The purpose of the beads is to make the connections
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to the transistors both high impedance, and lossy at
the frequencies the transistor might try to oscillate.
Any of the of the ferrite bead materials will do the job.
Dennis Tillman W7pF wrote:
Tek uses ferrite beads in some of the transistor adapters they make for
their curve tracers. These beads are inserted in each (E, B, and C) lead of
the adapter. I always assumed the purpose of the beads is to prevent the
transistor from oscillating but I don't really know this for sure.
Does anyone know what frequency band Tek was concerned about or what ferrite
Tek used? There are many ferrite materials to choose from. The few I am
familiar with are FB-43, FB-61, FB-73, and FB-75B.
The 013-0128-00 adapter specifically for the 7CT1N and 5CT1N uses three
276-0507-00 "SHLD BEAD,ELEK:FERRITE" for example. But there is no more
information than this on the one or two page data sheet that comes with a
I would guess Tek would chose ferrite material that is intended for
relatively low frequencies (maximum resistive loss at 10MHz or less) but
that is only a guess.
Dennis Tillman W7pF