Data redazione: 25/07/03
R.V.R. Elettronica S.r.l. (BO)
VJ10000-TE - R.F. Tube Amplifier
20
The limits that mustn't reach are:
- Anode current = 3,6A
- Control grid current G1 = 300mA
- Screen grid current G2 = 300mA
- Output reflected power = 750V with a continuos working of 10KW in antenna
- Anode dissipated thermal power of tetrode > 10KW
- Electrical power consumption efficiency of the amplifier cavity > 80%
The typical working tetrode values for 10KW output power in antenna are:
- Anode voltage = 10700V
- Anode current = 3.10A
- Control grid current G1 = 50-150mA
- Screen grid current G2 = 150-200mA
- Driver power = 900W
When the transmitter is tuned to work correctly at 10KW of output power in antenna, the
final amplifier doesn't present good working parameters if it works at low power.
Note that in this configuration the transmitter cannot work absolutely for long periods with
output power in antenna less than 7KW because the value of thermal power dissipation will
be greater than maximum value admissible for tetrode anode.
The reflected power value too read on the driver meter is never minimum when the
transmitter doesn't work at maximum output power for which is been setted.
2.3 TUBE
This power amplifier uses mainly the 4CX12000A tube.
The 4CX12000A ia a ceramic/metal power tetrode intended for use as a VHF power
amplifier. It features a type of internal mechanical structure which results in high RF
operating efficiency. Low RF losses in this
structure permit operation at full ratings to 110MHz.
The 4CX12000A provides high gain in FM broadcast service, and is also recommended for
RF linear power amplifier service. The anode is rated for 20Kw of dissipation with forced-
air cooling and incorporates a highly efficient cooler of new design.
It is also recommended for use as a grounded grid FM amplifier. In addition, grounded-grid
operation is attractive since a power gain as high as twenty times can be obtained.
2.4 R.F.
CAVITY
The R.F. Cavity is accessible when are been removed the fixed screws of the front panel.
It's divide in three sections: the top section in which is placed the motorizzations of the
tunings; the central section in which is fixed the tube and the bottom section in which is
placed the tube socket.
A temperature probe is placed externaly on the air chimney that is placed on the top of the
R.F. cavity. The protection circuit that continuously monitors this probe, switch of the
amplifier in case of overtemperature.
This section of the chamber is mounted on four motorized bars and can go up and down in
according to desired transmission frequency.
In the central section of the chamber, around the tube's socket, is situated a collar with
fingers to ground the control grid.
