Installation of Tubes and Tube Cover
Caution: To prevent electrical shock make sure that the AC POWER CORD IS NOT CONNECTED TO THE MC275 when inserting or removing Tubes, as there are hazardous voltages present at the pins of the Tube Sockets.
Your MC275 has gone through an extensive series of per- formance tests during the manufacturing process. The MC275 is supplied with the actual Tubes that were used to test and confirm the performance of this amplifier. To pro- tect the Vacuum Tubes from possible shipping damage, they are packed in four layers of foam and placed into the Tube Cover. It is secured to the MC275 Chassis.
Note: Gloves or a soft cloth will prevent “fingerprinting” of the Tubes during their installation.
1.Orient the MC275 so the Front Panel is facing you.
2.Remove the Tube Cover from the MC275 Chassis by lifting up on both sides. Refer to figure 1.
3.Orient the Tube Cover to the wide opening along one side of its longer dimension. Refer to figure 2.
4.Remove the first layer of foam to expose the Tubes. Refer to figure 3.
5.Carefully remove the Tubes from the remaining pieces of foam and temporarily place them in a safe location.
6.Remove the remaining foam from the Tube Cover and retain all four pieces for possible future use.
The MC275 Chassis has nomenclature screened on it to specify both the circuit location and Tube Type for each channel. Refer to figure 4.
Note: It is extremely important to insert the Tubes in the correct location.
Power Output Tubes:
1.Orient the Chassis so the Front Panel of the Amplifier is facing you.
2.Locate a KT88 or 6550 Power Output Tube.
3.On the top left side of the amplifier, locate the Tube Socket that has the nomenclature V8 KT88/6550 next to it on the chassis.
4.Orient the Tube so the key on the base of the Tube is aligned with the corresponding key on the Tube Socket.
5.Carefully insert the Tube into the socket until the base of the Tube is fully seated in the Tube Socket.
6.Repeat the above the steps for the remaining 4 Power Output Tubes.
There are two different types of Small Signal Tubes (12AX7A and 12AT7) used in each channel. Tube type can be found on the outside of the Tube. The MC275 will not function if they are inserted into the wrong socket.
Tinnerman Clip Fasteners
Tube Cover
Figure 1
Figure 1
Tube Cover with Layers of Foam and Tubes
Figure 2
Power Output Tubes Small Signal Tubes
Figure 3
V8 KT88/6550 Tube
V1 12AX7A Tube
Figure 4
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