Top view, Fuses – Manley REFERENCE PREAMPLIFIER User Manual

Page 10

TOP VIEW

FUSES

6414

12AU7WA

12AT7WA

PHONO

6GF7A

OA2

6GF7A

6072

12AX7WA

6072

12AX7WA

PREAMP

POWER
SUPPLY

TUBE LOCATIONS - See the diagram above for the proper tube locations. Power should be
unplugged and allow the tubes to cool before handling them. Changing tubes on this preamp is a
little more tricky than most because the printed circuit boards are elastically suspended. It is
more important to allow the power supply capacitors to fully discharge when putting tubes into
the sockets. It is difficult to push or pull the board so that it shorts to a grounded jack but .....

The technique to remove a tube is to rock or wiggle the tube around as you gently pull.

To insert a tube, wiggle it in as you gently push. It is safer if the bottom panel is on - there are
stand-offs under the board that are about 1/2" above the bottom panel that should prevent the
PCB from going further than that 1/2".

FUSES - Each of the fuses are 1 amp slow-blow. Un-plug the AC mains before checking the
fuses to prevent any possiblity of a shock. One fuse is for the regulated high-voltage supplies,
the other two are for tube filaments (heaters).
A fuse that has turned black inside is a hint that a "short" occurred. Try another. If this fuse also
blows then there may be a problem requiring a technician but often the problem has a simple,
visible cause. The fuse is a protection device designed to stop power, rather than allowing
potentially expensive damage to the power supply. Replace only with the correct size and value.