Mableaudio 5E3, Инструкция по сборке, Страница: 37 / 39

Initial testing:
Install the knobs and fuse, but don’t install the tubes at this time . Put the standby switch in standby mode, the
power switch off, and both volume knobs all the way down.
Now, with the amp sitting on your workbench wiring side up, plug in the power cord and turn the power switch on.
The pilot light should turn on at this point. If it doesn’t, turn the amp off, unplug it, and check your wiring again.
Check to see if the fuse is blown. If it is, there is a short somewhere in your wiring, or the AC line to the power
switch is miswired. Don’t proceed to the next step until the problem is fixed.
Set your multimeter to the 20V AC range (or any AC range that will read voltages below 10V) and test the filament
wires to each tube socket. Check to see that there is 6.3VAC between pins 2 and 7 on each 6V6/6P6 socket, and
between pins 4/5 and 9 on each preamp socket. Check to see that there is 5VAC between pins 2 and 8 of the
5AR4 power tube socket.
Note: Without the tubes installed, these voltages will run high. It is not unusual to see 6.8VAC on the 6.3v lines
and 5.6VAC on the 5V line.
If these voltages are half or double what they should be, you may have the wrong power transformer for
your AC line current. Contact the seller for the correct transformer. Do not proceed until you have the
correct voltages.
With the negative (black) lead of your multimeter attached to the chassis ground, flip the standby switch to turn on
the high voltage supply. Set your multimeter to the 500V AC range or higher, and check the voltage at Pin 3 of the
rectifier tube socket, and then at Pin 5. Both voltages should be around 355VAC. If you are using a 5Y3 rectifier
without the diodes, do this test at pins 4 and 6 instead. There is no need to discharge the capacitors at this point
without the rectifier tube in place.
Turn the power off and install the rectifier tube. Make sure the key on the middle of the base of the tube matches
up with the notch in the socket. You may need a helper to push down the “wings” of the tube retainer while you
carefully press the tube firmly into place.
With the standby switch in standby mode, turn the main power switch on. The rectifier tube should glow. Give it
a couple of minutes to warm up and flip the standby switch to turn on the high voltage.
First, let’s measure the positive side of each big capacitor. Set your meter to the 500V DC range or higher. You
should get high voltage (400+ volts) at the positive end of each capacitor. Each voltage will be different.
From now on, we will be working with high voltages. Observe the following cautions:
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Connect the negative (black) lead of your multimeter to the grounded chassis, and measure
all voltages in reference to ground with the red lead.
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Follow the “one hand” rule when testing. Only one hand should be in the chassis at a time.
Keep your other hand in your pocket.
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Wear a heavy long sleeve shirt or jacket without any metal buttons on the sleeves.
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When you power off the amp to do work, unplug the amp from the wall and discharge the
big capacitors (22uf 450v) first. Use a pair of pliers to hold a 10K (or thereabouts) resistor
between the positive side of the middle capacitor (where the red wire connects) and the
chassis ground for about 5 seconds. Use your multimeter to see that the voltages on the
positive ends of each capacitor have dropped to a safe level.