Owner manual

10
REPLACING a TUBE or the INDICATOR LAMP.
Yes there are user-servicable parts inside! (Contrary to what The Safety Regulatory People tell us to
declare on the rear of the chassis.) But, as with other vacuum tube based products, there is also high
voltage present. Therefore caution must be used when covers are removed; otherwise there could be
shock hazard. Probably not enough to kill you, only enough to severely annoy you should you
inadvertently grab onto the B+ volts. As with all mains-powered gear make sure the mains power is
off and mains cord is unplugged. If the preamp has been powered up within the last 15 minutes stop!
and let the large internal capacitors discharge otherwise you could still get a shock even though the
unit is unplugged. You will need a #1 Philips screwdriver to remove the cover screws.
BACKLIT BADGE LAMP REPLACEMENT: If the tubes are glowing and you have tunes but the
MANLEY SHRIMP badge fails to light up, you may have a burned out badge bulb. This little light
bulb looks like a fuse but it is really a light bulb so don't try to put a fuse in there. It is sometimes
called a "fuse-lamp" and is 1/4" diameter by 1 1/4" long. It is a 12volt, 0.15 Ampere incandescent
lamp. If you need a new one and can't find one readily, you can guess that we probably have plenty in
stock and you could order a new one from us. After removing the cover, use a small slot driver to help
pry the badge’s fuse-lamp straight down out of the clip holder. It is of course located right behind the
MANLEY SHRIMP illuminated badge under the aluminum bracket. Don't crush & break the glass.
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.
TUBE REPLACEMENT: Increased noise level whether gradual or abrupt can generally be
attributed to aging tubes or sometimes just rebellious teenage 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. We sometimes call this noise “grotzels”.
Should these symptoms appear, cast your suspicions first on the input tube (12AT7) in that channel.
(They are the shorter tubes, the ones to the LEFT of the chassis, looking down from the front of the
unit.) If it is happening only in one channel, try swapping the two input tubes channel-to-channel and
see if the evil noise switches to the other channel, if so then you have found your troublemaker. (The
RIGHT channel is on the bottom.) If the Evil Noise just goes away, then consider yourself un-cursed
and have a nice day listening to some tunes.
If one tube were being replaced in one channel for some reason after many years of operation, it
would be wise to replace the same tube in the alternate channel, preferably with matching
manufacturer and date code if possible. Do NOT swap the input 12AT7 tubes with the output 7044
tubes. These two tube types have different pin-outs and you might break something.
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. 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 tube
socket. Be careful to put replacement tubes in the proper sockets. 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 the preamp!
Three tube types that are electrically and plug-socket compatible with the 12AT7A dual triode include
the 6021, 6679, and the ECC81. There is no direct replacement for the 7044 dual triode, although the
6900 or 5687 are pin-compatible substitues. We have no experience with either of those two types and
thus cannot vouch for their worthiness in the Shrimp. The 7044 is really the best choice here, trust us.
Please direct any other more involved questions regarding the guts of the Shrimp to
MANLEY LABS for further assistance.