The PA neutralization procedure as described in the tuning section of the above transmitter is intended for use during the initial tune up of the transmitter. The step by step instructions does not provide simple explanation to the reader of a way to re-neutralize or to confirm the neutralization adjustment of an operating transmitter.

The following explanation will clarify the procedures of neutralizing your transmitter and includes alternative methods of disabling the plate voltage to facilitate this procedure.

NOTE: Prior to performing any of the steps described below, carefully examine the condition of the grounding hooks provided with the transmitter. Make sure the cable is intact and that good electrical connections exist at the hook and at the point where the cable is grounded to the transmitter frame.

Hang the hook on the connections of any components or touch the connections firmly with the grounding hook before you attempt to remove (or replace) any components or perform any adjustment.

NEVER PRESUME UPON SAFETY

Connect a dummy load and wattmeter (0 to 15 watt, 50 ohm) to the PA output line, using a reducer cone (MI-27791K-5A) and a short length (6-ft.) of RG-8U cable with appropriate connectors.

Remove and carefully lay aside resistors 1R13, 1R14, 1R15 and 1R16 to remove PA screen voltage and to open the PA screen path to ground. Set the multimeter switch 1S2 to some other position than to the PA Eg2 position during the neutralization procedure.

Remove and lay aside resistor 1R9 and replace with 1R13 or 1R14 (6300 ohms) previously removed in step 1. Set the Driver Screen Control 1R38 to the center of its range.

PA plate voltage can be removed by either of the two methods that follow. The first method is "easier on the transmitter" than the second, but is more time consuming.

Disconnect the primary connections to 3T1 (the high voltage plate transformer). Tape the exposed connectors at the ends of the disconnected wires to prevent short circuits between the wires and from grounding out against the transmitter frame.

            OR ALTERNATIVELY

Remove and lay aside resistor 1R25.

NOTE: If this method is used, the PA plate voltage meter needle will indicate off scale when power is applied. This is not harmful to the meter.

Set switch 1S13 to the "disable" position.

Depress the transmitter on and plate on pushbuttons. After the plate time delay relay cycles, applying plate voltage, readjust driver tuning control 1C112 for minimum driver cathode current. Set multimetter switch 1S2 to the PA Ig position. If a grid current indication is noted, adjust both 1C112 and 1C123 for maximum indication. (If no grid current is apparent initially, operate the power raise pushbutton as required to initiate grid current)

Using the power raise / power lower pushbuttons, establish a reference value PA grid current. A reading of 35 milliamperes is a convenient value. This reference value should be held constant during the neutralization procedure.

The small wattmeter connected at the PA output now indicates feed-through power (power coupled from the PA grid circuit to PA output circuit through the feed-through capacitance of the PA tube).

Adjust PA plate tuning control 1L105 and PA output loading control 1L106 for a peak in the wattmeter indication.

Remove power from the transmitter. Adjust the front neutralizing slide (part of PA tube socket assembly) 3/8 inch to the right. Reapply power, adjust 1L105 and 1L106,and note the change in the wattmeter reading. If the meter reading has decreased, repeat this procedure until a minimum wattmeter reading is obtained. If the meter reading increased, move the neutralizing slide to the left and repeat. If an appreciable movement is required at the front neutralizing slide, all four slides should be adjusted so that they are approximately balanced. If necessary, one of the semi-fixed slides may be removed.

Note that the reflectometer meter is not sufficiently sensitive and cannot be used in place of the wattmeter specified in step one.

Depress and hold the power lower pushbutton until the driver Eg2 indication is zero, then remove all power.

After completion of neutralization of the PA stage, replace resistors 1R9, 1R13, 1R14, 1R15 and 1R17 in their normal mounting positions.

If method 4A was used to remove plate voltage, reconnect the primary leads of the high voltage transformer 3T1 (refer to table 3). Tighten connections securely.

                    OR ALTERNATIVELY

Disconnect the dummy load and wattmeter and reconnect the PA output line as before. Tighten the coaxial connections securely.

This completes the neutralization procedure.