The M-1070 is a 6 or 12VDC -or- 117VAC power supply for the AF-67 and AF-68 mobile transmitters and PMR-7 and PMR-8 mobile receivers.
I have 2 M-1070s that have been modified. The 6 and 12VDC components have been removed for 120VAC only use. M-1070 #1 is used for a AF-68 and PMR-8 station. M-1070 #2 will be used for a A54 Transmitter and its matching PMR-6 receiver. ( See: August2025-QRZ.pdf pg 76 ) FWIW factoid: My Elmac radios use 12VAC Filament voltage. This article depicts the refurbishment and modifications I made to Supply #2.
What's that color? ACE Hardware BBQ Black. The rear of the supply sports an IEC AC connector- where a computer AC cable can easily be plugged in. No more AC cord dangling and in the way when moving the supply from table to table. The Brass Wing Nut is for bonding to the center of the stations Star Ground. The 12VDC Antenna Changeover relay plugs into the RCA Jack
Front of the supply has AC Power ON-OFF with Green Indicator LED... and the TX ON switch that operates internal RY-202 relay as well as the Blue Plastic Aux relay (shown below) that operates the Antenna change over relay. The RED TX ON LED is a visual reminder.
This photo shows the top of the supply where the Can Capacitors have been removed and covered with scrap Printed Circuit Board material. If you squint, perhaps you can see a Blue LED next to the green heat shrink tubing. The LED and 1K resistor are wired across the transformers 12VAC output lugs. An unnecessary visual indicator.
In the upper R corner--- is the RX-TX relay, RY-202 that switches +250 VDC from RXer to the TXer- as well as turns on the +500V for the TXer. The original relays past performance has been poor, so a beefer relay was substituted.
The Blue 100 ohm @ 10W power resistor is used to adjust both output voltages. Schematic shows 50 ohms, but for some reason this supply came with 100 ohms. 100 ohms provides an output of +600 and +300 VDC, NO LOAD. At almost full load it becomes +550 and +250 VDC.
To the R of the Blue 100 ohm are 2 tubular 20K resistors in parallel acting as a bleeder resistor across the +300VDC output.
Below the Blue 100 ohm are 2 capacitors labeled HV HV. These are 47 mfd @ 450VDC in series with 100K ohm balancing resistors across each capacitor. The second capacitor is shrouded with a piece of Heat Shrink tubing to protect it from touching the chassis.
The Caps labeled LV LV are 47 mfd @ 450VC in a Pi Network configuration with the original Elmac filter choke wired between them.
The lower terminal strip with the Yellow Wires were for the Vibrator connections. Now they provide AC volts to supply a DC supply which outputs approx. 14VDC for 12V relay operation. Note: Experimentation is required to choose the correct terminal lugs for your DC supply's desired output.
The Blue Plastic Relay operates on 12V and is used to switch the 12VDC supply that feeds the Antenna Relay RCA jack. This relay is operated via the TX ON toggle switch on the Front Panel and via a wire that is part of the umbilical cable that feeds the Transmitter.
To the R of the Blue Relay is the 120VAC IEC connector. Note the 2 blue disk Safety Caps.
The above M-1070 schematic does not depict all of my wiring changes. In fact, it leaves out how the 120VAC is connected as well as other odd ball modifications. Of course... your needs are likely much different than mine.
The OB-2 VR tube for 105 VDC was omitted because the TX and RX have their own VR tubes to feed their VFOs. Note the Yellow Circled resistor in the full wave bridge diode network- replace it with a short circuit for max DC volts out or adjust it to suit your desired output voltage. I tried 150 ohms, and the Low DC volts were too low. 100 ohms worked the best for me.
Got a question about this project? email: 599kr7w@gmail.com
End of Blog Post. Thanks for reading this far.
73 and Keep your Filaments Lit
Ricky KR7W
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