A600 PA peak
reading meter PCB.
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One PCB for six peak reading
moving coil meter interfaces.
Read all info carefully before installing components into the PCB.
Meter PCB adjusted components value table.
With the here recommended fixed value resistor combinations, calibrated meter indications are achieved for 1mA moving coil meters.
Six 20210505 85C1 1200DPI moving coil meter scales PDF.
Print in color on A4, in high quality, and picture scale 100%
PDF parts list 20210502-33.
PDF TOP silk with updated component numbering 20210522.
The new drive meter range is 5Wp, and its alarm level is 4Wp.
My modified PA needs around 1Wp input for 400Wp output.
GATE DRIVE VOLTAGES of 16Vpp (about 4W input) or higher can blow the FET gates !
safest drive method :
Always use the max. output from the transmitter (me : Hermes Lite2 4W).
Use an internal attenuator (here 6dB) inside the PA, which is connected between the PA back panel and the input of the PA PCB.
Lower the PA drive with it to what is needed for 400Wp output (here 1W).
Circuits test and calibration with DC input test voltages.
The most easy way to assemble and achieve calibrated metering circuits, with still the possibility to correct meter readings for small signaling differences, is installing pre-adjusted trimpots. You should pre-adjust thes "GAIN" and "ALARM" and "FSD" trimmers, BEFORE inserting them into the PCB. See for the NOMINAL values in columns "GAINx" and "ALARMx" in the PDF table. FSD40 is a resistor of 270 Ohms. All other FSD resistors are 3k035.
After finishing the PCB :
Connect all meters and LEDs.
Place jumper PAgnd.
The PCB is now temporarily connected to the PA cabinet.
Temporarily set a CABgnd jumper on the PCB to connect the meter PCB to CABgnd.
Then disconnect the flat cable from meter PCB J5.
REM "x" is the PCB part number prefix.
In circuit 1 "x" is empty.
In circuit 2 to 6 "x" is 20 to 60.
Example : In circuit4 is D5 numbered as (Dx5) or D45.
REM : all meter circuits 1-5 (when having no input connected) will show burning LEDS. This is normal.
1. Connect a (low impedance) test voltage source (5Vdc max. "+"
to the appropriate input pin at J5,
and "-" cabinet ground).
2. Connect the 12Vdc power (max 18Vdc).
3. Set the test voltage to full meter scale deflection (see metering table).
4. Connect a digital DC voltage meter to Dx5 k (cathode).
5. The voltage should be 5.0Vdc (adjust with "GAINx").
PCBcircuit4 (reflected power) should indicate 2.23Vdc.
6. Check the moving coil full meter deflection (adjust with "FSDx").
7. Set the input voltage to the alarm level (see metering table).
8. The alarm LED should just light-up (adjust "Alarmx").
Together wit a burning LED, a buzzer can sound.
Go on with the next meter circuit.
Measure the PCB temperature with an infrared thermometer and compare it with the meter indication.
When the calibration is finished, remove the jumper "CABgnd", and re-connect the flat cable between meter PCB and PA PCB. The "PAgnd" jumper should be placed.
To prevent a ground loop, only the "+" of the 12V supply should be connected to the metering PCB. The 12V "-" should not be connected but is connected to the PA PCB with the J5 flat cable.
After connecting the PCB with the
meters and with the PA in mode standby :
a. adjust the mechanical zero screw of the power current meter for zero indication.
b. adjust the mechanical zero screw of the PCB temperature meter to the actual room temperature.
Transmit a 300W carrier until the moving coil meter indicates 50C. Compare with the PCB temperature near Q1 (MRF500AN) measuring it with an infra red meter.
Why peak meters.
Power Amplifier units not only can be damaged
by continues overdrive, but also by very short peaks.
To indicate dangerous levels, PEAK powers / voltages / currents indicators should be used, not mean value indicators.
The amplifier circuits on this PCB have therefore fast attacks, and slow decays.
Speech and continues tones should give (with equal drive) about the same meter indications.
This single PCB allows reliable connections with JST XH plugs to six moving coil meters, LEDs, buzzer and 12Vdc power. Placing nine jumpers to allow a buzzer to sound, and to choose grounding location. The six meter buffer circuits 1 to 6 are identical, with some identical component values. All to be connected moving coil meters are cheap 1mA 85C1 type (Aliexpress). This PCB is connected with only one 12 wide flat cable to the 2x6 pin signal output bus J5 at the PA PCB, and to a +12V supply. Meter indication and alarm levels are adjustable by trim pots, or readily calibrated by installing recommended resistor combinations.
Please excuse me : Due to a software problem in the
by me used old FREEPCB design software, not all component references are printed on
But identifying components is easy : When i added a new circuit copy of circuit1, all references were simply updated by adding 10 more to the references of the added circuit.
All lowest component references in circuit1 are numbered starting at " 1" ( R1, C1 etc.).
All lowest component references in circuit2 are numbered starting at "21" (R21, C21 etc.).
All lowest component references in circuit3 are numbered starting at "31" (R31, C31 etc.).
and so on.
The 5Vdc circuit component references are numbered starting at 70.
See the picture above.
Except the trimmers, most components with the same last reference cyfer in circuits 1 to 6 have the same values.
The column "Remarks" in the parts list gives some indications where components are available.
Conrad orderNrs are given as reference for component properties. You can order at Conrad.com (only in EU, order for more than 50 Euro for free postage). Or order equivalent components elsewhere. Then look at Conrad.com what the exact component properties are.
Download the PDF TOPsilk. At the PCB missing component numbering is completed on the PDF. Print it when installing components.
This component soldering is time consuming and focused work. More than 130 parts must be installed.
Not everyone can handle 1x2mm or smaller SMD components. Al components are therefore wired.
To save space, nearly all components are placed vertically. All resistors are 1/4W metal film 1% or better.
Connect the solder iron tip electrically to the mass surfaces of the PCB to prevent static damages. Handle the ICs with care.
Pay attention to the :
- Correct "trimmer" holes, if fixed resistors are installed in stead of trimmers. Three of the four holes are interconnected.
- Polarity of diodes. Stripe on the diode body = cathode, on the PCB marked as "k". Diode anode is on the PCB marked as "a".
- Polarity of electrolytic capacitors. The longest wire is + (positive).
- The notch at IC sockets, at the PCB, and at the ICs (pin1).
The downloadable PDF table and PDF list give values for replacing the trimmers by fixed resistors.
Afterwards fault search is time consuming. To prevent placement faults and malfunction, i suggest to work as follows :
First place and solder components all of one same value.
Example : Place solder all 2k2 resistors R1, R21, R31, R41, R51, R61.
CHECK your solder work !
After that, place components of one other same value.
Example : Place and solder all 10k resistors R2, R22, R32, R42, R52, R6.
Solder component types in the following order:
- IC sockets. See the notch at one small socket side and on the PCB.
- Ceramic capacitors.
- Diodes (See "k" = cathode, the side with the ring on it, "a" = anode).
- Resistors. R47 is not installed.
=> In the drive power circuit a 22k resistor (R67, not printed at the PCB) must be soldered parallel at its input (at the PCB bottom parallel to D61).
Before soldering fixed resistor pairs in stead of trimmers GAIN, FSD and ALARM :
MEASURE the total value of the pair with a digital ohmmeter. It must be within 1% of the nominal value in the metering table.
FSD40 is a resistor of 270 Ohms. All other FSD resistors are 3k035.
- Jumper pins.
- JST XH busses.
- Trimpots. You should pre-adjust the trimmers to nominal values, BEFORE inserting them into the PCB. See PDF table.
- Elcos. 6mm elcos JUST fit between other components. Do not use thicker types.
- Insert the ICs. See the notch at one small side. Handle the ICs with anti-static care.