Mableaudio 5E3, Инструкция по сборке, Страница: 38 / 39

Now, measure the voltage at each pin of the 6V6/6P6 tube sockets. You should get high voltage (400+ VDC) at
pins 1, 3, and 4 and 0VDC on pins 2, 5, 6, 7, and 8. Remember pins 2 and 7 carry 6.3VAC, but there should be no
DC on those pins. On the preamp tubes, you should get high voltage on pins 1 and 5, and 0v on the rest of the
pins.
If you get high voltage on pins that should be 0V, check your soldering for solder bridges on the tube sockets.
Final test:
Discharge the capacitors and Install the rest of the tubes. Remember to line up the key on the output tubes to the
notch in the tube socket. On the preamp tubes, there is a gap between pin 1 and pin 9 that needs to be lined up
between the tube and the socket. Leave the tube shields off for now. Connect an 8 ohm speaker to the jack
closest to the output tubes.
Start with the standby switch in standby mode. Turn on the main power and observe the tubes. They should
begin to glow. After the tubes warm up for a few minutes, flip the standby switch. With no instrument plugged in,
there should be almost no noise coming from the speaker. Turn the tone all the way up, and then turn each
volume control up and down and observe the noise level. No amp is 100% quiet, but if you did things right, you
should hear almost no noise or hum even with all three knobs turned all the way up.
Install tube shields on the preamp tubes, turn the volumes all the way down, and plug your guitar into one of the
input jacks. Turn the corresponding volume knob up and start playing. Test all four input jacks. Try each one
out at different volumes, and make sure the tone knob does what it should do.
Troubleshooting:
If you get no sound at all, there are still a few things to try. Concentrate on the output tubes and the output
transformer wiring. Make sure that the green and black wires are connected to the tip and ground tabs on the
output jacks respectively (Page 17). Go back to the output tube wiring on page 18 and check that you did
everything right.
Chopstick Test:
It is a fact that most American amp technicians eat Chinese food with a fork, but ask for chopsticks anyway. A
plain wood chopstick is a very useful diagnostic tool. Sure, you can use any non conductive stick like a pen,
pencil, or a wand from Hogwarts, but where’s the fun in that?
Put the amp chassis on your workbench wiring side up with a speaker connected. Turn it on and wait for the
tubes warm up. Turn the tone control all the way up, and both volumes at about ½ up (if you get a loud hum
already, you can turn the volume down so the noise doesn’t drive you crazy). Hold the chopstick vertical and tap
the end on each component and soldering joint. You may hear a very soft click from the speaker, which is normal.
When you hear a loud click, buzz, or hum, you’ve just found a bad component or solder joint!
This method works well for finding bad components on an older amp too.
To standby or not to standby:
In a cathode biased amp with a tube rectifier like the 5E3, it is not necessary to wait for the tubes to warm up before
taking it off standby. In fact, you can just leave it off standby unless you need to take a break from playing, so the
tubes are warm and ready to play immediately. However, if you are going to leave the amp for longer than ½ an
hour, you should shut it off. Leaving tubes hot for hours without high voltage will reduce their lifespan.