Voltage Check
Once you have completed the resistance check of the circuit the next step is to perform a
voltage check of the circuit. This will help to assure that parts have been connected to the
proper terminals and soldered properly before you connect a source and headphones to the
circuit.
( ) Turn the volume control all the way down.
( )Install the 12AU7 and 6080/6AS7 tubes in their sockets.
( ) Clip the fuse into the fuse cover and insert the cover into the power entry module.
( ) Plug the IEC power cord into the power entry module. Do not plug the cord into the wall yet.
( ) Turn the chassis over and attach the negative lead (typically black) of a volt-ohm meter to
ground. A good spot to do so is at terminal 12. Use of a clip lead to connect the black test lead
to the ground will free one hand, making testing much easier and safer. Switch the meter to read
DC volts on the 400V or higher scale.
( ) Plug in the amplifier and turn on the power switch. If the tube filaments do not glow after a
few seconds, power down and check the fuse. If it is blown, recheck your wiring one more time.
Correct mis-wires, replace the fuse and try again.
( ) If the tube filaments glow properly, wait at least thirty seconds and then CAREFULLY
measure voltages using the positive lead (typically red) of the volt-ohm meter at the following
terminals:
WHOA! SAFETY CHECK!
ALWAYS USE EXTREME CAUTION WHEN MAKING VOLTAGE MEASUREMENTS ON A LIVE
PIECE OF ELECTRONIC GEAR.
Always wear rubber soled shoes when working on electronic gear, particularly if you are working
on a concrete floor. Don’t work in socks or bare feet. A circuit can be created from the live
preamplifier to ground through your feet.
NEVER, REPEAT, NEVER TOUCH THE LIVE AMPLIFIER WITH BOTH HANDS WHEN
TESTING. IF YOU CREATE A CLOSED CIRCUIT THROUGH YOUR HANDS AND ARMS, THE
VOLTAGE AND CURRENT CAN STOP YOUR HEART. The old timers would keep one hand in
their pocket when working with live gear to avoid a fatal slip up. Also, it is a bit safer to use your
right hand than your left to touch the chassis, as any current passing through your hand to the
ground would be less likely to pass through your heart. The following voltages have been made
with an AC mains voltage of 119VAC:
Terminal Voltage (VDC unless otherwise specified)
1 75-90
2 170
3 0
4 170
5 75-90
6 0
7 100
8 0
9 100
10 0
11 0
12 0
13 170
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