Manley JUMBO SHRIMP - Manual (Page 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-pow-
ered 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BACKLIT BADGE LAMP REPLACEMENT: Chances are, you have a newer version of the JUMBO SHRIMP
that uses ultra long-lasting LEDs for badge illumination. These LEDs practically last forever, so it’s likely you’ll
never have to read the next paragraph.
However, if your unit is older (Serial # MSP054 and below)....
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 incan-
descent 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 illumi-
nated 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 suscepti-
ble 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-compati-
ble 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: <[email protected]>
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