ACOM 2000A


ACOM 2000 schematic.pdf
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Регулировка и проверка защиты

1. DRIVE LED blinks above 80W; trips above 126W. Nominal value is 50...60W for rated output. Reduce drive to overcome the protection.


2(a). FWD-P and RFL-P trip above 203W during standby. Bypassing up to 200W forward and reflected power through the amplifier in STBY and OFF mode is safe. A warning is issued in STBY at 203W threshold to secure amplifier's bypass circuitry safety. With 200W-transceivers you may overcome an eventual warning by reducing the power of about 5-10% or so, when the 203 watt threshold is exceeded accidentally.
Please note, that switching off the amplifier does not resolve the problem,as the amp. only could not tell you that the power is too high for it's bypassing relay, and a risk of damage still exists with more than 200W. If you need more power with the amp. off, you should reconnect the input and output cables leading to the amplifier in order to take it out of any transmitting path for more than 200W.
2(b). RFL-P trips above 502W during operate. Typically a no-load condition or misselected antenna after a band change is the cause.


3. IP LED: blinks above 1.4A plate current; time-lagged trip at 1,6A for 4 seconds; instanteous trip above 2.4A . Reduce drive to overcome it. Nominal current is 0,95...1,25A, and may vary slightly depending on mains voltage, band, and tuning quality. Idling current is set in the factory to 50mA / 375mA (when keyed with no RF / small RF applied), for minimum IMD.


4. IG2: nominal value of the screen grid current is 60...80mA, but it widely varies with mains, tuning quality, and different tubes. A range of 0...100mA is acceptable. Protected by hardware at 120mA, and by software at 200mA for 20ms time lagged. Reduce drive to overcome it.

5. IG1: nominal control grid current is 5...10mA, trips at 20mA for 20ms time lagged. Reduce drive to overcome it.
The ALC signal is grid-current derived. When the control grid (G1) current appears during transmission between zero and 5mA (both tubes summary), the ALC voltage is zero. When this threshold is exceeded, a negative voltage appears on the ALC output, which is linearily proportional to the amount of grid current above the 5mA threshold. Its maximum value (-11V) is reached around 15mA grid current, and can be continuously reduced to zero via the ALC regulator. The regulator is located on the rear panel, just above the ALC connector. Clockwise rotation will increase the maximum ALC voltage (and the loop gain of the system "amplifier + transceiver"). Using this output is normaly not needed with modern transceivers.
The electrical parameters of the ALC output are as follows:
- maximum output voltage (negative to ground) up to -11V;
- output resistance about 500 Ohms;
- maximum output current up to -10mA (self-protected).


6. Concerning the "HEATER" LED indicator you may need the following information:
If "HEATER" indicator lits continuously, probably mains voltage is lower than the nominal; if it often blinks, mains voltage is higher. You may still work safely even when "HEATER" is lit, as this is a warning indication only, but the protection threshold is yet close. If even more severe mains voltage deviation occures, the auto protection would trip, the red "PROT" LED will flash, and an appropriate text message will be issued on the LCD.
In order to determine how close are the trip conditions, you may enter the MEASURE sub-menu and monitor the following values:
- MAINS (line input voltage, no protection is directly derived);
- FIL-V (filament voltage, 10V to 14.4V is acceptable);
- IF-REAR (filament current - rear tube, 3A to 4.4A is acceptable);
- IF-FRONT (filament current - front tube, 3A to 4.4A is acceptable);
The heater voltage protection would trip at voltages below 10V or over 14.4V, and the corresponding message to the operator is issued on the RCU.
Respectively, the thresholds for heater current protection are 3A and 4.4A, and appropriate messages appear when tripped. For your information, the nominal filament voltage is 12.6V, and the nominal current is 3.6A. The "HEATER" indicator on the RCU is normally dark. It will constantly light if the filament voltage drops below 11.6V, and it will frequently blink if the voltage exceeds 13.6V (in order to inform you that nearly half of the acceptable range is crossed). In both cases the voltage selection may need to be changed if this conditions predominate. See also p.11 below.


7. Exhaust air Temperature. The optional external fan (when mounted) is accelerated at 90deg.C., and is slowed after the exaust air temperature drops below 80deg.C. Full temperature scale on the RCU (up to 130deg.C., 10 degrees per bar) is acceptable. A ">" sign appears when the scale is overflowed, and a protection trips at 150deg.C threshold.
If the temperature is higher than 80deg.C. at the moment you switch the amplifier off, the tubes are instantly powered off, but the blower would continue cooling, until the exhaust air temperature drops below 80deg.C.

Another protection system monitors the air motion in the tube deck volume. This would prevent the control system of being let down, while measuring a low-temperature but still-standing air above hot tubes. You may get a "LOW AIRFLOW" message in such conditions. Check whether the inlet / outlet cutouts of the amplifier chassis are not accidentally covered by alien subjects, and let the tubes cool. Clean or replace the air filter. Add the optional external fan in severe temperature conditions, and for continuous modes of operation.


8. DC supply voltages:
template --- "nominal: +/- tollerance% (protection thresholds)"; 
+5V: +10/-15% (4.25...5.5)V; logic and analogue circuits voltage.
+/-12V: +15/-15% (10...14)V; analogue and RS232-port voltage.
+24V: +27/-30% (17...30.5)V; power-on relays voltage.
+48V: +27/-30% (34...61)V; antenna and input relays voltage.
+12/340V controlled screen grid voltage. Typically 10...15V during standby (EG2 is off), and 320...350V during operate (EG2 is on). Protection thresholds: more than 40V during standby; less than 150V or more than 430V during operate.
+2850V plate voltage (no load condition): +15/-55% (1280...3300)V; 2300...2500V is nominal at various loads and mains internal resistance for rated output.
-124/-75/-52V controlled bias voltage. Typically -115...-130V during standby / -70...-80V during operate idling / -45...-60V during operate with RF applied. Adjusted in the factory during setting of plate idling currents for minimum IMD (see p.3 above). Protection thresholds: less than -100V during STBY, and less than -35V during OPERATE.


9. The following measurands are calculated on the base of directly measured parameters:
- DC INPUT is calculated from (HV x IP); no protections from DC INPUTare derived.
- GAIN is calculated from (FWD_P / DRIVE); a "LOW GAIN" protection is derived at a threshold below 10dB gain.
- VSWR is calculated from Gm=(RFL_P/FWD_P); VSWR = (1 + Gm) / (1 - Gm); no protections derived.
The used above HV, IP, DRIVE, FWD-P, RFL-P, the 12 remaining measurands listed in S.4-3, p.19 of the Operating Manual, and also 4 supply voltages
are directly measured via the analog-to digital converter in the CPU PCB. Multiple protections and tuning criteria are based on this information.


10. In addition of the above listed, a variety of values are checked dynamically while the amplifier's status is being changed, thus more protections may trip if bad conditions are detected. For instance, the heater current peak, HV, and EG2 are differently controlled during the power-on period, or while changing from standby to operate and vice versa. Also, the input and output relays contact time performance is verified at every dot/dash keying, and RF appearance.


11. Mains voltage tollerances.
See S.7-1j on p.29 of the Operating Manual. Normally, a +/-10% excursion of nominal tap voltage is acceptable. For instance, this is 216...264V with 240V nominal. The amplifier would work up to +/-15%.
If you however exceed this threshold (below 204V or over 276V for 240V nominal), supply voltages and/or currents may reach dangerous values. No protection is directly associated with the mains voltage, but nearly all supply voltages (and some currents) would reach threshold values, so various amplifier protections would begin tripping, in order not to let any damage in both: power supply, or the tubes.
Anyway, the control circuit is happy even at a voltage drop of-20%, i.e. below 190V, with 240V nominal tap selected. If mains voltage still drops further (below -25%), the control circuit in the RCU immediately switches off the amplifier, and becomes inoperative until the voltage restores to at least -15...20% of nominal, i.e. at least 190...200V, with 240V nominal. This hysteresis is intended to reject unusable RCU restartings if the voltage is continuously fluctuating near the lower limit. 
A controllable step-up / step-down tap-transformer (for 20A nominal current) would be a good solution in such conditions, not only for the amplifier. You may find also suitable automatic AC voltage regulators on the market.


12. An additional possibility is foreseen in order to partly compensate for any mains voltage deviation not to affect the tubes plate efficiency. This is the DEF sub-menu in the OFF menu (see also page 22, 5-6a of the Operating Manual). Set the MAINS VOLTAGE menu selection to HIGH, when mains voltage is typically 5% (or more) higher than nominal tap (i.e. higher than 252V with 240V nominal). Set the menu selection to LOW when mains voltage is typically 5% lower than nominal tap (i.e. lower than 228V with 240V nominal). For lower voltages first set lower nominal taps of the transformer (i.e.220V, 200, 120 or 100V), and observe same rules about menu voltage selection. Anyway, a voltage of (230...240)V should be considered to be NORMAL with 240V nominal tap.
Please note, that this menu selection does not change the real supply voltages, but only the plate load resistance to which the AUTO TUNE procedure would match your antennas. With HIGH selection you will request a higher plate resistance, and vice versa, thus merely doing the best at your real conditions.

Использование ALC

Information provided by Vasco, LZ1JK

Using ALC feedback from the amplifier to the transceiver, in order to limit the PEP drive, sometimes results in a potentially unstable system, which may tend to generate relaxations. This depends on the resulting loop gain and timing parameters, that is why a careful adjustment is needed to make it useful.
Anyway, as you decided to use the ALC system, here are the amplifier's ALC output electrical specifications of ACOM2000A :
- maximum output voltage (negative to ground) up to -11V;
- output resistance about 500 Ohms;
- maximum output current up to -10mA (self-protected).
The ALC signal is grid-current derived. When the control grid (G1) current changes between zero and 5mA (both tubes summary), the ALC voltage is zero.
When this threshold is exceeded, a negative voltage appears on the ALC output, which is proportional to the amount of grid current above the 5mA threshold. Its maximum value (-11V) is reached around 15mA grid current, and can be reduced to zero via the ALC regulator. The regulator is located on the rear panel, just above the ALC connector. Clockwise rotation will increase the maximum ALC voltage, and the loop gain of the system "amplifier + transceiver".

 What I could suggest is to reduce the maximum voltage generated by ACOM2000A, in order not to exceed the maximum permissible voltage for your transceiver.For this purpose connect a voltmeter to the ALC output and enter the MEASURE submenu "I-GRID". Increase drive power until you reach 17-18mA grid current. Do not exceed 20mA as a protection would trip there. At this point you will have the maximum ALC output voltage from ACOM2000A, so reduce it until it becomes safe for your transceiver's ALC input (check in your transceiver's operating manual for the proper voltage value).
After having a safe ALC voltage, connect it to the transceiver's ALC input. Then try to adjust it in order to yeld a good regulated "amplifier + transceiver" system, but using ONLY LESS positions of the ACOM2000A ALC output regulator.

Интерфейсы усилителя

1. The amplifier's T/R-control input for the antenna relay is called "KEY-IN". When in OPERATE mode, on this input appears a DC signal that is to be held low to activate the amplifier to the transmit mode. This can be done via either a relay contact or a semiconductor (transistor or integrated circuit) with suitable polarity (plus to the ground).
NOTE: You should prefer a semiconductor output when it is available on your transceiver, since relay contacts on some models are slow with respect to their RF output. You may see a "Hot-Switching Warning" or "RF detected at wrong time" message otherwise. This message means that an eventual hot switching has been prevented by the amplifier's protection system. You should change to the semiconductor output in such conditions. In addition, utilizing the semiconductor output, you may disable the transceiver's relay clicking (on some models there is a switch intended for a case when the relay is not needed).
The electrical specifications of the amplifier's KEY-IN input are as follows:
- Switching voltage (open circuit): 15V max (12V typ.), plus to the ground;
- Closed-circuit current: 15mA max;
- Voltage drop / resistance of the control output @ 15mA (closed circuit): 1.5V/250 Ohm max.
You can control the KEY-IN signal in two different methods. Look at (3) for a second way.  For the preferred mode, you have to connect the KEY-IN socket to the transceiver's output that goes to the ground when you transmit. Practically all transceivers have such an output, and their electrical specifications exceed the amplifier's requirements. Transceivers producers give different names to this output, and they are for instance: TX-GND, SEND, *T/R-LINE, KEY-OUT, etc.
Some transceivers require that their signal "ground on transmit" be implemented via a software command, or by changing of a switch on the rear panel, or interior of the transceiver. Some models generate a "+12V on TX" signal. Then, you may need a simple n-p-n or n-mos transistor, controlled through a 10kOhm resistor to the base or gate, in order to "invert" the available signal in a "GND on TX". Look in your transceiver's manual or contact your dealer or ACOM directly for details about a particular model. Please use always shielded cables for these connections.
2. The KEY-OUT socket on the rear panel is a "phono" type (RCA) connector. When you don't use the second method of the connection (see p.3), this is an extra output signal from the amplifier, that could be either used or not. When used, it would improve the T/R process of switching and would increase the exploitation reliability.
The KEY-OUT output is usable when the transceiver has available a respective input to disable transmitting when the amplifier may need it. If your transceiver has no such input (for instance ICOM models), or you use the second way of the KEY-IN connection (p.3), please don't worry: the amplifier will be fully protected and will function normally, so the KEY-OUT may remain unused.
If your transceiver however possesses a suitable input that is capable to disable transmission, we recommend that you utilize that feature. Just connect this input of the transceiver to the KEY-OUT socket of the amplifier. Transceiver producers give different names to this input, and they are for instance: TX-INHIBIT, MUTE, LINEAR, KEY-IN, etc. It is available sometimes on BAND-DATA, ACC, EXT, LIN, ATU, and etc rear-panel connectors. Some transceivers may require that a "transmit disable" function is implemented via a software command, or by changing of a switch, or via adding an external pull-up resistor, etc. Look in your transceiver's manual. You have to use the preferred connection of the KEY-IN socket (p.1) to utilize this feature.
The output KEY-OUT of the amplifier is an open-drain circuit and it can hold a positive DC signal to the ground. During all the periods when the amplifier is ready to transmit, this line will always pattern the requests "GND on TX" in order to enable transmission. When transmitting is not permissible, the output becomes open (for instance, while the antenna relay is in process of switching-over) and the transceiver would stop RF driving.
The electrical specifications and timing of the amplifier's KEY-OUT output are as follows:
- Switching voltage (open circuit) - up to +50V,
- Switching current (closed circuit) - up to 20mA,
- Internal resistance @ 20mA (closed circuit) - 120 Ohm max,
- Delay time - 5ms max (2...3ms typically).
While the amplifier is not powered, and in STANDBY mode, this output is directly connected to the KEY-IN socket. Thus, the amplifier will send back the "ground on transmit" signal to the "TX enable"-input of the transceiver always during OFF and STBY modes in order not to disable any transmission.
In OPERATE mode the signal KEY-OUT will pattern the signal "ground on transmit" that is coming on the socket KEY-IN, always when the antenna relay is in safe position and when no other warning is present. The signal KEY-OUT will reject transmitting if the amplifier detects any risk condition.
Besides, the amplifier contains an independent self-protection that looks after the relay safety during a T/R-switching, regardless of taking or not an advantage of the KEY-OUT signal.
3. If your transceiver has not a suitable connector providing an output signal "ground on transmit" nor "+12V on transmit", you can use the second connection method as described below.
Connect the PTT or CW-keying contact to the amplifier's socket KEY-IN on the rear panel. Then connect the amplifier's socket KEY-OUT to the input PTT or CW-KEY of the transceiver. Always use shielded cables for these connections.
CAUTION: Please check up, that the parameters of the signals PTT and CW-key of the transceiver met the specifications of the "KEY-OUT" output of the amplifier (see p.2 above). Some very old transceivers models may require buffering if the requirement is higher than 50V/20mA.
With the second way of connection, the amplifier will just pass the PTT or keying signal directly to the transceiver always when powered off and during STBY mode. During OPERATE, the signal will pattern your PTT/keying after the antenna relay reaches a safe position, and will disable transmission during relay's motion as well as during any risk condition.
The second way of controlling the transmit/receive process could be very useful also if the transceiver has an incorrect timing sequence of its T/R signals. For instance, if the RF power appears before a "ground on transmit" is fed to the amplifier.

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