The crOwBX project: The LS318 Dual Transistor

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Two LS318 dual transistors are used for each crOwBX voice card. As of August 2013 Linear Systems no longer offers the LS318 in the plastic DIP (PDIP) package. While Crow thinks this is silly--especially since they offer the circa-1960s TO-71 and TO-78 packages (must be all those legacy miltary radar systems that need to be kept in service)--the fact remains a different LS318 package will be needed. A future voice board revision will use the SOIC-8 package as well as provide pads for the TO-78 package, but the rev2 can also use the TO-78 with a little leadforming aka bending the lead wires with needle-nose ot flat-nose pliers so as to fit in the DIP pads.

The LS318 in the TO-78 metal can package has 3 leads per side. Using pliers and gripping the leads about 0.125" or 3mm away from the base of the part, bend all the leads of one side at the same time: first bend out at about a 45-degree angle then move the plier down the length of the leads a few mm and bend back toward the center. Do the same thing for the other set of leads and try the part in the DIP pad area of an LS318 on the voice board. The tab points up toward the top edge of the board and the leads use pads 1,2,3 and 6,7,8. Pads 4 and 5 are left open. After a couple lead bending adjustments for the best fit the result should be very similar to the images shown here:

One note: there is no ceramic base pillar on the LS318 as is common in parts like a T-series opamp. Therefore, just estimate the mounting height to be about 0.375" or 9.5mm overall from the board to the top of the can. The 1K temperature compensator will sit just underneath the body of the part with about 1.5mm clearance. The tempco is thermally connected to the package using three of the package pins (2,3,6) so thermal grease is not strictly necessary.

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Scott Rider "The Old Crow" -- 0ldcr0w@0ldcr0ws.n3t