Manley MAHI MONOBLOCK AMPLIFIER - Manual (Page 10)

10
MAINS FUSE: If this has blown, A Very Bad Thing has occurred. See page 3.
B+ FUSE: The B+ fuseholder is located on the rear chassis near the speaker binding posts. If all of the
sardine NONE of the tubes show any bias reading at all, and the lights are on, and no tunes will play, you
might have popped a B+ fuse. This fuse is here to protect the output transformer from a rogue tube or some
other strange event. Before replacing it, stop and think a minute if you noticed anything, like a bang or crack
noise coming from the speaker. Or maybe you notice one of the tubes looks cracked or sick. Or maybe you
smelled something funny? And saw a tube take off and glow bright red or orange? Any of these events could
be a tube "running away". If you are aware of what went down and can clearly see the offending tube, then
yes, do replace the bad tube and then replace this B+ fuse. Always check the bias on a new tube as the
amplifier warms up and watch him closely like a new puppy to make sure he behaves for the next little while.
The fuse is a 4/10th Amp, 250v MDA 4/10 SLO-BLO (time delay). The size is 1/4" x 1 1/4". Only use a
ceramic fuse here as the glass ones sometimes flame out or crack. Do not use a Fast Blow fuse or you will be
replacing them on every downbeat. And remember those 400 volts we mentioned? They are living here on
this fuse, so you had better MAKE SURE THE AMPLIFIER IS OFF AND UNPLUGGED AND
DISCHARGED before you play with this!
SWAPPING TUBES: 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 exact replacement for the 6414 dual triode,
although the 12BH7 or 12AT7 are pin-compatible substitues, so in a pinch you can jam one of those in to get
you by for a few days. The 6414 is really the best choice here, for this circuit, trust us. Actually think long
and hard before just trying to score some golden lovely tubes on ebay for $125 each. Are they really what
they claim to be? (Paint can be scraped off or applied at will.) Are they really new? (Hard to tell sometimes.)
Are they tested? Were they tested for optimum performance in a Manley MAHI? We didn't think so. By
virtue of our experience, testing, and selection we do recommend you obtain replacement tubes from the
factory. We will indeed be looking after the best interests of you and your MAHI in our tube selection
travails.
Digging around inside:
Yes there are user-servicable parts inside! (Contrary to what The Safety Regulatory People tell us to declare
on the rear of the chassis, and you have to be a handy kind of user...) 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 you are planning to get inside and dig around in there. If the amp has
been powered up within the last 15 minutes stop! and let the large electrolytic capacitors discharge otherwise
you could still get a shock even though the unit is unplugged. Really! You will need a #1 Philips screwdriver
to remove the bottom cover screws. Use one hand only when reaching into the enclosure or touching any
components inside. Keep the other hand away from the amplifier, preferably in your pocket. For real!
BACKLIT BADGE LAMP REPLACEMENT: If the tubes are glowing and you have tunes but the
MANLEY MAHI 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 MAHI illuminated badge
under the aluminum bracket. Don't crush & break the glass. NOTE! MAHI's shipped after 5/2003 use
LED's to light up the badge, so guess what? You will never have to replace these! Hooray!
Please direct any other more involved questions regarding the guts of the MAHI to
MANLEY LABS Tech Support for further assistance.
Taking advantage of the amazing technology of email: [email protected]
is the best way to reach us, because we might be eating lunch or something.