High Power Radio Tubes
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High Power Radio Tubes
A 4-100A vacuum tube is a component used in radio electronics. Sometimes called a beam tetrode, this vacuum tube is used as a power amplifier. Vacuum tubes are used in ham radio transmitters and high power commercial radio and television transmitters instead of transistors because one tube can take the place of many transistors and waste heat is easier to remove with cooling fans.
The number 4 identifies the tube as having four elements inside and 1000 identifies the maximum continuous amount of power dissipated at the tubes anode to be 1000 watts. The 4-1000A is the largest of a series of tetrode tubes manufactured by Eitel-McCullough, Inc.
Physical Construction
The 4-1000A vacuum tube is composed of four internal parts. The anode, cathode, filament and grid are positioned vertically on top of a 5 pin base plug that connects into a socket in the radio chassis. The unit is surrounded by a clear glass shroud.
According to specifications publish by Eitel McCullough, Inc., the tube is 9.25 inches tall and has a diameter of 5 inches. The filament is coated with thorium for long life and operates at 7.2 volts. The anode connection is on the top of the tube.
Uses
A 4-1000 tetrode vacuum tube can be used as a class C power amplifier to increase the RF output power up to 3340 Watts. The weak input current from the microphone or music is amplified to produce a stronger signal for transmission.
A pair of these tubes can be used as an audio signal modulator for an AM transmitter and the 4-1000A can also be used as an oscillator to generate radio frequency signals. According to RCA, the maximum plate current output for the 4-1000A is 700 miliamperes at frequencies of up to 110 Megahertz.
Cooling
Radio tubes generate heat that must be dissipated to prevent damage to the transmitter. The 4-1000A tube requires forced air cooling. The inside of the transmitter is pressurized by a centrifugal fan and air is directed through the specially designed tube socket to cool the filament and grid connections.
According to the Eimac 8166/4-1000A technical data sheet published in March of 1976, an air flow rate of 35 cubic feet per minute is needed when the tube is operated at its maximum rating of 110 Megahertz. The manufacturer recommends using the Eimac SK 500 socket with glass chimney to control airflow around the tube.
wandererh Level 2 Commenter 19 months ago
When you talk about anode, cathode and filament, you really take me back. But I wonder if they really will be much use too much longer as you routinely see specs of hundreds of amperes for semiconductors these days.