Step 9
– With your multimeter on the 500 volt DC range,
carefully connect the meter's black lead to chassis ground and
the red lead to the positive end of C6 (B+). The voltage here
should be something close to +470 +/- 15 volts (photo 8.1a). The voltage at this point will be
20V lower when the power tubes have been installed.
Step 10
– Remove AC power by disconnecting the AC power cord from the AC source.
Step 11
– Install the preamp tube.
Step 12
– Plug the amplifier's AC
power cord into the AC power
source at the wall.
Step 13
- The panel indicator should
illuminate. Monitor for any unusual
smoke or smells or blown fuse.
If anything unusual occurs,
disconnect power immediately and
review connections.
Step 14
– Let the amplifier warm up for 2 minutes. With a multimeter on the 20 volt range,
carefully connect the meter's black lead to chassis ground and the red lead to the positive
side of C3. If C3 is not installed, the red lead can be connected to pad “n” instead. The
voltage here should be close to +1.8 +/- 0.5 volts (photo 8.1b).
Step 15
– Move the red lead to the positive side R7 (pad “g”).
The voltage here should be close to +1.8 +/- .5 volts.
Step 16
– If these measurements are correct, remove the AC
power by disconnecting the AC power cord from the AC source.
Step 17
– Install the power tube.
Step 18
– Connect speaker to output jack.
Step 19
– Turn volume to minimum position, leaving the
amplifier power switch to “on”.
Step 20
– Plug the amplifier's AC power cord into the AC power
source at the wall.
Step 21
– The panel indicator should illuminate. Monitor for any unusual smoke or smells or
blown fuse. If anything unusual occurs, disconnect power immediately and review
connections.
Step 22
– Let the amplifier warm for 2 minutes.
With a multimeter on the 200 volt range, carefully connect the meter's black lead to chassis
ground and the red lead to the positive side of C4. The voltage here should read close to +22
+/- 3 volts (photo 8.1c).
Whenever testing voltages, it is recommended to keep your free hand off of the chassis. In
this way, there isn't a path for significant current to flow through the body to ground in case
the measuring hand accidentally comes in contact with high voltages.
WARNING
These voltages are being measured without tubes installed. These values will decrease with
the added load of the tubes bringing the voltages within acceptable tolerances of the caps.
NOTE
photo 8.1a
photo 8.1b
The presence of voltages at steps 14 & 15 indicates that both halves of V1 are correctly
sourcing current.
NOTE
photo 8.1c
The presence of voltage at step 22 indicates that V2 is correctly sourcing current.
NOTE
TubeDepot.com 21
