Front Panel	Top View

This is the preliminary layout of the Power Supply.

It will contain the main 130 volt supply and several other sources of DC for all peripheral circuits. I am however intent on designing a significantly different power supply system from those employed by other builders. This will be a regulated supply and will not be powered down during receive, it will be "switched" off however, as will be explained further on. The front panel will provide HV Voltage and Current metering as well as adjustments, Low Voltage Supply fuse holders, main circuit breaker and indicator lights.

Most other builders have been incorporating the lower voltage supplies required for various sub stages into the particular units themselves. For example, the modulator requires a 12 volt supply which floats off ground to supply operating voltage to the FET driver devices. This is required since the modulator operates as a Source Follower supply to the RF deck. Since the driver of the modulator functions by switching the gate voltage relative to the source, it must therefore float up and down as the source voltage varies. It would seem that floating the supply directly inside modulator deck using the magnetic coupling of a small power transformer to isolate the supply from ground is a logical one. But this requires bringing 110 or 220 volts AC into the modulator deck. This is something I'd rather avoid in both the RF and Modulator Deck entirely. I should be able to just as easily provide a clean source of floating filtered DC from the main power supply using a common mains switching system. By doing so, I can more easily provide common saftey cutoff system should one supply fail.

The other, and more signficant, departure from convention will be in the design of the primary DC voltage supplied to the modulator and subsequently to the RF deck. Current convention calls for this supply to be a rectified, filtered and unregulated DC supply from the secondary of a suitable power transformer. Under load this voltage should be maintained at about 130 volts by the load in conjunction with the various voltage drops occurring across several supply components. This requires a secondary voltage of about 105 volts and that AC be cuttoff during receive to avoid surging of the voltage in the filter bank. The DC from the filter bank is also cut off for good measure. This provides an optimum condition for conserving power during standby but also requires several heavy relays and some protection ("step start" or "soft start") circuits to prevent initial surge currents from exceeding safe limits.

I would prefer to have as few heavy switching devices as possible and be able to utilize commonly available 1:1 or 2:1 power (isolation) transformers. Hence, I am designing a voltage regulation circuit which operates on the rectifier side of the filter bank using SCR technology and a inductive input filter much like switching regulator. This regulation would accomodate both soft start and full load regulation and produce only negligible power consumption (the unloaded transformer and control circuitry) during standby.

Soft start: I've greatly simplified my design and construction by utilizing a conventional step-start resistance in the primary of the HV transformer. However, this is not a time delay device. Rather, it will only close if, and when, the supply filters have reached a pre-determined voltage. Doing this prevents full load being applied if there is a shorted supply problem. In the event of a short the step-start resistor will be abruptly and demonstrably sacrificed in lieu of other (more expensive) components.

A fully detailed schematic will be posted as details evolve. However the basic circuit below has been tested and works well. A few tweeks should result in a very adequate supply.

Preliminary Regulator Schematic
Updates pending.

Here's some more images of the completed work as of 4/21/10
Click on images for full size detail

This is the front panel in finished paint, black appliance epoxy.	This is the low voltage side of the supply. Transformer has two output windings, one floating driver supply and +/- 12 volt supply. AC voltage select block (120/240V) is on top of low voltage xfmr.	This is the rectifier block for all supply voltages. Likely the hottest part of the entire project.
This SCR and Diode comprise the regulator block. They are bolted to the input side of the supply filter inductor.	This better shows the control harness terminal strip. The step-start relay is in the corner. Step-start resitor is under the lip of the front panel.	This is the regulator "module". The entire heat sink is mounted on Lexan since it has 170 rect. AC on it.
30 Amp AC input filter is mounted under the regulator module, between the Lexan standoffs.	Laced wiring runs down each side to rear panel. Lacing really "neatens" up a project. IMHO	Regulator control board, low voltage fuses and all input/output will be on rear panel.
Low Voltage Supply Caps Bracket