AN~GRR-5

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Power Hookups

The AN/GRR-5 Radio has an exceptionally flexible power input specification. This radio can operate on 6, 12, or 24 Volts DC as well as 115 Volts AC. The voltage is determined by a switch on the front of the power supply or automatically in the case of 115 Volts AC.

hookups for each power range is made by different pins on the J103 Power plug. They are as follows:

6, 12, 24 Volts DC

Pin C - Ground

Pin B - 6, 12, 24 Volts DC

115 Volts AC

Pin D - AC

Pin A - AC

Grounding and Shock Hazards when in AC Power Mode
The AN/GRR-5 and similar era radios have a tendency to have voltage on the radio case when powered by AC sources. This is due to the lack of a ground lug on the factory power cord, and filter capacitors inside the radio that are connected to the radio case. This voltage can cause an uncomfortable shock, although its usually not fatal. Solutions can be found below in "Recommended Modifications" to remedy this.

Recommended Modifications

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Add a Grounded Power Cable

Replace the factory 2 conductor plug and cord with a modern 3 prong grounded plug. To do this, unsolder the factory plug from the power cord and replace it with a modern, 3 plug type. Use the following pinout for hookups:

115 Volts AC

Pin A - AC

Pin C - Ground

Pin D - AC

Replace Defunct Selenium Rectifiers with modern components

There are a couple key components that are often defunct that can be replaced with modern equivalents. Rectifiers and Diodes of the time used Selenium. This material easily degrades and is often the cause of a non-working radio. If they are not working they should be replaced with modern components. Modern components are often not a direct replacement. Selenium components often had high resistance, the voltage that the downline components saw was often designed with this in mind. The resistance in modern components is minimal, and it may be necessary to install resistors to simulate the same characteristics as the old ones.

Replace the Selenium Bridge Rectifier with a modern equivalent

My rectifier was blown, but i generally will look carefully at replacing these any chance i get, even NOS parts are usually no good. Just replace with a modern one.

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  Factory Power Supply (Red arrow shows selenium rectifier)

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  Detail of CR101 Selenium Rectifier

Relocate and replace the In case diodes with modern ones inside the power supply

This was originally required because the pins on the power cable connecting the power supply to the receiver were broken, but it also served as a nice way to get rid of the selenium diodes inside the case. I removed the need for the case diodes, by replacing them with modern equivalents inside the power supply itself.

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  Selenium Diodes in Cabinet

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  Detail of CR102 Rectifier in Cabinet

Modified Power Supply with Both Changes

Additional Files

TM 11-295

Radio Receiving Set

AN/GRR-5

August 1952