Ameritron UnRS-AL12U Antenna Relay Replacement for AL80A AL1200

As the original AL1200 (and many other amplifiers) designer, I will be releasing updated parts and boards for several classic amplifiers. Please check our other eBay listings. This fully-sequenced universal relay system replaces the pre-2008 standard AL1200, AL1500, AL82, AL80A, and Heathkit SB1000 amplifier open-frame T/R relays. It also replaces all post-2008 cube relay systems in the large AL1200 style amplifiers. It does NOT fit AL80B amplifiers. This board draws 100mA @ 15Vdc nominal. This board improves all original relay system

specifications. The input contact is an 8-ampere rated gold flash contact. The output relay uses two parallel 8-ampere gold flash contacts. The use of parallel contacts simulates a bifurcated relay style, greatly increasing power handling and reliability. The relays are carefully selected for RF power applications with low stray capacitance and no measurable affect on SWR. Other than mounting, this board is a direct swap for any Heathkit SB1000 or Ameritron AL80A, AL1200, AL82, or AL1500 amplifier (the AL12X frame) relay. This system reduces relay switching time over most stock open-frame relays by nearly 50%. The UnRS-AL12U is slightly faster than the Ameritron cube relay board. The AL12X frame (AL1200, AL82, AL1500) Ameritron series used two different relay systems. This board directly replaces both AL12X frame styles The original single open-frame relay systems used a factory-modified open-frame 3PDT 12Vdc 100mA relay. Three suppliers were used, Deltrol, Midtex, and P&B. With open frame relays, a 12Vdc (small yellow wire) from the meter board is switched by the standby-operate switch. This switched 12Vdc runs through the Operate or Transmit LED and a parallel resistor by a red/white wire to the relay positive. A blue wire from the rear panel RELAY jack grounds the negative relay coil terminal to close the relay for transmitting.SB1000 Heathkit and AL80A Ameritron (I designed them both) relays use similar wiring. Newer AL12s (AL82, AL1200, AL1500) after ~2005 use a printed circuit board relay system (figure 4). While some wiring overlaps, the red/white wire and LED resistor wiring changes. A new 28-volt line is added. The newer Ameritron AL12X frame relay circuit board requires both 28Vdc and 14Vdc. Rather than update the circuit board, MFJ “dead-bugged” a new full-wave voltage doubler onto the original 1983 bridge rectifier metering board. This doubler provides around 14Vdc and 28Vdc. This newer (post-2008) cube relay board system has a modest value resistor in series with the LED. The Standby/Operate switch still adds and removes 14-volts to the LED to switch the amplifier in and out of operation. The LED and standby wiring remains as original with the UnRS-AL12U kit. Do not change the LED wiring or the metering board wiring when installing this assembly. If you are not comfortable with neat soldering, please find help. RF and control connections must be solidly made! 73 Tom W8JI