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Cathode resistor Rc creates DC and RF negative feedback, thus stabilizing the gain and equalizing the
frequency response. The varistor VSsg in the screen grid circuit protects the tube screen grid, and
voltage regulator in the events of a flashover.
The combination Lp1-Rp1 in the plate circuit is a VHF/UHF parasitic suppressor. DC plate voltage is fed
through chokes RFC1-RFC2 and the capacitor Cb3 blocks it from the output. The output circuit
comprises LP1, LP2, LL, CP1-CP3, and CL1-CL3 which form a classic Pi-L network and suppress the
harmonic frequency emissions. This tank is switched and tuned over the bands by S1A-S1C and the air
variable capacitors CP1, 2 and CL1, 2. The output signal is fed through an additional VHF low-pass filter
for frequencies above 55MHz (Lf1, Lf2 and Cf). Then it is passed through the vacuum antenna relay K1,
wattmeter current transformer TA1, and a high-pass filter RFC4-Ca for frequencies below 100kHz, to
the antenna output. The chokes RFC3 and RFC4 keep track of the antenna relay contact conditions and
together with Ca prevent the plate supply from reaching the antenna. RFC4 shunts it to ground if the
DC blocking capacitor Cb3 fails. The resistor Ra protects the amplifier from charging Electro-static
energy fed by the antenna.
The PLATE CAPACITIVE DIVIDER and RF WATTMETER are the main sources of information for the
control circuit of the amplifier during the antenna impedance matching process. The control circuit is
based on the 80C552 micro-controller from Philips.
All voltages are delivered from the MAINS&LOW VOLTAGE and HIGH VOLTAGE SUPPLY PCBs. The
control grid, screen grid and plate currents, plate cooling airflow temperature, reflected power etc. are
permanently monitored. Many software-derived protections are based on this information.
* Detailed electrical schematic diagrams are available from ACOM or from your dealer on request.
6-5. Troubleshooting
See S.5-3 for the method of reading the auto-protection signatures. You can decode them using the
information below. *
The signatures are structured in two lines, three groups by six symbols for every one event of
auto-protection. The last event is numbered as 1A-1B pair of lines, and the oldest one is 7A-7B.
The meaning of the first group is as follows:
a) nA - the number of the trip;
b) Next three symbols mean the following:
PN0 - tests made during Power-On procedure, before HV is ON;
PN2 - tests made during Power-On procedure, after HV is ON and 1 second after step-start is
closed;
SB0 - tests made in Stand-By, during the warm-up period or while entering Stand By (from Operate);
SB2 - tests made during Stand-By, after the warm-up period;
PR0 - tests made while entering Operate;
PR2 - tests made during Operate;
TR0 - antenna relay tests made while changing from Tx to Rx (during Operate)
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