Lawson L251, Operation Manual

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of the original U 47 low frequency characteristics ( no low
frequency rolloff ). The - BASS position provides a 6 dB / octave
rolloff below 100 Hz ).
Vacuum Tube Your tube mic uses the 6 N 1 P vacuum tube . This
tube is a standard nine - pin vacuum tube . All tubes used in
Lawson tube mics have been specially selected for extremely
low noise . It is important when replacing this tube to obtain a
low noise 6 N 1 P tube that has been selected for low noise
characteristics specifically related to use in microphones .
Lawson , Inc ., can supply these specially selected tubes . To
further insure low noise , an innovative , low - loss tube socket is
utilized employing military grade , heavily gold - plated
beryllium copper contacts , resulting in unparalleled grip , low
contact resistance , and long life .
Replacing the Vacuum Tube . To remove the vacuum tube ,
first unplug the power supply cable from the mic . Disassemble
and remove the mic holder by removing the two wing / thumb
nuts exposing the base of the microphone as seen here .
Remove the two Phillips screws on the bottom of the
microphone . The C / MP plate
and the body cylinder can then
be removed exposing the
internal vacuum tube and
circuitry . Grasp the tube and
pull straight down toward the
base of the microphone , taking
care not to use sideward
motion which could bend the
tube pins . Make sure the pins
are straight on your new tube
by using a tube pin straightener . Line up the tube pins with
the socket and push straight in . Replace the body cylinder .
Replace the C / MP plate making sure to line up the toggle
switch handle with the hole . Replace the two Phillips screws .
Do not over - tighten . Reassemble swivel mic holder .
informative to have the power supply in the control room and
make pattern adjustments while monitoring a performance to
find the ideal position . Make sure your microphone is set to
the MP mode by checking the position of the switch on the
base of the microphone . The polar pattern control is
disabled in the C mode . A blue LED inside the windscreen
glows when the multi - pattern mode is selected .
It is normal to experience a slight low - frequency noise while
the pattern control is being rotated . The pattern change is not
instantaneous . Please allow five to ten seconds for the new
pattern to stabilize after readjustment .
10 dB Pad Output may be reduced by 10 dB with the switch
located on the left - hand side of the power supply unit . Note!
Turn down the microphone channel at the console before
changing the position of this switch to prevent transient
thumps . The -10 dB pad switch actually lowers the capsule
polarizing voltage thus lowering the input level to the vacuum
tube and raises the sound pressure level capability . To
preserve the low noise floor , use the -10 dB position for
extreme sound pressure levels only .
Low Frequency Contour Control (- BASS / L 251

L 47/+ BASS ) A two - position low frequency contour switch is
located on the front of the universal power supply . This switch
can be changed during a performance without transient clicks
or pops . The FET electronics provide the same low frequency
effects .
With the L 251 capsule , the L 251 ( or - BASS ) position provides a
faithful reproduction of the original ELAM 251 ( a 6 dB / octave
rolloff below 100 Hz ). The + BASS position provides extended
low frequency characteristics and more profound proximity
effect ( actually a flat frequency characteristic ).
With the L 47 Quick Change™ Capsule on your tube electronics ,
the L 47 ( or + BASS ) position provides a faithful reproduction