Authored by VE3EFJ
5.0 AC4 POWER SUPPLIES
There is little difference between the AC4 and the AC3 power supplies. If you need new rectifier diodes, 1N4007 will do nicely. For the price of these diodes, there is little point in buying anything else other than the '7s. I would also advise shunting each diode with a 1 meg 1/2 watt resistor to voltage balance the diodes.
Pay particular attention to the -ve bias supply in these units, for it is critical to the operation of the transmitters and ESPECIALLY the transceivers. A weak bias supply will adversely affect the receive section of the transceivers, for it is used for the AGC. The bias supply is not used on the transceivers for cut off bias to the unused sections between receive and transmit. The cathodes are lifted off ground by the T/R relay.
If you are stuck for a supply, a Heath HP20 or HP23 will work with some minor changes.
NEVER ship a power supply inside an MS/4. The weight of the supply combined with the typical banging around packages get will trash the MS/4.
The connector on the side of the power supply is an external relay contact for such things as power amplifier switching. This connector is no longer available and Drake will supply a phono connector and adaptor plate for it, or you can make one up yourself. If you use a phono connector, note that one side of the switch contact will be on ground (chassis).
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