11
5
M
AINTENANCE AND
V
ACUUM
T
UBE
R
EPLACEMENT
5.1
M
AINTENANCE
The only regular maintenance required is to keep the amplifier clean. If it is in a location where dust can
settle on it, then dust will eventually accumulate inside the top cover due to the ventilation slots. To
clean it, unplug the line cord and wait 30 minutes. Remove the top cover, which is held in place with 14
Philips-head machine screws (4 on each side, 6 on top). Wipe with a soft cloth or vacuum with a soft
brush attachment. Isopropyl alcohol can be useful for cleaning the chassis, but do not wipe the tubes
with it, as it can remove the markings. If you remove the vacuum tubes, be sure to replace them in the
correct locations. In particular, the 5751 tubes must stay in their same front or rear location, or the
offset trimmers will need to be readjusted (see Section 5.2). Be careful not to damage the control
electronics during cleaning.
5.2
V
ACUUM
T
UBE
R
EPLACEMENT
Although the lifetime of any particular tube is impossible to predict, vacuum tubes last much longer than
most people think. Hopefully, it will be many years before you have to replace a tube in the Minotaur, as
long as the amplifier is not left on continuously.
The system microcontroller monitors output offset voltage, which will probably be the first sign that a
tube needs replacement. If the red LED in the ON-OFF button begins to flash every 10 seconds, it
indicates that the output offset e/- 0.12V. That suggests one of the 5751 input tubes is drifting
and needs replacement, although it may be possible to extend its service life with an offset adjustment.
The other tubes (four 12AT7 and one 12BH7) are more likely to fail on startup, as indicated by the
amplifier going into FAULT mode. Of course, FAULT mode may be caused by issues other than bad
tubes; see Section 4.4.
Vacuum tube replacement is best done at Tavish Design, although an electronics technician experienced
with high voltage equipment may be able to do it. Contact Tavish Design for further advice.
