SG-500 Smart Power Cube Connections & Use H.F. SOLID STATE AMP 1.8 - 30 MHZ Reviewed by Bob Osterhous W9PSE date:30DEC2003 Recently we secured an SG-500 500 Watt Solid State Amplifier and PS-50 matching power supply at a local ham fest. We were interested in the automatic band switching method for quick change and also that it provided 500 watts approx output which is within 3 DB of a KW amplifier. Having purchased it at a reasonable price we were not too disappointed to find out on testing the unit into a dummy load it was not working. Fortunately I knew the seller and he had a second unit, which was new in the box and let me take it for comparison and testing. Thus by having (2) units and testing into a dummy load I have been working on getting them both on the air. As I use a G5RV 104 Ft. HF antenna that auto-tunes with my ICOM IC-756 pro on all bands 6 thru 80 Meters, I had not anticipated the problems associated with adding an amplifier which only matched 50 ohm, and an approx SWR range of 2:1. Finding out quickly that the amplifier would only load on 20 meters on the G5RV I was fortunate to be able to borrow an a Model MFJ 986 antenna tuner to use with my wire antenna. Now to the connection of the SG-500 to the PS-50 power supply. The manual suggests #6 GA. Wire for the 12 VDC supply. Fortunately I was walking thru one of the Big Box hardware stores and ran across a 4 Wire Range Cord for an electric dryer. This 4 Wire (Red & Black #6 and Green & White # 8) were just what I needed. The 6 Ft.long cable had ring terminals on one end that fit the front of the SG-500 amp perfectly. Cutting off the plug end and attaching screw on terminals that take #6 gauge wire with narrow flat heavy spade lug proved fine to connect to the PS-50 power supply terminals. I used the Green wire for ground and the red for (+) and black for (-). For the input 120/240 to the power supply I likewise found a 6 ft. air conditioner cord which has 14 /3 wire and had a heavy duty, three (3) prong ground plug on one end. After using the amp on test for a short while on a 20 Amp circuit on 115 volt, there was considerable light dimming in my ham station room. Thus we changed the internal jumpers in the PS-50 supply and cut off the plug end of the air conditioner extension and put on our 230 volt polarized plug and connected it to our 230 volt supply with #6 wire. Now on 230 volt supply there is no dimming of lights and the voltage drop on the 12 volt side went from a 4 volt drop to approx 2 volt drop. On 230 the voltage is 17 VDC at the SG-500 input and on 115 V it was 16 volts no load. Note the PS-50 is an unregulated supply with eight 33,000 MFD capacitors and works well. With the heavy cables and 12 volt supply working and not tripping off on the "voltage" led light on the front more tests were made with the antenna and tuner. The SG-500 has operated fine on 15,17,20 meters into the dummy load even with my "Auto-tune" feature turned on with the IC-756 Pro. In reading the ICOM book it says to turn off the "Auto-tune" feature by hitting the button and leaving the light out. This proved necessary to work properly on 40 meters at my station. Thus leaving this "auto-tune" feature off is probably best on all bands when using the amp. The export model is set for operation on 10 meters and works well with slightly less power output of about 300 watts. Use on 40 and 80 meters proved very successful however we did not try it on 160 meters. The SG-500 amplifier can use the "auto turn on" feature, which is keyed by about 10 watts of drive to trigger amplifier. In talking with one mobile station who uses the SG-500 he fixed his for PTT so it keyed up with the transceiver. We fond in working a DX contest that there was some delay time in switching back to receive thru the tuner & amplifier combination and therefore switched ours to work as PTT. I made a small box with a switch to remotely select the amplifier on/off from the operating position, and put a small PC relay (DPDT) relay in the box to provide extra isolation from the transceiver. Also a pilot light on the box verifies when the amplifier is keyed up. Our amp & power supply are down low to the right of the operating desk on the floor and almost out of view. This provided normal operation of the amplifier after the 1st switch on the front panel of amp is moved to the upward position. The switching of the filters and bands still comes on with about 10 watts drive but no delay or problems during normal operation has been found. The different bands can be remote selected by grounding the select terminals on the front of the amplifier if you so desired. Thus adding a 6 pole, selector switch into the box would provide complete remote selection or a 4 pole if you do not use 80 or 160 meters. (The auto-select works so well this is not necessary for normal use) Operation on 15, 17, 20 & 40 meters has been very successful and good reports on audio quality and signal strength have been received on our recent contacts. We keep the drive to about 25 watts which provided approx 400 watts output with good audio. By accident we left the drive at full 100 watts input and audio reports were still good, but a slight amount of interference was noticed from my computer speakers in the same room. With the 25watt drive I have no notice of any TVI, audio problems or telephone interference from my station what so ever! (The same as with the 756 PRO only) We are quite pleased with the operation of this SG-500 amplifier and believe it would be great for mobile as well as base station or emergency communication on other 12 VDC supplies of enough capacity. Other future options include having the transceiver select the proper band filters automatically however at this time it does not seem necessary. Also floating a 100 Amp Hr. battery across the 12 VAC amp input will help if you use it on 115 VAC supply. Likewise a 1 Farad cap, as used on high power auto hi-fi systems might be used to provide a stiffer DC supply although a series limiting resistor might be needed. Regarding the ALC circuit. The ALC is not compatible with ICOM or most popular transceivers that have "negative" ALC, as the SG-500 has positive ALC. DO NOT CONNECT ALC FROM STANDARD TRANCEIVERS. Building an op amp circuit to reverse the negative ALC from a transceiver could be made and put into the remote selector box if desired. The fan kit that mounts on the bottom of the amplifier comes on with temperature rise. On intermittent use the fan does not operate. With high usage or full 500 watt output continuously the fan will start. If no fan is used the amp can trip off in about 1/2 hour of operation in normal use. Some type of fan air circulation should be provided to the amplifier. We like using separate external fans and some type of high/low air circulation could be made to suite the individual installation situation. Thus our extra relay contact in our remote box. The only disadvantage of using an amplifier with an "Auto-tune" transceiver is the necessary use of an antenna tuner if you are using non-resonant antennas. Using one of the SGC auto tuners such as the SG-235 500 watt auto tuner would solve this problem and again provide a completely auto-tuned station for quick frequency and band changes. We hope this information helps you know and use the SG-500 amplifier to it fullest advantages. Also suggest anyone look at eham.net under product reviews on Amps/SG-500 for other peoples ideas etc. IRC reviewBY: Bob Osterhous W9PSE Indianapolis, In.