Rationalizing the Autodyne
written in 1933 (era of the Great Depression), this article on the autodyne
receiver has a good discussion of noise sources and how to trade off
amplification for signal intelligibility. It originally used the De
Forest Audion vacuum tube amplifier. Noise figure and noise temperature
were not commonly used at the time, but the concept is encompassed in
the treatment. So, what is an autodyne? It is a form of regenerative
circuit that, rather than being tuned right at the signal of interest,
is tuned slightly off center. It functions as a sort of combined local
oscillator and amplifier for demodulating CW (Morse code) signals. Technical
writing styles have not changed much over the decades, even as the terminology
January 1933 QST
of Contents]These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. All copyrights (if any) are hereby acknowledged.
Rationalizing the Autodyne
A Three-Tube Regenerative Receiver of Unusual Performance
George Grammer, Assistant Technical Editor
The development of
the autodyne receiver for c.w. reception has been a continuous battle
for sensitivity and more sensitivity. From the days when a low-loss
detector and one-step was the last word in ham receivers to the present
era of screen-grid r.f. amplifiers and screen-grid detectors the chief
object has been to build sets which would give more noise output for
the least signal microvolt input. The latest contribution is the new
56-57-58 series of tubes, which undoubtedly have it "all over" their
In the meantime some other rather desirable characteristics
that receivers should possess seem to have been lost in the shuffle.
To be sure, amateurs who have built new receivers whose operation has
delighted them, occasionally put forth a few half-hearted claims about
"selectivity" - not particularly because the receiver is really more
selective but because it's the conventional thing to do. The fact of
the matter is that in the set which has become the standard amateur
receiver - one r.f., regenerative detector, and one audio - sensitivity
and effective selectivity just don't go hand in hand. When you get one
you don't get the other, and vice versa. Since both are desirable, it
ought to be possible to select whichever of the two is needed under
any particular conditions. Then our autodyne receivers would be in a
position to give us some real service.
Where R.F. Amplifiers
Superficially it might seem that unlimited sensitivity would be the
height of desirability but, as in all things, there is a limit. That
limit is the noise or background level. If a signal is down below that
level no amount of amplification in the world will bring it up to readability.
This noise level, it should be understood, is not only noise picked
up on the antenna, which may at times be very low, but also includes
tube noise. Almost any tuned r.f. receiver will give out a hiss that
can be heard a couple of feet from the phones with the detector oscillating
even if the set is completely shielded and the antenna is disconnected.
A lot of it comes from the r.f. stage, as taking out the r.f. tube will
show. Our old receivers didn't do that, but the same noise was there,
nevertheless. We hear the signals a lot louder today, but it is questionable
whether we hear any weaker ones than we used to. The old receivers used
to get down to the background level, too.
Five Knobs but Single-Control Tuning
account for the two upper knobs. The others are the tuning, regeneration
control and gain. This set is not particularly compact, having been
made big enough to sit still on the operating table when being tuned.
This is not an argument
against using r.f. amplifiers nor against high sensitivity, but an r.f.
amplifier may not be all beer and skittles. It happens that a regenerative
detector is at its best when the incoming signal is weak; that is, the
sensitivity decreases rapidly as the signal becomes stronger. R.f. amplifiers
therefore don't give the increase in signal strength that might be expected,
because the detector sensitivity goes down as the r.f. gain goes up.
This would be distinctly favorable were it not for the fact that the
detector can't work right on both weak and strong signals. If the circuits
are adjusted so that the detector is highly sensitive to weak signals
it will be highly unsatisfactory on the strong ones, and vice versa.
The unsatisfactoriness arises from the fact that an oscillating detector
adjusted for maximum sensitivity will be "pulled in" by a moderately
strong signal - that is, the frequency of oscillation tends to become
the same as that of the signal - and it is, therefore, difficult to
heterodyne the incoming signal to get a beat note. Strong signals, instead
of becoming loud in proportion to their strength, simply spatter out
over several divisions on the tuning dial and are often harder to copy
than weak ones. Worse still, in the course of spattering they wash out
any weaker signals in their immediate vicinity. Thus the strange result
that a tuned r.f. stage, simply because it brings practically all signals
up to good strength, may decrease the effective selectivity of the receiver
in spite of the fact that it is supposed to add to it.
Now that the question of selectivity
has been brought up, we really ought to get straight on just what we
mean by the word. There are several kinds of it. Usually one thinks
of r.f. selectivity as a measure of the ability of the receiver to separate
two signals of about the same strength on adjacent frequencies. The
difference in this respect between any two tuned r.f.-regenerative detector
receivers of the same general type is rarely worth talking about. It
depends upon factors not readily overcome in this type of receiver,
as James Lamb has pointed out in a previous article.1 We
can wipe this kind of selectivity out of the present discussion - it
takes a "Single-Signal" receiver to get enough of it to be worth while.
But there are other types of selectivity that can and should be
obtained in the autodyne receiver. One of these is freedom from interference
from local stations working on frequencies somewhat removed from that
of the desired signal. This includes interference from local broadcasting
stations. If you have a ham neighbor a few blocks away you should be
able to copy signals within at least 20 or 30 kc. of his frequency.
But very few autodyne receivers we have seen will do it. Local stations
usually cut a large swath out of the band and their key clicks can be
heard over most of the rest of it, whether the receiver has a tuned
r.f. stage or not. As for local broadcasting stations, either you hear
them or you don't. If you do, there is no need for us to point out that
that type of interference is, to put it mildly, annoying.
type of selectivity is that which prevents the receiver from causing
interference to itself. Queer words, but true. If you get loud harmonics
from nearby ham stations or local broadcast stations, make sure that
they aren't being generated in your own receiver before telling the
other party his transmitter needs some things done to it. A straight
autodyne detector coupled to the antenna, and especially a receiver
with an untuned r.f. stage, may bring in lots of signals that actually
don't exist. A strong local signal will overload the detector or untuned
r.f. stage, which then will work as a frequency multiplier and generate
harmonics of its own. It would seem that we already have enough legitimate
interference without going to the trouble of manufacturing more of it.
Selectivity type number three has already been mentioned - the prevention
of spreading of moderately strong signals (or so-called "blocking" of
the detector) which not only makes them difficult to read but also wipes
out weaker signals nearby. This is simply a case of too much signal
at the detector. We have seen receivers in which this was so bad that
the use of a good-sized antenna when listening on the 3500-kc. band
at night was absolutely out of the question. All the signals blocked
the detector to such an extent that not a single one of them could be
All these things can and should be remedied in the 1933
autodyne receiver. If we can't get real "single-signal" performance
from the regenerative set we can at least get the next best thing to
it - elimination of practically all interference except that two-beat
tuning peculiar to the autodyne detector. Once this is done audio selectivity
will be of real help.
Eliminating Avoidable Interference
Harmonic generation in the receiver can be prevented or at least
made negligible by utilizing the selectivity offered by a tuned r.f.
stage. Since this type of interference occurs only when the interfering
signal is on a frequency which is at the most half of that of the desired
signals, a simple tuned circuit will be sufficient to keep out the fundamental
frequency of the interfering transmitter. If a harmonic remains in spite
of the tuned r.f. stage, then is the time to start blaming the transmitter.
The effectiveness of the tuned r.f. stage in cutting out interference
from local broadcast stations and nearby amateurs is also unquestioned.
Only on detector blocking do we have any quarrel with r.f. amplification.
And even this can be overcome by the simplest means imaginable - providing
the r.f. stage with a gain control so that a strong signal can be cut
down to the point where the detector does not block. An audio volume
control is helpless to do anything except keep the phones from rattling.
There are two obvious ways of controlling the r.f. gain of a receiver.
One is by controlling the signal input, which does not actually change
the gain but has an equivalent effect. When we cut down our receiving
antennas we are really reducing the signal input, but an antenna of
adjustable length would be a rather cumbersome affair. A method used
for years in certain broadcast receivers was to connect a potentiometer
between the antenna and ground and run the variable arm to the antenna
coil on the first r.f. transformer. The potentiometer acts as a voltage
divider and permits some regulation of the strength of the signal fed
to the r.f. tube. This method, although easy enough to apply, has its
disadvantages for ham-band receivers. In the first place, it brings
the r.f. right out to the panel, and in the second place the r.f. tube
is working its hardest even though the signal input is cut down. In
other words, although the signal has been weakened, the r.f. tube is
turning out just as much hiss as ever, making the signal-to-background
ratio even more unfavorable than it is normally.
A better method
is to vary the mutual conductance of the r.f. tube so that the actual
amplification of the stage is decreased when the gain control is turned
down. Then the tube noise will decrease in about the same ratio as the
signal strength, leaving it possible to copy weak signals. The actual
effect of this sort of gain control is to make an apparent improvement
in the signal-background ratio, because to the ear it seems as though
the noise decreases a great deal more than the signal does. The characteristics
of variable-mu tubes are ideally suited to this type of control. It
is only necessary to provide some means of varying the grid bias.
Simple though this may seem - and r.f. gain control really does
prevent detector blocking and enormously increases the effective selectivity
of the receiver - controlling the grid bias of the r.f. amplifier may
cause detuning of the detector circuit if the receiver is not properly
built. Inter-locking in tuning between r.f. and detector should be just
about eliminated to get full benefit of r.f. gain control, because if
there is regeneration in the r.f. stage the amount of it will depend
on the mutual conductance of the tube. Furthermore, the detector should
be a stable oscillator. These things mean good shielding and proper
choice of circuit constants. Before we tried the thing we anticipated
that the change in plate resistance of the r.f. tube with varying grid
bias might be the cause of an unavoidable change in the tuning of the
detector circuit, but experience has shown that detuning from this cause
is not noticeable at high frequencies. If detuning exists it can be
traced to remediable causes.
Getting away from selectivity for the moment, we've had a pet peeve
about regenerative detectors for a long time, especially regenerative
detectors in a.c. operated receivers. Most of them are far from being
stable-enough oscillators. The slightest change in plate voltage will
cause the beat note on a received signal to wobble around, a thing which
has driven a lot of amateurs to using "B" batteries for plate supply.
And when all a.c. supply is used, the way crystal-controlled signals
can develop wobbulation is something weird. Unfortunately no oscillator
working right on the ragged edge of oscillation, as a regenerative detector
does, can be wholly stable, but a lot can be done about it. And the
most effective thing to do is a stunt we have been using for years in
our transmitters - put some capacity in the tuned circuit. A detector
circuit with the largest possible coil and the smallest possible condenser
may give the greatest sensitivity, but then the frequency of oscillation
is also extremely sensitive to small changes in plate voltage - to say
nothing of its penchant for blocking or spreading out on any but weak
signals. All the trick circuits we have tried, including the so-called
separate regenerator tube, have failed to do a thing about this, but
a little dose of our old friend high-C helps amazingly. Maybe there
would be fewer plaints in our "Correspondence" columns about rotten
signals if more of us had receivers that would do justice to the many
really good ones on the air. Just as one example, a blindfolded observer
would swear that most of the hams in America had decided to reform in
the twinkling of an eye if he had a chance first to listen to the 40-meter
band on the kind of regenerative receivers most of us have and then
suddenly to be switched over to one with a really stable detector.
So far we have largely been talking generalities, but it should be evident
by this time that in our opinion the 1933 autodyne c.w. receiver should
have certain features. It should have a tuned r.f. stage, ganged with
the detector circuit of course for each tuning; it should have an r.f.
gain control to prevent detector blocking and increase the effective
selectivity; and it should have a detector circuit which is as stable
an oscillator as it is possible to make it. Its circuit diagram will
look pretty much the same as that of any other tuned-r.f. receiver.
The real difference will be in its performance.
Inside the Shields
Detector at the left, r.f. amplifier at the
right. The audio tube sits behind the drum dial in the rear left-
hand corner of the chassis. This photo shows the method of ganging
the midget tuning condensers.
These advantages have been incorporated insofar
as possible into the receiver shown in the photographs. Although five
controls have been brought out to the panel, the set is in reality a
single-control-tuning affair. The two upper knobs (provided with pointers)
are band-setting condensers; they are set when coils are changed and
need not be touched after that. In the lower right-hand corner is the
r.f. gain control. The regeneration control is diagonally below the
tuning dial; it, too, need be set only once when coils are changed,
since the detector will stay at the "just-oscillating" point over a
Fig. 1 - The Wiring Diagram
Heavy lines indicate grounds which should
be made at one point. Heaters (not shown) are wired in parallel. Type
39 and 37 tubes may be substituted for the 58's and 56 shown with no
change in the circuit diagram. Resistors R5 and R6
may be omitted if batteries are to be used as plate supply. See text.
All primaries (L1 and L3)
are wound with No. 36 d.s.c. wire. The 3500-kc. grid coils are wound
with No. 20 d.c.c.; 1750-kc. grid coils with No. 28 d.c.c.; both close-wound.
The 7000- and 14,000-kc. grid coils are wound with No. 18 enameled wire
spaced to occupy a length of 1¼ inches. Taps are from the grounded
end of detector coils. Coil diameters are 1½ inches.
To get a fairly high-C circuit for the detector, the parallel-condenser
method of band-spreading is used. This, as most of us know, consists
of using a fairly large constant capacity in parallel with a small variable
capacity. The degree of band spreading will depend upon the ratio of
the two capacities and the size of the inductance used for a particular
band. The circuit diagram is given in Fig. 1.
The panel is of
1/8-inch aluminum and measures 7 by 14 inches. The sub-base is made
of a single piece of 3/32-inch aluminum with the corners cut out and
edges bent down so that the top surface is 13 1/2 inches by 7 1/2 inches
and the vertical sides are about two inches high overall. The sides
were bent down with an ordinary small-size bench vise, first being scribed
on the under side along the bending line and then worked down to position
a little at a time. The two shield boxes are made of 1/16th-inch aluminum,
each measuring 4 3/4 inches high, 4 1/4 inches wide and 7 inches deep.
The panel constitutes the front of both boxes. The pieces making up
the sides of the boxes are fastened together by being screwed to vertical
pieces of 1/4-inch square brass rod which has been drilled and tapped
to take small machine screws at appropriate points. Similar rods are
also used for fastening the boxes to the panels. The lid fits over the
tops of both boxes and is held in place by small pieces of phosphor-bronze
spring strip which presses against the backs of the boxes when the lid
is put on.
Although working in aluminum may look difficult to
the ham with an ordinary cellar workshop, it requires more care and
patience than it does skill. All the work on this receiver was done
with nothing but a hacksaw, a bench vise, an ordinary hand drill, a
file, a ten-cent kitchen knife, and a few taps.
The tuning condensers
are 35-uufd. Hammarlund midgets, mounted on the left-hand side of each
shield box as shown in the top-view photograph of the set. This type
of condenser is readily adaptable to ganging because the shaft projects
about a quarter-inch beyond the rear bearing. The condensers should
be lined up carefully so the shafts and the center of the drum dial
are on the same line, to avoid twisting when the dial is turned. To
get a flexible coupling on the rear of the first condenser it is necessary
to take off the small spring contacts that wipe on the shaft by bending
them down and breaking them off. When this is done it is necessary to
make the contact to the rotor plates through the front bearing on the
condenser. The rear bearing does not fit tightly enough to make good
contact and the condenser will be noisy if an attempt is made to use
it. Leave the rear bearing unconnected. The two condensers are connected
together mechanically by two small flexible couplings (National) and
a piece of 1/4-inch round bakelite rod of appropriate length. A metal
rod could be used just as well. The dial is also connected to the first
condenser through the medium of a flexible coupling. When lined up properly
the whole assembly turns with surprising ease.
The two 100-uufd.
padding condensers, also Hammarlunds, are mounted on the panel in the
positions shown. The coil sockets (and the tube sockets as well) are
of Isolantite. These sockets are used not particularly because of any
electrical advantages but because they are mechanically rigid and will
stand the strain of changing coils without getting bent out of shape.
The coil sockets are mounted on small pillars of 1/4-inch metal tubing,
just long enough to allow the contacts under the sockets to clear the
base. The grid condenser and leak for the detector stage are held from
the base by a small metal pillar and are just behind the coil in the
Another photograph shows how the parts
are placed under the chassis. R.f. rather than artistic considerations
dictated the locations of the various parts. For example, there is only
one common ground connection for r.f. on the whole set; around it are
clustered all the .01 by-pass condensers in the r.f. circuits and all
the other r.f. grounds come to this same point. Resistors and audio
condensers are mounted wherever it is most convenient to put them, especially
if the pigtails provided on them can be used. Occasionally there is
an insulating terminal made by riveting a soldering lug to a small piece
of fiber which in turn is fastened to the base.
The audio choke,
a small audio transformer made for broadcast replacement purposes, is
mounted on the edge of the chassis at the right. Its primary and secondary
are connected in series. This particular transformer has a rather definite
peak in the vicinity of 1000 cycles and, as a result, contributes a
little audio selectivity to the set.
There is little more to
be said about the mechanical arrangement of the set. The tuning dial
is placed on the left because it is convenient to be able to tune the
receiver without getting in the way of copy paper and log books and
leave the right hand of the operator free. If you're left-handed, modify
the layout to put the dial on the right-hand side. The regeneration
control knob is near the tuning knob so both can be worked with one
hand conveniently, although not simultaneously.
A few electrical pointers should be of help, especially to those who
have not previously attempted to build a regenerative receiver with
a tuned r.f. stage. Don't try to build a shield for the r.f. and detector
stages with a single partition between the two compartments. A common
partition, instead of acting as a shield, actually will couple the two
circuits together. As a result the r.f. stage will break into oscillation
whenever it is tuned to resonance with the detector. This is not theory;
we tried it that way first. Separate boxes, as shown in the photograph,
not only stopped the oscillation but also took out practically all tendency
toward interlocking of tuning in the two stages on all but the highest
Informal - but Effective
A view underneath the base. No particular
precautions here except to keep r.f. leads short and all r.f. grounds
at one point.
As has been mentioned before, all the r.f. grounds
in the set come to a single point. Not only that, all parts of the r.f.
circuits that of necessity are connected to the panel or chassis at
different points - such, for instance, as the connections made by mounting
the tuning condensers - are also connected to the common ground through
copper wires. No dependence should be placed on contacts to aluminum
The circuit used for the detector differs a little in
this receiver from the ordinary tickler circuit. It was used because
we felt it desirable to use 5-prong coil forms, and in order to use
magnetic coupling between the r.f. stage and detector it was necessary
to use an oscillating circuit which requires only three connections.
The circuit is a Hartley, using the screen and plate in parallel as
the anode and having the cathode tapped up on the coil for regeneration.
It somewhat resembles the electron-coupled oscillator - several suggestions
for this type of circuit have been received from different amateurs
and are described in the Experimenters' Section in this issue - but
so far as can be told from ordinary observation its performance is not
greatly different from the ordinary regenerative circuit. It is used
here largely as a matter of convenience. If 6-prong coil forms are available,
the use of the regular tickler circuit is recommended, because then
condenser regeneration control, which has much less tuning effect than
screen-grid voltage control, can be used. Condenser control does not
work with this circuit because the plate and screen are in parallel
for r.f., and even if there is no by-pass capacity from one to the ground,
the other will take charge and keep the detector oscillating; hence
the screen-grid voltage control shown in Fig. 1.
The band spread
with the variable condensers specified in Fig. 1 is not "full-dial"
on any band, running about 60 degrees (100-division dial) on 3.5 mc.,
40 degrees on 7 mc., and 25 degrees on 14 mc. More spread can be obtained
by using a smaller tuning condenser. The Hammarlund 3-plate, with a
maximum capacity of 20-µµfd., will widen out the bands considerably.
Personally we do not care for the larger spread for a receiver with
ordinary selectivity because cranking a high-ratio vernier dial over
its whole scale to cover a band is a rather lengthy and laborious operation.
This is a matter of individual preference, however. Changing to the
smaller tuning condensers will not affect the sizes of the coils nor
make any changes in the other circuit values.
The Hartley circuit
in the detector is a facile oscillator; so much so that the "tickler"
- we might call that part of the coil between ground and the cathode
tap the tickler - is matter of fractions of turns on the high- frequency
bands. The right place for the tap has to be hunted out if the detector
is to be controllable with a reasonable value of screen voltage. In
this particular set the tap is three turns from ground on 1.75 mc.,
one turn on 3.5-mc., 1/2 turn on 7 mc. and 1/4 turn on 14 mc.! The taps
are made by boring a small hole in the form alongside the point where
the tap is to be placed, running a wire through the hole to the pin
on the coil form, and soldering to the turn on the coil. All the coils
should be "doped" with collodion or a similar material. The 1.75- and
3.5-mc. coils are wound with d.c.c. wire with no spacing between turns;
the 7- and 14-mc. coils are wound with enameled wire to the length specified
in Fig. 1, spaced out by hand and then doped to hold the turns in place.
A fairly even job can be made when the coil has a dozen or less turns.
With coils of the sizes specified, the amateur bands will be located
with the padding or band-spreading condensers set near maximum on the
7- and 14-mc. bands, and at about 1/3 capacity on 3.5 and 1.75 mc. There
will be no need for cut and try if the coil specifications are followed;
this band-spread system is an easy one to get into operation because
slight variations in coils can be compensated for by the condenser settings.
Once the right settings of the padding condensers have been determined
for all bands appropriate marks can be put on the panel or small paper
or metal scales can be made up and calibrated. Setting the padding condensers
is not by any means a hair-line adjustment unless it is necessary to
have exactly the same dial readings every time one returns to a band.
This is a receiver, however, not a frequency meter.
on the r.f. coils run about as with other sets. The primaries for the
detector coils are not critical as to number of turns; the values specified
give plenty of gain and cause no undue interlocking of tuning. Primaries
are close-wound at the bottoms of the coil forms, grid coils at the
Strictly speaking, the r.f. gain control is not a volume
control and it will not reduce all signals to zero strength, since with
only one r.f. stage the range of control is limited. Actually, however,
it controls volume nicely even though complete cut-off is not obtainable.
The purpose of the resistor R4 in Fig. 1 is to increase the
range of control over that available by the use of R3 alone
in the cathode circuit. With R4 connected as shown, there
is a voltage drop across R3, because of voltage divider action,
which acts in addition to the normal drop caused by plate-current flow.
The total bias with all of R3 included in the circuit is
in the neighborhood of 50 volts.
A voltage divider consisting
of a pair of small resistors (5-watt size) is included in the receiver
so that only two plate leads, plus and minus 200 volts, leave the set.
The filaments of the tubes are wired in parallel and are brought out
to the power supply through another pair of leads, making only a 4-wire
cable necessary. The center-tapped resistor across the filament supply
should be included in the power pack. This arrangement, which is used
by National in their a.c. short-wave receivers, has been found very
effective in keeping r.f. out of the power supply cable and in eliminating
hum caused by stray r.f. wanderings.
If batteries are to be used
for plate supply, resistors R5 and R6 can be omitted
and a separate lead brought out for the regeneration control. There
should be a switch in the negative battery lead to cut off the current
drained through R4. and R10 when the set is not
The antenna input on the set is arranged so that
a doublet antenna can be used, both terminals on the antenna coupling
coil being brought out to binding posts which are insulated from the
chassis. The ground post is connected to the common r.f. ground. To
use the ordinary antenna-ground connection one of the antenna posts
is connected to the ground post and the other used for the antenna.
More doublet antennas should be used, however. They improve the signal-noise
ratio considerably, as has been pointed out in QST several times, besides
doing a better job of picking up DX signals than the 10-foot indoor
antennas that many of us use. A good antenna is worth more than an r.f.
stage in bringing up signal strength, and it seems rather silly to build
a receiver with an r.f. stage and then cut the antenna down to the point
where the signals are the same as they would have been with just the
detector and a decent antenna - simply because the gain has not been
How it Works
A word about
the performance of this receiver. On all but 14 mc. the tuning of the
r.f. stage and detector are almost completely independent; that is,
the r.f. stage can be swung through resonance without causing more than
a slight change of beat note on a received signal and without affecting
detector oscillation. The 14-mc. band does not do quite as well, but
even here the interlocking is not as bad as on most of the tuned r.f.
receivers we have seen. The gain control does not affect the detector
tuning so long as it causes no change in the voltage applied to the
detector plate; in other words, with battery supply the gain control
would be entirely independent of frequency. With a conventional a.c.
plate supply in which no attempt has been made to improve the voltage
regulation there will be a slight frequency change in the beat note
of a received signal, its magnitude depending upon the extent to which
the plate voltage changes when the gain control is operated. The gain
control changes the plate and screen-grid current of the r.f. tube from
a maximum of something like 11 milliamperes down almost to zero, and
with the particular power pack used in testing the receiver this difference
in load caused the plate voltage on the detector to swing something
like 15 volts - enough to cause a perceptible frequency change even
though the circuits are fairly high-C. Some neon-bulb voltage regulation
evidently would be in order.2 The frequency change is rarely
bothersome, however, because the gain control usually is set for a level
which gives desirable volume and then left alone.
The set as
it stands is not perfect, of course; nothing ever is. It is a real pleasure,
however, to operate a receiver in which the detector does not block,
and on which the signals stay put despite normal variations in the power
line voltage. It is satisfying to be able to work distant stations almost
within beat note of a local ham station. And it is even more satisfying
to be able to use a decent-sized receiving antenna and know that when
it is necessary to go after the weak fellows the r.f. gain is there
and the antenna will be big enough to do some good.
1 "What's Wrong With Our C. W. Receivers,"
J. J. Lamb, QST, June, 1932.
2 "Stabilized B Supply for
the A.C. Receiver," Dekker and Keeman, QST, October, 1932.