A while ago there was a thread on the restoration of a model 18. The poster mentioned how colorful the underside of the chassis was with all original “dogbone” resistors and what a shame it is to have to replace many of them. I posted a picture of a dogbone that I had made. I have decided to to post a tutorial on how to do it.

For this tutorial, I’m going to make a 240K 1watt dogbone resistor.

To start off with, we need a piece of plastic tubing about 1/4 to 5/16 inch in diameter, it needs to be cheep and readily available. I found a ballpoint pen that was perfect.

by Steve Davis, on Flickr

I cut the tubing to length, about 1 inch for a 1/2 watt or about 1-3/4 inch for a 1 watt, as in this case. I chuck the pen in the drill press, bring the table up until it just touches the pen. Then cut the tubing using a razor blade attached to a block of wood. This produces resistor bodies of uniform length.

by Steve Davis, on Flickr

Now, cut a small notch in each end to bring the leads out.

by Steve Davis, on Flickr

This is a tool made from an X-acto knife to twist the resistor leads. The prongs were made by heating and bending a large sewing needle into a “J” shape and inserting it into the slot of an X-acto knife handle.

by Steve Davis, on Flickr

by Steve Davis, on Flickr

by Steve Davis, on Flickr

I soldered two 120K ohm 1/2 watt resisters together in series. Then, using 18 ga. buss wire, I extended the leads. I use 6 inches of wire, this gives about a 3-1/2 lead length when finished.

by Steve Davis, on Flickr

I have now inserted the resistors into the tube and brought the leads out through the notches.

by Steve Davis, on Flickr

Using “JB Quick” or “Locktite Weld” (JB Weld is to slow for this job) completely fill the tube. Use your finger to pack the epoxy into one end until it comes out the other. The theory here is, the epoxy will transfer the heat to the outer surface.

by Steve Davis, on Flickr

Now wrap each lead around the tube two times. I started near the end and wrapped toward the middle.

by Steve Davis, on Flickr

Solder the wraps

by Steve Davis, on Flickr

The resistor is now ready to paint. Dip the resistor and sling the excess.

by Steve Davis, on Flickr

by Steve Davis, on Flickr

After the body has dried, dip the end and add the dot with a small brush.

by Steve Davis, on Flickr