GE MASTR Progress Line model 4EP38A12 AC Power Supply documentation.

The 4EP38A10 Power Supply is similar, very similar, to the 4EP38A12. The difference is that two medium-sized printed circuit boards in the model 4EP38A12 replace hand-wiring found in the GE model 4EP38A10 in the DC power supply section of the 4EP38 Power Supply model series.

The GE Mastr Pro 4EP38 series of power supplies provide all required DC voltages as well as the required forced-air cooling to operate any GE Mastr Pro series Receiver and Transmitter 'strip' in continuous duty applications such as commercial dispatch or commercial repeater operation. In ICAS and amateur operation the life of this equipment can be even longer; shelf-life of components, however, becomes a bigger concern than the usual wear-out failure due to use.

GE Mastr Pro 'strips' have been manufactured for mobile use as well as use on the 4EP38 model series of AC Power Supplies. The following list of available strips was compiled from various GE manuals:

• VHF Low-band, 25 - 50 MHz in three freq ranges: 25-33, 33-42, 42-50, with the top range modifiable to 6 Meters
• VHF High-band, 144 - 174 MHz in several frequency ranges and
• UHF in two frequency ranges: 406-420 and 450-470 MHz. Strips in the latter range can be used on the 440 MHz Amateur band.

Click here for a full size page of the first page of the technical manual which details the sepcifcations of the 4EP38A12 Power Supply.

Outline diagrams, front and back of the 4EP38A12

Outline Diagram Front Click

Outline Diagram Rear Click

Electrical Schematic Diagram 4EP38A12 Click

Electrical Schematic Diagram 4EP38A10 - planned

Front view of GE Mastr Pro 4EP38A12 with Low-band VHF (25-50 MHz) 'strips' in place.

• Transmitter strip is on top. Note also that the top cover is removed to allow viewing of the transmitter internals.
• 'Duct work' occupies the center.
  - The square box with holes in it is a speaker in this picture - some models don't have this.
  - The 'duct work' is fed by a muffin fan on the right side of the chassis
• The Receiver strip is on the bottom. Note also that the top cover is removed to allow viewing of the receiver internals; one internal shield, over the 1st and 2nd RF Amplifiers and First Mixer, has also been removed.

Angled front-view of GE Mastr Pro 4EP38A12 power supply.

The speaker box's shape can now be clearly seen.

Local operator control of the GE Mastr Pro is via the On/Off switch, Mic, volume and carrier squelch controls accessable on the left side of the chassis.

From top to bottom, those controls are:

• Microphone connector,
• AC Line Fuse,
• AC power switch,
• Squelch control and
• Volume control.

Another angled front-view of GE Mastr Pro 4EP38A12 power supply.

This view gives a better view of the 'duct work' that carries the forced-air cooling from the muffin fan (on the other side of the chassis) past the Transmitter strip.

The multi-conductor connector that mates the 4EP38A12 power supply to the Receiver strip can also be seen in this picture.

This view looks into the duct work - several power transistors can be seen mounted on the duct work proper, making the duct work act as a heat sink for those devices.

This picture also shows the Receiver connector from the 4EP38A12 Power Supply to the Receiver strip.

Rear view of the 4EP38A12 power supply.

Connections to the 4EP38 series of Power Supplies are made via two terminal barrier strips along the top edge of the rear of the 4EP38A12 Power Supply chasis. The following connections are available for interface:

• AC 117 Volt Power input
• Receiver audio output,
  both a
  - speaker output and a
  - low-level, non-demphasised output from across the volume control
  are available.
• COS, "Carrier Operated Switch", a logic-level indicating the carrier squelch's state.
• Transmitter audio input, actuated via 'diode' switching through a 5 K resistor and 10 Volts DC
• Transmitter keying via actuation of the high and low voltage DC T/R relays in the 4EP38A12 Power Supply

The board on the far right, with the two smaller double-row terminal barrier strips, is a custom interface board I designed that includes a de-emphasis network for the receiver, a 'driver' that keys the T/R relays in the 4EP38A12 from a low-drive capability logic-level output from a repeater controller. Also included are audio level adjustments 'pots' for setting audio levels into and out of the 4EP38A12 Power Supply and the currently mounted Receiver and Transmitter strips.

Angled rear-view of the 4EP38A12 power supply.

Both the Receiver and Transmitter strips 'swing' out on hinges alowing wasy access to the rear of each one's respective chassis.

Shown here is the Transmitter strip swung out.