Serial no.: 0624

This amplifier is made in Slovakia. It has a GU84B metal ceramic vacuum tube. To obtain full power the amplifier has to be powered by two electric supply phases. Each 2 kilovat power toroidal transformer should be powered from a different electric supply phases. By connecting both supply cables into one electric supply phase we will achieve a high quality kilovat signal, without any spletter. The output has a Pi-L contour, which also reduces the high harmonics and interference from TV and other electronics by about 15 dB. The amplifier's automatics guarantee the GU84B tube a long lifespan. The usual defect of this type of amplifiers is the cooling blower. The blower itself is high quality and does not make any unwanted noise, however you can still hear the air blowing. Because of that after some time the amplifier was slightly modified. In the front panel I mounted an EMKO ESM-3710 temperature controler and in the hot air flow, right above the anode - a temperature sensor. (foto1) The vacuum tube is able to work in a maximum of 200'C temperature. The blower is powered by a 230 Volt power supply straight from the power grid through a 25 watt 230V bulb and a 50'C mechanical thermocontactor mounted on a ceramic wire resistor. (foto2). When turned on, the thermocontactor is cold and the blower is off. After 2-3 minutes the contactor turns on and the blower is powered on and starts to spin quietly. In this setting the vacuum tube does not go above 50'C. In transmission mode the vacuum tube's temperature raises and at a certain point it at which the controler turns on the bulb and the blower is fully powered. Then the vacuum tube is cooled down at maximum. The higher the temperature we adjust on the controler, the less noise will the blower make. I adjusted it to 150 degrees. After switching off the amplifier, the cooler continues to work for 3-4 additional minutes until the thermocontactor cools down completely. The amplifier has a small coefficient of efficiency and heats up even when the vacuum tube is in its idle state. The Anode current is big, above 500 mA. While the SSB is paused there is no anode idle current. It turns on automatically once you start talking into the microphone instead of you clicking the PTT button on the transceiver. However this allows the switch elements to work longer instead of lowering the heating of the amplifier. If we need 300-500 wats we will have to use 1600. That's the price of a high quality output signal .