Cooling Techniques in Transmitter
COOLING TECHNIQUES
IN TRANSMITTER
Introduction
In modern A.M. transmitters power valves are used in the PA and modulator stages, which are condensed vapour cooled ceramic tetrodes. In the old generation transmittes, triodes are used in the PA, modulator and exciter stages. Both the tetrodes and triodes tubes are capable of being operated at high voltages (11 kV DC) and large anode current of the order of 50 Amps. They also draw large filament current of about 620 Anps at 24 volt CQK-350. Hence the tubes dissipate large amount of power which require effective cooling.
The CQK series of transmitting tubes are tetrode specially designed for transmitters and power amplifiers used in broadcasting.
The tube is installed vertically with the heating connections at the bottom. Handle and transport the tube with utmost care : vibrations and external impacts can cause invisible damage. Avoid sudden movement. Slowly insert the tube in the connection head so that sudden impact is avoided. If the dead weight of the tube is not sufficiently to overcome contact resistance in the connection head, apply gentle pressure. The ceramic parts must be always kept clean. If necessary, they should be cleaned with alcohol or acetone but no circumstances should they be rubbed with emery paper.
The contact surfaces are coated with a heat resistant lubricant film, which does not attack silver. Electrical connections and connection head are provided with contact rings for all electrodes including the anode. The connection head is stationary. It supports and locate the tube, which can be inserted into the connection head only in a certain position. This position is determined by the guide groove on the anode.
Cathodes
All the ceramic tetrodes used in AIR transmitters are directly heated thoriated tungsten cathode. The filament voltage should not vary beyond +5% of the rated filament voltage. The filament voltage must always be measured at the concentric
IN TRANSMITTER
Introduction
In modern A.M. transmitters power valves are used in the PA and modulator stages, which are condensed vapour cooled ceramic tetrodes. In the old generation transmittes, triodes are used in the PA, modulator and exciter stages. Both the tetrodes and triodes tubes are capable of being operated at high voltages (11 kV DC) and large anode current of the order of 50 Amps. They also draw large filament current of about 620 Anps at 24 volt CQK-350. Hence the tubes dissipate large amount of power which require effective cooling.
The CQK series of transmitting tubes are tetrode specially designed for transmitters and power amplifiers used in broadcasting.
The tube is installed vertically with the heating connections at the bottom. Handle and transport the tube with utmost care : vibrations and external impacts can cause invisible damage. Avoid sudden movement. Slowly insert the tube in the connection head so that sudden impact is avoided. If the dead weight of the tube is not sufficiently to overcome contact resistance in the connection head, apply gentle pressure. The ceramic parts must be always kept clean. If necessary, they should be cleaned with alcohol or acetone but no circumstances should they be rubbed with emery paper.
The contact surfaces are coated with a heat resistant lubricant film, which does not attack silver. Electrical connections and connection head are provided with contact rings for all electrodes including the anode. The connection head is stationary. It supports and locate the tube, which can be inserted into the connection head only in a certain position. This position is determined by the guide groove on the anode.
Cathodes
All the ceramic tetrodes used in AIR transmitters are directly heated thoriated tungsten cathode. The filament voltage should not vary beyond +5% of the rated filament voltage. The filament voltage must always be measured at the concentric