Over the past few decades, the standard line voltage in the United States, and perhaps elsewhere too, has been increased from 110 to 117 to 120 volts. Needless to say, the gear produced for operation on 110 volts will run considerably hotter today than it's designers ever intended. The following easy to build project from Ed Richards, K6UUZ, provides a cheap and practical solution to this problem.
Thanks, Ed, for writing this up and
allowing BAMA to help spread the word!
First, let's make sure we are singing from the same sheet of music. Let's review some
facts:
In power circuits the white wire, the silver screws (called white), and the wide slot on
outlets are the neutral connections which go to ground at the service entrance. This
circuit should never be interrupted by a switch, fuse, breaker or anything else.
The black wire, brass screws and the narrow slot on outlets is the hot wire and is fused,
switched, etc.
A red wire, if present, is the other hot leg of a 240 volt circuit.
The green wire, green screws, and round hole in outlets is the safety ground and connects
the metal housing of appliances to ground at the service entrance independent of the
neutral.
If your service cord wires are not colored, check with a continuity checker to see which
wire goes to the prong that goes in the wide slot in the outlet. This is the white
(neutral) wire.
Parts List:
1 ea. Metal, electrical, junction box 4" square and 2-1/4" deep.
1 ea. Metal 1/2" raised cover for above with holes for a switch and a duplex outlet.
1 ea. Duplex outlet (as small as possible, like cheap).
1 ea. Roamex cable clamp for a 1/2" knock-out (KO).
1.ea. 3-wire cord and plug.
2 ea. #10 X 1/2 machine screws and nuts.
1 ea. #6-32 X 3/8" pan head machine screw.
1 ea. Wire nut for #14 wire (orange).
1 ea. Crimp-on lug for #12 wire (yellow).
1 ea. Crimp-on lug for #14 wire (blue).
1 ea. Adhesive paper label 1-1/2" X 3"
4 ea. Adhesive rubber feet.
1 ea. Transformer, 120 VAC primary, 12 VAC ct secondary at 3 amperes. Radio Shack
#273-1511 or equivalent.
Assembly Instructions:
1. Orient box as shown and knock out the 1/2" knock-out. install cable clamp.
2. On the outlet, break off the plaster ears on both ends and the jumper between the brass
screws.
3. Place transformer in box per sketch, with the left side tight against the left side of
box. Be certain the wires are not between the transformer and the box. Mark the holes for
the feet. Remove transformer, drill and deburr two 3/16" holes.
4. Install transformer with the primary side against the box and one primary wire going
each way, per sketch. Use the #10 hardware. Be certain primary wires are not between
transformer and box.
5. Pass end of service cord through cable clamp into box. Separate wires for 3".
Strip 1/4" of insulation from the white wire and install the yellow lug. Strip
1/4" of insulation from the green wire and install the blue lug. Strip 1/2"
insulation from the black wire.
6. Fasten the white wire (yellow lug) under the bottom (on drawing) white screw. Bend the
lug under the outlet.
7. Fasten the green wire (blue lug) under the green screw.
8. Strip 1/2" of insulation from all transformer leads. Be sure to hold leads tightly
so you don't pull them out of the transformer. Bend a hook in all the leads except the top
primary lead.
9. Fasten one end of the secondary winding under the top brass screw.
10. Fasten the secondary winding center tap to the bottom brass screw.
11. Twist the bottom primary lead, the other end of the secondary winding and the black
wire from the service cord together and screw on the wire nut. Tuck this down, out of the
way.
12. Fasten the top primary lead to the top white screw.
13. Be certain none of the screws are touching the box and plug in to the wall. Using a
voltmeter or a table lamp, try the outlets to see if the voltage is higher or lower than
the wall outlet. If lower, proceed to step 14. If higher, reverse the ends of the
secondary winding and be certain it is now lower.
14. Unplug the service cord and install the outlet in the cover as shown, using the #8
hardware that came with the cover. Install the #6 screw in the center hole of the outlet.
15. Install the cover on the box using the #10 long screws that came with the cover.
16. Mark the label as shown and install over the switch holes. Install the rubber feet on
the bottom. Tighten the cable clamp.
17. Open a beer; you are finished.
As a rule of thumb, Radios made in the 30's and 40's should be plugged into the 110
outlet. Radios made in the 50's and 60's should be plugged into the 116 outlet. Newer than
that can be plugged into the wall. Do not exceed 3 amperes as that is the rating of the
transformer. If you need more current you can use a larger transformer. I use a 12 amp
multi-tap transformer I got from Fair Radio. Thank you and good luck.
Ed Richards, K6UUZ
A note from Steph Kerman pointed out that you need to make sure that the secondary connections are phased correctly. Otherwise you will get 132 volts instead of 110 and 116. Test the output voltage with a meter before hooking up your vintage equipment to a voltage reducer.
Ken Gordon, W7EKB, has also come up with a voltage reducer. Here is the schematic.
