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.
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. As time permits, I will
be glad to scan articles for you. All copyrights (if any) are 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
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.
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.
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
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
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.
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
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
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. 1.
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 detector compartment.
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.
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
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
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.
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.