<p>2. POWER SUPPLIES</p><p>Units referred to as 48 VDC "Blade Server" power supplies are readily available on the surplus market and provide a popular source of power for these amplifiers. In particular, the Hewlett Packard (aka Compaq) 3 kw BL20p switching power supply, often is identified by its HP part number of 226519-001 and/or its spare part number of 253232-001. Here are the specifications for this particular power supply module. They each weigh about 15 pounds, and are 2.75" wide x 4.875" high x 22.25" long. They are designed to provide a very healthy 57 amps of power at 51.4 VDC.</p><p>An upside down rear photo of one of these HPS3KW power supplies is shown at the upper right. Notice that the three lower center control pins have been shorted to enable the unit to operate when plugged into 230 VAC. Flat blade push-on spade connectors have been installed on the DC output leads and are shown ready for wiring. The photo below shows the power supply wired and ready for installation. Notice that the output wires have been bifilar wound on a ferrite core, and both sets of terminals are used for all connections.</p><p>The AC input</p><p> terminals are at the bottom. Neutral is connected to the left two terminals, the two center terminals are grounded, and 230 VAC is connected to the right two terminals. If you are like most of us in North America, they also can be operated by connecting each of the two opposite phase 115 VAC lines to the outer two terminals (to provide 230 VAC between the two of them) and grounding the center two terminals. In other words, the center two terminals are grounded and 230 VAC is applied to the outer pairs of terminals.</p><p>These power supplies have been reported to generate RF noise (although I have not noticed it here), so you should be prepared to ground the cases well, and wind the output DC leads together around suitable toroids with a ferrite mix that will be effective at 50 MHz. Something similar to the Palomar F-140 Core with Mix 43 or the Fair-rite Part # 2646804502 Mix 46 (what I used here) should permit a number of bifilar turns and be a good place to start. </p>