Acom 1011 Manual de instruções - Página 16

Procurar online ou descarregar pdf Manual de instruções para Amplificador linear Acom 1011. Acom 1011 19 páginas. Hf linear amplifier

The two primary line (mains) fuses in the amplifier are located on the rear panel (Fig. 2-1). They are of

the fast (quick blow) type, European size 5 x 20 mm. Use 10 A for 100-120 V ac operation; 6.3 A for

200-240 V ac operation. Suitable types are:

For 120 V: 10 A 250 V 5 x 20 mm fast (quick blow), LITTELFUSE 0217010; Wickmann 1942100000

For 240 V: 6.3 A 250 V 5 x 20 mm fast (quick blow), LITTELFUSE 021706.3; Wickmann 1931630000

Besides the primary fuses, there are also fuses located on the HV PCB and on the MAINS PCB (inside

the amplifier). They are European size 5 x 20 mm, 0.8 A, 2 A and 5 A, time lag (slow-blow) type.

Suitable types are:

HV PCB: 2 A 250 V SLOW BLOW (Time Lag) 5 x 20 mm; LITTELFUSE 0218002; Wickmann

1951200000

MAINS PCB: 5 A 250 V SLOW BLOW (Time Lag) 5 x 20 mm; LITTELFUSE 0218005; Wickmann

1951500000

MAINS PCB: 0.8 A 250 V SLOW BLOW (Time Lag) 5 x 20 mm; BUSSMANN type S504-800mA

These latter fuses must not be replaced by the user. Replacing these internal fuses is potentially dangerous

and must be done only by a trained service technician. Contact your ACOM dealer for assistance.

5-3. Tubes Replacement

Two 4CX250B (7203) ceramic-metal tetrodes are used in the amplifier. The new tubes must be supplied

as a Matched Pair with close electrical characteristics. Replacement is a complex and potentially dangerous

operation that involves adjustment of the plate idling current. This should not be attempted by the user.

Contact your ACOM dealer.

See Fig. 5-1 ACOM1011 Simplified* Schematic Diagram. The two 4CX250B (7203) ceramic-metal

tetrodes (V1 and V2) with a total plate dissipation of 500W (forced air cooling) are grid-driven. The input

signal from the RF INPUT jack is passed through a broadband input matching circuit, which consists

of components on the INPUT PCB and includes the drive-power swamping resistor Rsw. This circuit

tunes out the input capacitance of the tubes. The swamping resistor Rsw is a termination load for the

matching circuit and can dissipate up to 80 W of RF drive power. It also eliminates any tendency toward

oscillation by the tubes, ensuring excellent RF stability of the amplifier.

The cathode resistors Rc1 and Rc2 create DC and RF negative feedback, thus stabilizing gain and equalizing

frequency response. The combinations Lp1-Rp1 and Lp2-Rp2 in the plate circuits are VHF/UHF parasitic

suppressors. DC plate voltage is fed through chokes RFC1-RFC2 and the capacitor Cb3 blocks it from

the output. The output tank, comprised of LP1, LP2, LL, CP1-CP3, and CL1-CL4 , forms a classic Pi-L

network and suppress harmonic frequency emissions. This circuit is switched and tuned by S1A-S1C

and the air variable capacitors CP1, 2 and CL1, 2. The output signal is fed through the antenna relays K1

and K2 in the WATTMETER PCB. The WATTMETER PCB also includes a high-pass filter for frequencies

below 100 kHz, and it prevents the plate supply from reaching the antenna.

The plate RF voltage is monitored through the capacitor Ca and together with the RF WATTMETER is

the main source of information for the control circuit of the amplifier in evaluating tuning quality. The

control circuit is based on the ATMEGA-8L micro-controller from Atmel. All voltages are delivered

from the line (MAINS) and HV PCBs. The currents of the control grids, screen grids, and the plates, as