leads to ground may be omitted. The 0. 001 uF capacitor in shunt with J IS needed for proper operation.