Sencore TF151 - Checking Regular Transistor AC Beta; Testing Connections and Setup

Silicon rransistors have a very low leakage currenr while germanium may have a
fairly low ro quire high leakage depending upon rhe applicarion. TIle chan below is
a rough guide to help derermine if rhe leakage is roo high. When in doubr, consulr
rhe Sencore Reference Book.
Transistor Type
RF-IF
Audio
Power
Germanium Transistors
Leakage Currenr (max)
0-5 microamps
.5-50 microamps
50- 5000 microamps
Silicon Transistors
Leakage Currenr (max)
0- 3 microamps
0-5 microamps
5-500 microamps
CHECKING REGULAR TRANSISTORS FOR AC BETA IN on OUT OF CIRCUIT
The regular or bi-polar rype rransistor can be easily checked in or our of circuir for
acrualAC bera wirhrhe TFlSl. Three ranges are provided, LO POWER, IfI POWEH
and SPECIAL R F. Mosr rransistors will fall in rhe LO POWER c lassificarion and
mosr of rhe resrs will be performed wirh rhe TFlSl Funcrion swirch ser to rhe LO
POWER range. If rhe rransistor has a power dissipation of one watt or more, it is
genera lly considered a HI POWER transistor and should be tested with the Function
switch in the HI POWER position. TIlese transistors will be marked with a (v) in the
Sencore Reference book. The SPECIAL RF setting is for the low saruration drift
field type transistors such as tLe GE9 replacement type and other critical R F tran-
sistors. These transistors will be marked with an asterisk (*) in the Sencore Ref-
erence book. If the transistor is used in. an RF or IF application and is not marked
for the SPECIAL RF check, it will normally be tested under the LO POWER check.
If the beta appears too low or the meter reads a beta of less than one, the transistor
may be sarurating early. The transistor should then be checked at a low er current
with the SPECIAL RF check posirion on the TF1Sl. The connecrions for testing the
transistor in or out of rhe circuir are the same. The only rhing thar will change is
rhe Function switch posirion depending upon the type of transistor resred.
To connecr rhe TFlSI for res ring:
1. Connecr rhe E, 13, and C rest leads to rhe transistor as shown in figure 3 or 4.
NPN
BASE
COLLECTOR
(+Vl
EMITTER
'PNP
COLLECTOR
(-VI
EMITTER
RED LEAD
COLLECTOR
YELLOW LEAD
BASE
BLACK LEAD
EMITTER
Pigure 3. Connecring To A Transistor For In-Circuir And Our Of Circuir Tesring
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