Communication Concepts AN762 Construction Hints - Manual (Page 4)

The 2N5990 and 2N5991 transistors are now obsolete. These transistors had an
unusual pin configuration for which a direct physical replacement is not available. Helge
Granberg from Motorola suggested using the 2N6488 transistor as a substitute.
However to fit the PC board configuration, the transistor must be mounted upside down
as shown in the Figure 3 below.
Figure 3
Position the pass transistor Q3 upside down over the screw hole. Bend the leads to fit
the hold pattern (Note: the metal side of the transistor facing up away from the PC
board). Using the 1/8 inch metal spacer, install the 4-40 x 3/8 inch screw from the
bottom up through the spacer and transistor and install a #4 KEP nut and tighten
snuggly. Solder the transistor leads from the bottom and clip the excess leads.
The transistor D1 mounts on the bottom of the PC board. Position the transistor
D1 over the screw hole . Trim the leads back to fit the lands on the PC board. (Note:
the metal side of the transistor must be away from the PC board, i.e., toward the
heatsink). The collector lead can be trimmed off or soldered to ground with the emitter.
Solder all leads snugly against the board.
Install the ferrite chokes (2). Make sure the lead wires do not short out any of the
turns going through the chokes. Push the chokes down flat against the PC board and
solder. See Figure 4. Clip the excess leads close to the PC board.
Figure 4
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