Step 4
– Let the amplifier warm up for 2 minutes. With the multimeter
on the 20 volt range, connect the meter's black lead to a chassis
ground point (photo 8.2a) and touch the red lead to turret T1. The
voltage here should be close to +1.4 (photo 8.3a).
Step 5
– Adjust the meter range to the 200 volt range and move the red
lead to turret T17. The voltage here should be close to 83 volts (photo
8.1d).
Step 6
– Adjust the meter range back to the 20 volt range and move the
red meter lead to turret T27. The voltage here should read 3.4 volts
(photo 8.3c).
Step 7
– Remove the AC power by disconnecting the AC power cord from the AC source.
Power Tubes, Installation and Testing
Step 1
– Install the two power tubes.
Step 2
– Connect a speaker(s) to one of the output jacks and set the
impedance selector to the correct speaker impedance.
Step 3
– Turn all volume and tone controls to minimum positions. The
vibrato intensity and speed controls should be turned fully
counterclockwise. The power and standby switches should remain in the
“on” position.
Step 4
– Plug the amplifier's AC power cord into the AC power source at
the wall.
Step 5
– The panel indicator should illuminate. Monitor for any unusual
smoke or smells or blown fuse. If anything unusual occurs or if loud hum is heard from the
speaker, disconnect power immediately and review all connections. Let the amplifier warm for
2 minutes.
Step 6
– With your multimeter on the 500 volt range, connect the meter's black lead to
chassis ground (photo 8.2a) and carefully touch the meter's red lead to the “B” terminal of the
can capacitor (photo 8.2b). The voltage here should be 345 Vdc.
Step 7
– Move the red lead to the “A” terminal of the cap capacitor (photo 8.2b). The voltage
here should be 320 Vdc.
Step 8
– Move the red lead to turret T55. The voltage here should be around 11 volts Vdc
(photo 8.4a).
Step 9
– Remove both multimeter leads from the amp and set meter to the side.
Signal Injection, Final Testing
Step 1
– With no signal source connected to either input, turn the normal channel tone control
fully clockwise.
Step 2
– Turn the normal channel volume control clockwise and listen for a low level hiss from
the speaker. There may be a slight hum too, but any dramatic hum indicates wiring troubles.
Step 3
– If the above hiss is heard, turn the volume control back to minimum (leave tone
The voltages above as measured at the can cap and the cathode resistor (turret T55) will
vary depending on the idle current of the individual tubes. +/- 15% is acceptable.
NOTE
photo 8.3c
8.4
48 TubeDepot.com
photo 8.4a
8.5
