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| Replacing the power cord |
If your power cord is a
two prong cord, or the third prong ground has been cut off, or the plug is coming off the
cord, or the cord has been cut and has tape wrapped all around it, or your lips are taking
a beating on a microphone, then it is really a good idea to replace the cord with a new
three prong grounded power cord.
It is really important to be grounded properly to prevent
shocks, and the amp will usually run quieter. If you want to preserve the vintage aspect
of the amplifier then you can install the new cord and save the old cord.
Start by making
sure the amp is unplugged and then remove the plastic strain relief bushing around the
power cord where the power cord enters the chassis. Crimp the bushing together with some
vice grips or channel locks. Make a diagram so you know where each wire will be soldered
on the new power cord. Unsolder the two wires that usually go to the ac receptacle or the
ground switch. If there is a third green wire soldered to the chassis then you must cut
the wire off at the chassis because chances are you do not have a soldering iron powerful
enough to unsolder this wire.
Take the new power cord and push it through the hole in the
chassis to see if all three leads will reach where they have to go. If any of the wires
will not reach then you must carefully remove some of the outer plastic casing until you
have enough length for each wire to reach the spot where it will be attached.
The green
wire will be attached to the nearest transformer bolt by using a round terminal lug. You
can use a razor blade knife while bending the power cord over and gently slice the outer
casing. Bend the cord over the other direction and slice it on the opposite side until the
outer casing is cut all the way around. Remove the outer casing piece and test to see if
all the wires will reach. If they do then you must decide where the plastic strain relief
bushing will be on the power cord.
The only way to install the strain relief bushing
without buying the special tool is to crush the bushing into the power cord by using a
vise or some other crunching object. Let the bushing and cord remain in the vise for a couple of minutes. After you
remove the cord and bushing from the vise keep them together just like they were in the
vise. You will need a pair of vise grips or channel locks to compress the bushing enough
to insert the bushing into the chassis hole. This part is sometimes very easy and
sometimes very difficult. Sometimes the new power cord is larger than the old cord and
does not want to go in. Sometimes the amp has a two prong cord that is the size of lamp
cord. In this case the old strain relief bushing will not fit the new cord and the hole in
the chassis is not big enough for a three prong power cord. The only thing I can recommend
here is to use a dremmel tool or a hand file or green lee punch to enlarge the chassis hole and then get a
new strain relief bushing that is the correct size for your power cord.
You might not want
to do this to a vintage amp. In this case you should use a rubber grommet instead of the
strain relief bushing. Use a large plastic wire tie on the inside and outside of the
rubber grommet to keep the rubber grommet from being pushed into or pulled out of the chassis. A grommet
will have a smaller outside diameter than the strain relief bushing and will probably fit. The only
disadvantage to the grommet is that it will allow the power cord to swivel around and the
wires might twist on the inside of the chassis. This can lead to broken wires and a
dangerous situation.
If the amp has a plastic cord clamp on the inside of the wooden
cabinet this will prevent the cord from twisting. After the new power cord is in place,
crimp and solder a round terminal lug onto the end of the green wire on the new power
cord. Remove the nut from a transformer bolt and slide the lug down onto the bolt. You
can also leave that nut there and use another nut to sandwich the ring terminal lug between the
two nuts. Tighten the nut down so that the lug is making good contact with the chassis.
Now solder the black and white wires to their proper location.
Test the amp to see if all
connections where made properly. When you put the amp chassis back into the cabinet, clamp down
the power cord to the wooden cabinet with a plastic cord clamp. |
| Check the fuse size. |
This seems silly but you would be surprised what I have found in the fuse holder. I have
seen 30 amp automobile fuses where a two amp slo-blo fuse should be. I have also seen
metal objects inserted or tin foil wrapped around a blown fuse. Use the proper fuse that
the amp was designed to use. A much larger fuse may cause the power or output transformer to
fail instead of an inexpensive fuse.
If an amp blows a fuse, it blew for a reason, find the reason the fuse blows first, fix the amp and then put in the correct size fuse. |
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