[BC] exciter problem fix of note

[Sid Schweiger]

Michael Patton states:  "Yesterday I was going through a BE FX-30 on my bench and noted spurious emissions at +/- 30 KHz and +/- 60 KHz, about -50 dBc.  Checking the output of the mod osc by itself, I found no spurs.  Hey, I know this one: the electrolytic P/S bypass caps in the PA are dead.  I disassembled the PA module and changed the caps, using 105° caps instead of the original 85° caps (shame on you, BE), and hey, presto! no more spurs.

So far, so good.  Here's the interesting part:  just for kicks, I tested the old caps on a cap checker, and they showed full value!

So let this be a learning experience, that some electrolytic caps are no longer fit for duty even tho they test OK.

Have any others out there had similar experiences, where caps tested good but misbehaved in circuit?"

Dried-out caps causing a widening of occupied bandwidth was a well-known problem with Harris MS-15 and MX-15 exciters.  There were two large ones in the modulated oscillator circuit (but physically located in another module) that, when dried out, would cause the station to occupy the bandwidth of three or more stations.

Sid Schweiger
IT Manager, Entercom New England
20 Guest St / 3d Floor
Brighton MA  02135-2040