13
STAR*TECH JOURNAL/AUGUST 1982
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We recently received a letter from T.W. Davenport, General Manager of Famark
Industries in Victoria, Australia. He had been approached by Philip Barker of their
Service Department regarding Baily's Tech Quiz (Parts 1 & 2). These installments
appeared in our August and September 1981 issues respectively.
In our Vol. 3, No. 6, August '81 issue (Page 13), question #3 read: "When a Transistor
is "on" you have max: _ _ _ and min: _ _ _ ." The choice of answers were A.
Resistance. B. Reactance. C. Voltage. D. Current.
The answer that was published read: D. Current and A. Resistance. Mr. Barker
wondered how an answer of C. Voltage and D. Current could be dismissed as incorrect.
In our Vol. 3, No. 7, September '81 issue (Page 5), question #6 appeared as follows:
6. What is the Voltage gain of the given Circuit?
R:2
30041..
T
A. 5
B. 10
C. Can't be computed
from info given.
~. ~one of the aboveA
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The answer published in the following month's Journal read: E. None of the Above.
Mr. Barker felt that the correct answer should have been C. Can't be computed from
info given. For example, battery voltage is not specified and may not have sufficient
voltage to drive the circuit. Also, the dynamic resistance of the transistor is not taken
into account (no specifications are given for the transistors). Also, the base bias of the
transistor cannot be computed because the battery voltage is not included. Therefore,
no calculation is possible to determine how hard the transistor turns on."
Furthermore ... "Mr. Barker believes the circuit is inoperable due to the collectorofthe
transistor being negatively biased relative to the emitter, as is the base. Being an NPN
transistor, it would not turn on."
In order to satisfy Messrs. Davenport and Barker, Star*Tech Journal approached
Edward J. Schmidt, Marketing Services Manager of Baily's Pinball Division. Mr.
Schmidt had submitted this Tech Quiz for publication in the Journal. His response to us
is excerpted from his recent letter as follows . . .
"After a careful review of Mr. Davenport's letter, I could understand why he and Mr.
Barker would request clarification. It is my hope that the following information will set
the record straight.
Regarding question #3 (S*TJ, Vol. 3, No. 6), the voltage should have been included
under the minimum answer as well as Resistance.
In reference to question #6 (S*TJ, Vol. 3, No. 7) I have to agree with him; the answer
"C" is correct. Therefore, my original answer of "E" should be voided out.
The original answer "E" would be used along with the formula R2 + Rl as a "quick
and easy" method of obtaining the voltage gain for a circuit of this nature. However, I
overlooked the polarity of the battery as well as the unrealistic values for R4 and R6.
They should be more along the lines of 10 kohms for R4 and 4. 7 kohms for R6. Then for
reasonable values of beta and battery voltage (B > 50 and Vee> 5v) the stage is
functional and the voltage gain is dependent primarily on the R2/Rl ratio."
In closing, Mr. Schmidt added, "I would like to thank Messrs. Barker and Davenport
for their time and the efforts they devoted to these issues. Their interest to these types of
matters will help all of us to do a better job."
Star*Tech Journal .wishes to thank both parties for their input and concern in clarifying
the answers to these questions.
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