old US Telephone hybrid ('Network' block)

I found the following using google from a 1985 article. The trick seems to be to melt it: "To make sidetone adjustable, remove R4 (R5 in European networks) and replace it with R11 (for European networks use R12). The Western Electric Network comes point-to-point wired and sealed in a can; the other networks are mounted on PCBs. To remove R4 from the Western Electric network, the can has to be opened by bending the holding tabs. Don't be surprised to find that the network has been potted in a very sticky, odious paste that has the texture of hot chewing gum and the odor of unwashed shirts. (This material - alleged to be manufactured according to a secret formula - will not wash off with soap and water. The phone company has a solvent for it, but because one of the secret ingredients is said to be beeswax, ordinary beeswax solvents such as gum turpentine, mineral turpentine (paint thinner or white spirit) and kerosene will work.) To remove the bulk of the potting compound, heat the opened can for 30 minutes in a 300 degree F (148 degree C) oven, or apply heat from a hot hairdryer or heatgun. You can also put the can out in the hot sun under a sheet of glass. Don't use too much heat because the plastic terminal strip may melt. Even with a film of compound remaining on it, the network can be worked on." http://www.machacking.net/kb/files/phonepatches.txt Hmm, I've made similarly sticky stuff using beeswax and lanolin and a bit of varnish. Old-timey potting compounds are nasty. --Chuck