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Rationalizing the Autodyne
January 1933, QST
Although 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 (visit ARRL
for info). All copyrights hereby acknowledged.
Rationalizing the Autodyne
A Three-Tube Regenerative Receiver of Unusual Performance
By 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 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 real service.
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
Band-setting condensers 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.
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.
A 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.
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
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.
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
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
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.
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 band.
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.
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
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.
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.
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
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 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.
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.
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.
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.
"What's Wrong With Our C. W. Receivers," J. J. Lamb, QST, June, 1932.
"Stabilized B Supply for the A.C. Receiver," Dekker and Keeman, QST, October, 1932.