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(c) Sindre TORP
R. L. Drake
Co.
AC-3
and AC-4 Power Supply Test Fixture
By Bill Frost
The AC-3 and AC-4 Power Supply test fixture was built by the R. L. Drake Co. Engineering Department to test new power supplies, as they come off the assembly line. When the T-4XC transmitter and the TR-4CWw/RIT transceiver were discontinued and production of the AC-4 power supply ceased, the test fixture was willed to the Service Department.
The power supply, to be tested, was connected to the 12-pin connector and the 110 VAC socket in the lower right corner of the test fixture. Incidentally, the 12-pin connector was actually replaced very few times even though it really got a workout. It wasn’t replaced until you could no longer "jiggle " the power supply connector to make reliable contact.
The four meters on the left side measured the + 250 volt section (RECEIVER), the +650 volt section (TRANSMITTER), the bias voltage, and the filament voltage. The variac allowed the operator to control the line voltage, while watching the lights and meters for signs of trouble.
One of the two fuse holders, in the lower left corner of the fixture, was in the + 250 volt line and other was in the + 650 volt line. These two fuses have saved many a filter capacitor and several pair of clean underwear. The switch on the right of the two fuse holders was used to turn the power supply on and off. The red lamp to the right of the on/off switch was an indicator to test the continuity of the TR-3 and TR-4 speaker lead. Inserting a shorted plug in the 6-inch pigtail would cause the lamp to glow if the speaker line had continuity.
The slide switch to the right of the speaker lead test lamp allowed the power supply to be started at a lower than normal line voltage level. This allowed the power supply to be initially tested at a low line voltage level before applying the full 110VAC.
The toggle switch to the right of the low start switch permitted the technician to apply a load to the 650 volt section of the power supply. This provided a very effective means to test the electrolytic filter capacitors, in the +650 volt section, for AC ripple. Electrolytic filter capacitors may not become leaky until they are placed under a load, this test provided that necessary load.
The orange indicator to the right of the toggle switch was illuminated when a shorted plug was inserted in the VOX RELAY jack of the power supply. This provided an easy continuity check of the relay control lines in the power supply used to energize a linear amplifier.
The jack below the low voltage start switch was provided for a volt ohmmeter. The VTVM was used to measure the AC ripple of the electrolytic filter capacitors. The rotary switch to the right of the jack provided a selection between the various power supply sections. Some of the press on labels are missing in the picture, as the switch had more positions than shown. This feature of the test fixture was very beneficial to the service department when testing an older power supply.
The lamp, above the transmitter on/off switch, illuminated when a shorted plug was inserted in the AGC jack of the power supply. This provided a means to test continuity of the lines between the AGC jack and the 12-pin power connector.
The two lamps above the AGC indicator were "line short" lamps. In the unlikely event a wiring error was made by the assembler, the wiring error could cause an excessive load on the 110 VAC power source. The lamps would glow brilliantly indicating to the test technician that the power supply had a problem. The toggle switch above the two "line short" lamps inserted a 100 watt light bulb in the circuit to take the bulk of the 110 VAC power source. This enabled the technician to trouble shoot the power supply with a "line short" while still having the 110 VAC power applied to the power supply.
Once the "line short" had been found, the large knob of the variac allowed the operator to resume the test, starting at a very low line voltage and slowly increasing the 110 VAC power being applied to the power supply in test. This allowed the operator to monitor the meters and lamps to ensure he/she had indeed found the trouble before applying the full 110 VAC. The meter above the knob provided a means of measuring the actual voltage level being applied to the power supply under test.
A revised test procedure written on July 8, 1966 read as follows:
AC-4 TEST
 | Remove all clippings from power supply, checking for loose wire or solder under condenser mounting plates. | ||||||||
| Inspect unit for cold solder joints, unsoldered joints, unclipped leads, or excessive solder. Inspect for short circuits, incorrect wiring, and loose components. Q-max the nuts holding the VOX connector. | ||||||||
| Inspect the Transformer for the rubber pad. This is placed between the transformer and the chassis. | ||||||||
| Inspect the dual 80/100 mfd condenser and be sure the 100 ohm resistor is connected to the 350 volt side of this condenser. | ||||||||
| Inspect plugs and cables for appearance and tightness of connector. | ||||||||
| Insert 5 amp fuse in holder and plug power supply into test fixture. Put shorting plugs in Vox, AGC, and audio connections. | ||||||||
| Set line volts to 120 and set test switch to start voltage. When power
switch is on, the voltage should be approximately:
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| Turn test switch to high and the readings should be:
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All 3 pilot lights on the tester should be on. | ||||||||
| Rotate bias control checking for varying bias voltage. | ||||||||
| Turn variac to 130 volts and turn switch on and off rapidly for five times. | ||||||||
| Put bottom plate and cover on unit. | ||||||||
| Record serial number and send unit to packaging department. |
The power supply test fixture was used in the service department until October of 1998 when the service department discontinued offering repair service to the older amateur radio equipment. If you are using a piece of 4-line equipment, your power supply was at one time final tested on this piece of test equipment.
Bill Frost
R. L. Drake Co.
