BROADCAST
TRANSMITTERS
DEDICATED TO THE CONTINUED SUPPORT OF RCA BROADCAST TRANSMITTERS
|
DEDICATED TO THE CONTINUED SUPPORT OF RCA BROADCAST TRANSMITTERS
|
RCA Power TubesCermolox® power tetrodes are used in RCA TV transmitters. When RCA Broadcast went out of business in 1985, the Power Tube division located in Lancaster, PA was sold to Burle Industries. The same plant, together with the same people and materials continued to produce the same tubes, now branded Burle. In 1994, to assure the continued support of RCA transmitters Comark (now Thomcast Communications Inc.) negotiated with Burle Industries to distribute tubes branded with the RCA logo. We Stock the following Tubes 8984 9007 8976 8977 8916 8891 8890 8791V1
Call 800-363-4065 or 413-569-6753 for quote
* The RCA brand 8791V1 is manufactured to our specifications for better balanced operation in the VIPA of the FL-Line transmitter. ** See set up procedure on FL Transmitter main page or refer to TB-TV-1115 *** With a black and sync picture, multiply the Plate Current by the Plate Voltage and subtract the Black level power (peak power divided by 1.68) the transmitter is making into the test load. The end result should not exceed the maximum plate dissipation in the table above. Example: A 30 kW (peak power) G-Line using a 9007 tube in the final. Black Level Power = 30,000 / 1.68 = 17,857 Plate Voltage X Plate Current = 8000 X 4.5A = 36,000 Plate Dissipation = 36,000 - 17857 = 18,143 which is below the maximum 20 kW. Dissipation is directly related to the amount of cooling applied. The figures in the table above assume the air flow is correct according to the RCA manual.
Important Initial set up procedures To assure correct operation and longer life, tubes should be set up correctly upon initial installation. All DC voltages to the tube should be normal. Plate Voltage, Screen Voltage, Filament Voltage. With NO RF drive applied, set the Static Plate Current to the correct value by adjusting the bias voltage. (See table above for your reference). First 200 hours of operation. Initially the filament voltage should be set to the nominal value stated in the tube data sheet (see table above for your reference). Operate the tube at this voltage for a minimum of 200 hours. After 200 hours. In the case of a visual tube, reduce the voltage slowly while observing the sync pulse amplitude on a waveform monitor. As soon as the sync pulse begin to compress, increase the filament voltage by 1/10 of a volt. Check the frequency response across the band for correct tuning and check the DC Plate dissipation does not exceed the tube specification. In the case of an aural tube, after 200 hours, decrease the filament voltage until the output power begins to drop, then increase the voltage by 1/10 of a volt. Filament Life The emission of the thoriated tungsten filament in a power tube is dependent on a monolayer of thorium on the surface of the wire. This layer is formed by the reaction of carbon with thoria. The end of tube life occurs when all the carbon is depleted from the filament structure. The physics of the filament are illustrated by the fact that theoretically for every 3% increase in filament voltage (0.3 volts in the case of a 10 volt filament) there is an increase of 20° Kelvin in the temperature of the filament, a 20% increase in peak emission and a 50% decrease in tube life. It can be seen that it is important to run the filament voltage as low as possible to support the emission required to produce the output power but only after the initial 200 hours required to fully activate the thoria. If the filament voltage is set too low to begin with, it may not provide sufficient emission when required to do so later as the tube ages.
|