Rationalizing the Autodyne
January 1933, QST
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 has.
January 1933 QST
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
A Three-Tube Regenerative Receiver of Unusual Performance
By George Grammer, Assistant Technical Editor
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 predecessors.
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
Where R.F. Amplifiers Fail
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.
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.
second 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 copied.
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.
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
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
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
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
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.
A Practical Receiver
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 whole
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.
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 detector compartment.
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.
Some Helpful Hints
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 frequencies.
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 for r.f.
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
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
Antenna windings 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 top.
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 in operation.
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 controllable.
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.
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.