USER’S MANUAL
Electronaut M63 Vacuum Tube Microphone/Instrument Preamplifier
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E L E C T R O N A U T C O M P A N Y
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ping at the input stage. Don’t be afraid of the PAD! The PAD circuit consists of very low noise, high-precision
resistors. If you find yourself backing off on the TRIM knob significantly, you might get better performance if you
engage the PAD switch and crank the TRIM knob back up a bit.
If desired, turn the ATTENUATE potentiometer fully counterclockwise and crank the TRIM control fully
clockwise, then use the ATTENUATE potentiometer to set the level. By all means, experiment with various
combinations to find the sound that best suits the material.
Note: If the output of the M63 is either driving very long cable lines or plugged into equipment with a low (i.e.
600 ohms) input impedance, the ATTENUATE potentiometer should be set in the fully clockwise position for best
performance. Again, experiment at will, but the recommended setting will probably produce the best result.
The procedure for setting the gain structure for the instrument input is identical to the procedure for microphones
with the exception of the 20 dB PAD option, which is not available while in INSTRUMENT mode.
For the best tube life, turn the M63 OFF when not in use; however, it is good to avoid a lot of unnecessary ON/
OFF cycles. As a rule of thumb, leave the M63 on unless you know it will not be used for the next several hours.
Suggestions
It is always good practice to use the shortest possible signal chain between the microphone and the recorder.
Excess in-line connections between the microphone and the M63 such as patch bays, splitters, etc. should
be avoided as a general rule to avoid the gradual deterioration of the signal quality due to increased cable
capacitances, contact resistances, adjacent noise sources, etc. Whenever possible, keep microphone cables away
from AC mains cords, power strips, etc.
Avoid stepping on your microphone cables, and train your friends, clients, and everyone else to do the same!
Replacing the tubes
The M63 is designed with a high voltage power supply utilizing an indirectly heated dual diode rectifier tube,
which naturally has a very slow startup time. It takes about 30 seconds for the high voltage power supply to
reach 98% of the operating voltage after the unit is initially turned on, which provides very gentle treatment to
the tubes, and should directly lead to increased tube life. The tubes shipped with the M63 are high quality and
should provide years of high performance, low-noise amplification. However, all vacuum tubes have a finite life
and will eventually need to be replaced.
The input gain stage consists of a premium 12AY7/6072A dual triode, and is located on the outside edge of the
amplifier circuit boards, furthest from the power supply. This tube is selected for low noise and microphonics.
The output stage consists of a 12AU7/ECC82 dual triode, and is located on the inside edge of the amplifier circuit
boards, closer to the power supply. This tube should also be chosen for low noise and microphonics, although it
is less critical than the 12AY7/6072 tube.
The rectifier tube is a 12X4 dual diode, and is located in the center towards the rear of the M63, behind the
toroidal power transformer.
Replacement tubes of all types are available from directly from Electronaut.
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