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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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