Manley MOVING COIL & MOVING MAGNET PHONOGRAPH PREAMPILFIER - Manual (Page 8)

OPERATIONAL NOTES
PREPARATION FOR INSTALLATION
Budget a suitable space in which to place the preamplifier, and associated interconnect cable. This space
should be free of strong external magnetic and RF fields, and reasonably removed from strong loudspeaker-
generated acoustical fields. This space should also be free of excessive heat or dust and large enough to
permit easy flow of cool air to the top, bottom and sides of the preamp.
REPLACING A TUBE
Yes there are user-servicable parts inside! But, as with other vacuum tube based products, there is also high
voltage present. Therefore caution must be used when covers are removed as there could be a shock hazard.
With all mains-powered gear make sure the power switch is off and mains cords are unplugged. If the preamp
has been powered up within the last 15 minutes stop and let the large internal capacitors finish discharging.
You will need a #1 Philips screwdriver to remove the cover. Use one hand only when reaching into the
enclosure or touching any components inside. Keep the other hand away from the preamp, preferably in your
pocket.
Increased noise level, whether gradual or abrupt, can generally be attributed to aging tubes. Gradual noise
increase from weakened tube cathode emission is the chief symptom of an aging tube, which may be
accompanied by exaggerated distortion or loss of headroom. The noise may be a variation in the level of hiss,
or the noise may develop a more granular “large-curd” quality. Should these symptoms appear, unplug the
tubes in the offending channel and replace with new devices of known-good quality. If the front-end tube is
being replaced in one channel, it is wise to replace the same tube in the alternate channel, preferably with
matching manufacturer and date code if possible.
Let the preamp tube(s) cool down, if necessary, before handling. Tube heater filaments are somewhat more
susceptible to damage when warm or hot.
Each tube should require only moderate force for removal and replacement. Gently rock the tube back and
forth a bit during removal or replacement. Avoid bending the circuit board.
Notice that each channel’s tube heaters are connected in series, so if one tube
goes out in that channel, both of the tubes in that channel will go dark. If one tube is not installed, the other
tube will not light. This is akin to those old series connected xmas tree lights. So if you are trying to figure out
which tube is not working, swap one tube at a time to the other channel until the other channel dies and
sound is restored to the “bad” channel and then you will know which tube has burned out. Swap input tubes
first, and see if the problem moves. Then swap the output tubes and see if one of those is the bad guy. When
troubleshooting by substitution, remember to always only change one thing at a time!
Never substitute other type numbers of 9-pin tubes without careful research. There are literally thousands of
types that share the 9-pin mechanical basing arrangement, but NOT the internal electrical connections!
Mechanically compatible tube plugs and sockets by no means indicate electrical compatibility! And random
experimenting can easily and quickly destroy the substitute tube and other parts of your preamp!
Three tube types that are electrically and plug-socket compatible with the 6922 dual triode are the 7308,
6DJ8 and the ECC88 / E88CC. Please direct any questions to your dealer or MANLEY LABS for further
assistance: [email protected]
Be careful to straighten any bent
tube pins prior to installation; pin misalignment will make fitting the replacement tube difficult or impossible,
and may damage the socket.
Chinook Owners Manual 6
MANLEY
LABORATORIES, INC.