T
UBE REPLACEMENTS
The MV52 uses eight vacuum tubes of three different types: two 5751
(V1 and V2), two 6FQ7 (V3 and V4) and four EL34s (V5 through V8).
Each type has been carefully chosen for its circuit application. It is well
known that tubes of a given type vary sonically depending on the
manufacturer. We have chosen the brands of tubes that we supply
based on extensive auditioning of available brands. The choice of brand
has been made solely on the basis of sonic performance and reliability
without regard to either cost or prestige. We know of no vacuum tubes
available which will improve the sonic performance of your MV52. Also,
the tubes in your amplifier have been tempered by a controlled burn in
procedure that permits them to perform for a greatly extended period
without degradation in normal use. We highly recommend that, when the
time comes to replace the vacuum tubes, you purchase replacement
tube sets from conrad-johnson design.
The MV52 has been designed to make tube replacement as simple as
posssible. Because the output tubes are individually biased, replace-
ment tubes need not be matched pairs. No a-c balance adjustment is
necessary. It is necessary to re-bias the amplifier when the output tubes
are replaced. The MV52 has built in bias indicators so that no instru-
ments are required to make this adjustment.
ADJUSTING OUTPUT TUBE BIAS
Biasing the amplifier is a simple procedure that can easily be done by
the owner. Only a plastic screwdriver is required. A red plastic screw-
driver has been included with your amplifier for this purpose. After
replacing the tubes, the amplifier should be connected to a load (your
loudspeakers will work fine) and there should be no signal applied to the
amp. It should be connected to you preamplifier with the volume control
turned fully down. Turn the amplifier on. After about one minute, turn
each of the four screwdriver adjustable controls counterclockwise until
the associated indicator LED just goes off. Clockwise rotation may be
necessary first to turn the LED on; do not turn the adjusting screw any
further in the clockwise direction once the LED has come on.
After the amplifier has warmed up thirty minutes, the procedure just
described should be repeated. NOTE: It is normal for these LEDs to
MV52 Owner’s Manual
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