Antempore
or Imbecile Burden
(some call it a "Dummy Load")
I needed a load (simulated antenna) to hook to my HW-101 to tune the transmitter and all I had was a 5-Watt Rat-Shack special. (The Heathkit manual suggests something around 100 Watts.) I've held on to what seems hundred of these cans thinking that someday I'd find a use for them. Here was my chance to prove myself right. Since I knew I'd be filling it with mineral oil to sink the heat from the load resistors I soldered the seam up to make sure it wouldn't leak. |
 |
The basic idea of this came from plenty of sources which suggested using 13 - 680 W 5 watt CARBON resistors in parallel to achieve the required 50 W (or there about's) load.
 |
Next I mounted a connector to a piece of copper-clad phenolic board and attached a short length of coax. I pillaged the connector from another one of the old Motorola Civil Defense radios I've got piled up and it happened to have a cool shield backing which would provide a nice way to seal the thing from leaking. It took some calculating to figure out how to evenly space the holes for the 13 resistors in a circle around the connector. (Did I mention yet I was never real good at math?) |
Heres a better look at the top after I shrunk some heat-shrink tubing around the coax braid.
 |
The resistors stand at attention nicely after being soldered to the PC board/lid. I wanted to keep the leads as short as possible to diminish inductance. Short pieces of heat-shrink insulation were used to stand them off the board. Since heat rises, I'll consider inverting the can when in use to allow the resistors to cause the heated oil to rise to the bottom of the can. (Yes, that's what I said.) |
The perimeter of the hole for the connector was tinned before installation. After it was secured with screws I heated it lightly with a torch to melt the solder under the connector so I'd get a good connection and seal. It's actually starting to look like something now! |
 |
 |
In order to secure the "hot" ends of the resistors a washer was used to hold them together with the center conductor of the coax. I slobered so much solder it decided to stay there. I would later separate the resistors so as to provide maximum oil flow (and so they don't keep each other warm.). |
The picture says it all.
I built this the Sunday after the Republicans took over Congress in 2002, hence the sticker was still stuck to my jacket and seemed appropriate to go along with the American Spirit can. (that reminds me, I'd better call about getting some advertising renumeration for all this. It's the American way.) I'll get some mineral oil in the morning and fill 'er up so I can attach the top. Still considering how to do that. (One thing I'll have to remember is to not fill the can all the way to the top, the resistors will displace some and it'll be important not to get any on the rim in case I use epoxy.) |
 |
