Radio Doings May 22, 1927 - AmericanRadioHistory.Com

May ¿I Radio Doings 27
enormous capacity of 2 to 10 mfd., but
can expect almost anything In advanced
regenerative a n d super. regenerative
sets.. While I can appreciate that one
stage of TRF plus regenerative detector
is superior to TRF with straight detector,
I have come to the conclusion
that no matter how regeneration is
obtained in TRF amplification, the results
are the same. While I may be
entirely wrong in this conclusion, I
would like the favor of your opinion.
ANSWER -The cascade regeneration
principle described in the article to
which you refer is more efficient than
the other types you mention. for the
reason that the regeneration control
does not disturb the proper B and C
voltage relationship, which is essential
not as efficient a method of regeneration
control as the actual tuning by inductance
of the plato circuit. Tuning by
inductance is always more efficient than
tuning by capacity when the tuned circuit
is followed by a vacuum tube for
the reason that a higher voltage is built
up to impress upon the grid of the tube.
The capacity used as a coupling in the
arrangement described should be 2 to 10
mtnfd.
Many readers have requested diagram
and Information on the construction of
an A -B -C eliminator which employs no
batteries or electrolytes. We are giving
full details of such a unit employing
the new QRS 400 -milliampere tube.
The power tube filament current is suprpm
ruso IOW OR
C LI-C1.IMrG
10S MKS tuM iVpl.r4 U-C4.1.AIM
for efficient tube operation. A vacuum
tube, to operate at maximum efficiency.
either as RF amplifier, detector or AF
amplifier, must have a certain definite
relationship between the plate voltage
and the biasing grid voltage. in other
words, if your RF tube is to perform
efficiently as an RF amplifier without
distortion you must maintain the 11 -C
relationship.
The potentiometer method of regeneration
control, is simply a means of
varying the grid potential. This shifts
the operating point on the characteristic
curve, and results in distortion, since
the plate potential has remained constant.
The second method you mention,
that of using a variable resistance in the
plate circuit, causes a change in the
plate voltage without any change in
grid voltage, bringing about the same
undesirable condition noted above, resulting
in distortion. While the third
method mentioned in your question does
not upset the R -C voltage balance, it is
C7. fNrC %4. - 2- 9-
./....own eua o0
plied at a voltage of 5 volts, but the filaments
of the rest of the tubes of the
set must be wired In series and the grid
biasing carefully adjusted. The diagram
of a 5 -tube TRF receiver altered
to adapt it to this power pack will be
given next week.
Pl Is the primary of the transformer
tapped for 120 volts, 110 volts and 100 -
volt A. C. -50.60 cycle.
S1 is the secondary of the transformer
used to step up the voltage and operate
the Rectifier tube. Values should be 360
V. at 300 M. A. load or 375 volts at no
load.
S2 is the coil or secondary of the
transformer and is used to operate the
ionizer, value 4 volts at 5 amps.
S3 is coil for the A. C. filament supply
value 5.5 volts at I amp.
TI is the total transformer.
C1 and C2 aro the buffer condensers
of .1 mfd. capacity each: 600 volts D. C.
working voltage.
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