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MAINTENANCE / CALIBRATION
Replacing the tubes
Under normal conditions, the tubes in the MM-1 should have a long, hassle
free life but eventually all tubes need to be replaced. With this in mind, the
MM-1 has been designed to use readily available and easily replaceable
tubes that need no biasing or calibration when replaced.
There are two tubes in the MM-1 and it is
important to replace each with the correct tube.
Pentode Tube (located on the main PCB)
The MM-1 ships with an Electro Harmonix EF86 tube in this position.
These tubes also have several variations available as well.
Triode Tube (visible through the front panel cutout)
The MM-1 ships with an Electro Harmonix 6922 tube in this position.
These tubes sound fantastic in this circuit but there are a number of high end
variations available as well.
The only internal adjustment/calibration in the MM-1 is the air adjustment. Like
the original air circuit in the HG-2, the gain of the air circuit can be adjusted based
on the user's preference. The adjustment is a single turn trim resistor located at
the front right corner of the main PCB (looking from the front) and is labeled "air".
As with the HG-2, as you increase the gain, the frequency also shifts up slightly.
12
Air Calibration
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