R.V.R. Electronica VJ3000, Maintenance Manual

Page: 20 / 50

R.V.R. ELETTRONICA S.r.l. (BO) Pag. 20
VJ3000 - Technical and Maintenance Manual
the protection system re-enables the unit unless the fault is still
present, in which case the cycle is repeated upto a maximum of 11 times,
after which the unit is shutdown indefinately.
At this point only manual or remote intervention can restart the unit.
If during 1 of the 11 attempts to restart it, the unit successfully
restarts and continues wirking for more than 30 minutes, the protection
cycle counter is reset to zero, while the number of cycles and the data
concerning the fault are stored in the memory.
2.5 TUBE
This power amplifier uses mainly the 3CX3000A tube.
The 3CX3000A high-mu forced-air power triode provides relatively high
power output as an amplifier, oscillator or modulator at low plate
voltage.
The tube has a low inductance cylindrical filament-stem structure which
readily becomes part of a linear filament tank circuit for VHF operation.
Operation with zero grid bias in many applications offers circuit
simplicity by eliminating the bias supply.
Grounded-grid operations is attractive since a power gain of over twenty
times can be obtained.
2.6 VOLTAGE STABILIZER (OPTIONAL)
This stabilizer is a single phase design fitted inside the unit with
connector blocks for the input eand output (Fig.15).
It comprises: a variac, AT; a series transformer, TS; a servo motor, S
and a control circuit, C. The stabilized output voltage, Vu is
continuously compared to a reference voltage and the difference between
the two is used by the control circuit to drive the servo motor which
rotates the variable autotransformer reducing the difference to zero.
In this way any difference between the output voltage of the stabilizer
and the reference voltage is immediately reduced to zero maintaining a
constant output voltage.
Please refer to Table I for the specification.
2.7 R.F. CHAMBER
The R.F. Chamber is accessible oce the rear panel has been opened,
by removing the fixing screws from the internal panel.
It is devided into three sections; the top section in which the motorized
tuning mechanism are situated; the central section in which the tube is
mounted and the bottom section where the tube socket is positioned.
A temperature sensor is fitted to the outlet of the air flue which is
fitted to the top section of the chamber.
The protection circuit which countnuously monitors this sensor, will shut
down the amplifier in the case of excess temperature.
This section of the chamber is mounted on four, motorized threaded rods
and can be moved up and down according to the desired transmission