I wax nostalgic about old tube radio sets, it is not because I don't
appreciate the performance and quality of modern electronics. It
is just that a lot of the technology was still mainstream when I
was young (born in 1958). I remember having it in my parents' house
and seeing even older stuff in my grandparents' house. Some people's
midlife crisis takes the form of wearing age-inappropriate clothing,
gold jewelry, and chasing after strange women. The manifestation
of my 'crisis,' if you want to call it that, has been collecting
memorabilia from days of yore. There is a huge demand for it, so
I make as much as I have time for posting available for others to
enjoy. Articles like this one are from old editions I bought on
eBay, a 1963 edition of American Modeler in this instance. Even
though nobody will go out and buy parts to build this tube-based
R/C transmitter, there are useful descriptions of circuit design
considerations, including the use of a center-loaded, half-wave
antenna. Hams eat this stuff up. Enjoy.
"Handy-Mac" 50-mc R/C
Our radio control advisor finally ROG's (rises-off-the-ground) with
a potent, hand-held transmitter guaranteed to make any properly
tuned receiver behave 100% good like a receiving set should!
By Howard G. McEntee
Efficient antenna and output stage assures good power from this
hand-held 50-mc R/C transmitter, yet you get reasonable operating
time from each battery charge. It's suitable for Kickin' Duck, Galloping
Ghost and other pulse rate and length control systems. A deluxe
outfit, yes - but advanced modelers can pick out the features best
suited for their own use. The RF section is fine for tone or CW
receivers, the modulator is stable enough for reed or filter use,
the pulser is adjustable for practically any need.
Engraved name plate adds class!
Antenna slides into insulated tube.
Black blob is taped pack of nickel-cads.
Underside of RF chassis.
RF chassis top, note clamp holding crystal.
Bottom of pulser/modulator
Pulser/mod topside, all tubes use shields.
Loading coil modification.
long felt the need to be freed from the physical restrictions of
a ground type transmitter, Handy-Mac was in the planning stage for
several years. Our philosophy calls for a rather potent transmitter
(which includes an efficient antenna system) and fairly insensitive
receiver (mainly to reduce troubles from interference due both to
other transmitters, and to "electrical noise" generated in the plane)
so prime design goal here was lots of signal out in the air. A "straight-through"
final amplifier with a tube designed for RF use at these frequencies,
and a center-loaded antenna were considered basic. Also, a power
supply capable of relatively high voltage was a necessity.
Planned at the start was a nickel-cad battery, and a transistor
converter. Then there were plenty of ABC #2 nickel-cad cells available,
and the case was chosen to allow six of these to fit snugly across
the back. These cells are now rare, but six of the ABC #1 cells
can be squeezed in; or, six of the much higher but thinner surplus
cells of the type sold by Esse Radio can also be adapted. All these
cells seem to be rated around 5AH capacity, and all would give fine
results. However, about a year ago the 4AH sintered plate nickel-cad
sealed cells were announced by Gould, and the advantages of the
sealed cells were worth making design changes to accommodate. These
cells are very clean, never have to be filled, are much smaller
and lighter than the surplus plastic-case cells (they are the same
size as D flashlight cells). They will stand the current drain of
the transmitter with no trouble at all, and have proven ideal for
this application. With the surplus cells we had intended to mount
the battery and the converter on the rear of the case; use of the
Gould 4.OSC cells allowed everything to be mounted in the main portion
of the case.
The case itself is "special," in that it is
the only one we know of which is made in the manner you can see
in the photos (front, two sides and one end are all in the main
unit). It is of .050 aluminum, and thus rugged enough to withstand
the beating field equipment like this takes. The case can be had
in plain aluminum or gray paint; we chose the former, since it reflects
heat much better (glow fuel soon makes painted cases look crummy).
The case was gone over with very fine emery paper to give it a "grain,"
then was given an alkaline etching followed by clear anodizing.
The latter two processes were done commercially, cost $4. Anodizing
is a very hard tough finish, helps prevent all the little scratches
that soon mar soft aluminum surfaces.
It was decided
at the outset that since we would probably be using this transmitter
for quite a number of years (the old Mac-50, which was forced into
semi-retirement by the Handy-Mac, was in constant use for about
10 years) the various components would be made up in sections which
could be removed fairly easily, and replaced, when new ideas came
along. Thus, the RF section has its own chassis, and there is another
for the modulator and pulser. Power supply components are easily
Since we were after lots of RF efficiency,
one of the most efficient tubes we know for the output amplifier
is the 3B4. It has another asset we make use of-a designed filament
voltage of around 1.25 volts. It's undoubtedly true that a single
nickel-cad cell on the filaments of tubes intended for use with
regular dry cells (such tubes have a "design center" voltage rating
of 1.4, will give good results over a range of perhaps 1.3 to 1.5
volts) results in at least shorter life and definitely lower output.
This is especially so when the tube is being run up near its maximum
current ratings. Our 3B4 is really just loafing, and is getting
a voltage it's designed for, even when the filament cell sags down
a bit as the charge is dissipated. All the other tubes in the transmitter
are operated at much below maximum current ratings - which is how
we justify operating them on a single nickel-cad cell too.
Some tries were made at using 50-mc crystals, with just an oscillator
at this frequency feeding the 3B4 amplifier. While good output could
be had, everything had to be run right on the upper edge, and it
just didn't look too practical. So we fell back on the old faithful
3A5 as 26-mc oscillator and doubler, to feed the 3B4. Thus the circuit
is very much like the Mac-50, but we did use a simpler and neater
neutralizing circuit, and slug-tuning for the doubler.
Since a transmitter of this complexity won't be tackled by beginners,
we are skipping exact cutting details for the case, chassis and
other parts. The photos show where parts are mounted, and the more
experienced builder will doubtless want to use parts he has on hand,
which might require some shifting back and forth.
The transmitter chassis is L-shaped, attaches to the front and the
side of the case. In the underside view, note all parts which project
under the chassis are mounted along one edge. This allows clearance
for the antenna, which collapses almost completely into the case.
Only item along that side of the chassis is a lug strip, which carries
most of the resistors. No commercial strip could be found to fit
out specs, so one was made, using a 3/8" wide strip of 1/16" thick
fiberglass epoxy sheet; lugs are rivet type (Ace #ELI are suitable).
L4 and L5 are supported by their tuning capacitors,
which have slotted shafts; tuning is through holes in front panel;
to guide screw driver to slots, lengths of phenolic tubing are fitted
in holes and run back over the stub capacitor shafts. Tubing also
prevents shorts and "fireworks" if non-insulated screwdriver is
All tubes in the transmitter are mounted in
sockets which have detachable shields. The crystal socket is fitted
with a spring clip, which holds the crystal firmly but allows easy
It will be seen on the RF unit circuit that
a switch is used to shift the single meter to various places, for
monitoring current - and voltage. SW4 does this, is considerably
larger than we had figured on, and had to be squeezed in. In case
some readers spot the Lafayette SW-78 as an ideal choice for this
spot, (as we did) don't use it; it is a shorting type, not suited
for this purpose. The larger Mallory unit can be fitted in with
A lug strip was mounted at lower edge of each chassis,
to make for easier attachment and removal of power leads. Since
most of the leads to SW4 come from the RF chassis, this switch is
wired to the chassis and has to be removed with it.
about that collapsible antenna? It is a center-loaded type, can
be used just as it comes (though we made a slight modification,
see sketch) and gives us the advantages of a full half wave radiator
- not the more usual quarter wave. One of these advantages is that
the case of the transmitter is "stone cold" RF-wise. With the usual
quarter wave antenna, the case, the operator and even the ground
he stands on are all part of the overall antenna system. If all
are matched up right and the transmitter is tuned to match also,
the antenna will put out well. But difference between such factors
as dry or wet hands (moist or dry atmosphere) can make quite a difference
(Right here someone is bound to bring up the
point that many thousands of commercial HH transmitters with such
antennas have - and do - work fine. Agreed, but the aim was to make
the Handy-Mac antenna system even better).
half wave antenna is complete unto itself - it doesn't depend upon
the operator's shaking arms for part of its "circuit." Anyhow, by
proper selection of parts and correct tuning, we have been able
to reduce the RF on the case to practically zero; the transmitter
will show almost exactly the same FSM reading when hand held, placed
on the ground or up on a wooden table. Also, the amplifier plate
current doesn't change appreciably under these different conditions.
No really exact comparisons have been made, but FSM and other checks
with transmitters having about the same input to the final amplifier
show much greater output for the Handy-Mac. Part of this may come
from the highly efficient RF amplifier - but part undoubtedly also
comes from the antenna.
We were able to locate a commercial
antenna that is almost exactly what is required - a German unit
made by Graupner, and intended for use on the overseas 40-mc R/C
spot. Due to the loading coil, this antenna is considered quite
a "custom" unit, and costs considerably more than the plain types,
around $6. We feel it is well worth the cost, especially in view
of the fact it collapses almost entirely into the transmitter. Only
2 1/4" projects above the top. You can never forget your antenna
with this type, and you don't have the nuisance of detaching it,
when the transmitter is not in use. For those who get this particular
unit, note that the section just above the loading coil pulls out
very easily, up to the last 1 1/2"; be sure you get it all the way
out, or the loading coil will be shorted.
make sure the bare antenna doesn't short anything when it is collapsed,
we fitted a phenolic tube (this comes from another antenna sold
by Polks) for it to slide into. The modification mentioned earlier
is shown on the drawing, which also gives rough measurements for
those 50-mc R/Cers who want to try making their own center-loaded
job from other parts. We found the final antenna, suspended from
the ceiling and with 2" lead soldered to lug on mounting (this lead
attaches to C5, when antenna is on case) resonated at about 49 mc
with a grid dip meter.
An output monitoring circuit
is built into the transmitter, the antenna of which is the handle
atop the case. This handle is a type sold for kitchen cabinets,
comes with a couple of decorative plastic "insulators." A spring
is mounted to contact one of the handle screws when the cover is
in place; then with the meter switch on terminals F-G, actual RF
output can be monitored. The reading drops way down when the handle
is not in the circuit.
few notes on the meter switching circuits. Switched to A-D, oscillator
plate current may be measured, R1 being chosen to shunt the normal
1-ma meter up to 10-ma. Shunts will have to be selected to match
the meter you employ; for the specified meter, about 9.1-ohms did
the job. Next meter switch position puts it across R2; this gives
grid current of the 3B4, with the 1-ma meter reading a few percent
low, due to shunting effect of R2; R3 is selected to shunt the meter
to 30-ma, for amplifier plate current. Switch SW4 terminals H-C
connect the meter across five cells of the power supply - those
that drive the DC converter. Since drain on these cells is a little
heavier than that on the filament cell, it was felt the latter did
not need metering.
With only a single cell for filaments,
every effort must be made to keep voltage drops in the filament
circuit as low as possible. This means all filament leads should
be of heavy wire (#12 stranded was used here). To raise total drain
on the filament cell to near that of the cells driving the converter,
a rather heavy drain pilot lamp is employed. We found a G.E. #123
about right; it is rated at 1 1/4 volts and 0.3=A.
seen the destruction that can be caused in a transmitter when there
is a short on the nickel-cad power supply, fuses were fitted in
both battery circuits.
The Gould cells have solder lugs
for intercell connections, are taped up into a solid package and
held in the case with an aluminum strap. We took a tap off every
cell, and these all run to the 7-pin socket on front of the case.
The end terminals are used for charging. A voltmeter can be connected
across each individual cell, for monitoring voltage.
found the Diem converter could be attached to the case side below
the audio and pulser chassis. This converter was chosen because
it has two separate output voltages, high for the RF circuits and
modulator, and another output of 45-volts for the pulser. The converter
is a type originally intended for TTPW transmitters and ideal for
When laid out at the beginning, there was no
intention of fitting pulse rate and length trim controls, and no
room was left for them. Thus, a final decision to include these
controls found us with no room for standard size dual pots, and
holes had already been drilled in the front of the case for all
switches etc. On hand were a couple of special Centralab dual pots
of 5/8" diameter, and these were pressed into service. If trim pots
are planned on from the beginning, the more standard size duals
could easily be fitted on the case front. To assure maximum space
behind them for the converter and battery, panel switches should
have shortest possible "neck" and be of type with lugs projecting
from ends, rather than rearward.
The pulser is a rather
conventional multi-vibrator, very much like the original WAG type
using a pair of 3V4's. A number of variable adjustments were included,
to make it possible to "tune" the pulser to an existing plane fitted
with Kickin' Duck, or for any other control system likely to be
tried. Thus, in addition to pulse length trim (R6) and Rate trim
(R10) there are pots for high pulse rate setting (R9), low pulse
setting (R12) and two more (R8 and R9) that have been found useful
in the Kickin' Duck system (see article in A.M., Sept. '61).
The main pulse length and rate pots, R7 and R11 are of special
type giving full resistance change in only about 60 degrees of.
shaft rotation. The compact control stick assembly is shown in some
detail, utilizes "clothespin" type springs for positive centering.
Adjustable stops are built in, but some builders prefer just to
let the edge of the case opening, through which the shaft protrudes
act as a "stop." Resistors R8 ride on the back end of control stick
assembly held by a small phenolic plate. Main problem with control
stick mounting of this sort is to arrange the leads from R7 so they
are free to move as the stick is varied, but so they won't rub on
other parts or break at the ends.
Since space is at
a premium, a slot had to be cut in the modulator chassis to accommodate
R11. On this chassis, the two 3V4 tubes are at bottom, 3A5 modulator
above them, and stabilizing inductor L8 at top. The pulser relay
is what is generally known as the "Bramco" type, has armature contact
insulated from relay frame. This may have to be procured direct
from Jaidinger Mfg, Co.; we obtained palladium bar contacts, as
silver pulser relay contacts in this circuit have not been found
to stand up too well.
Since the writer is left-handed,
the transmitter is cradled in the right arm, with fingers wrapped
around the left side of the case (viewed from front) and the On
and Off buttons are on that side. R5, which varies the modulator
tone somewhat, may be seen alongside L8.
a receiver now in use, the modulator components were chosen to produce
a tone variable from about 2,000 to 2,600 cycles. 100% modulation
is provided. For info on this type of modulation, see article in
A.M. (Oct. '59
We won't go here into the matter
of balancing parts for the pulser, as this has been well covered
in past issues of this magazine. For more info, look up references
listed in articles on Kickin' Duck (A.M., Sept. '61; '58 Air Trails
To keep dirt out of the interior, a leather
"boot" cut from a discarded suede glove is attached to the control
stick, with edges held by an aluminum "frame."
on the front panel are cut from special R/C decal sheet supplied
by Ace, and each cutout is given several coats of Lee's Shield,
as protection from the inevitable glow fuel smeared fingers that
will be handling the outfit. The sharp looking name plate at bottom
of the case front is an etched job provided by a friend.
Now, about tune-up, operating values. As far as the former goes,
we feel the experienced ham will know how to go about it. The oscillator
circuit has just a slight amount of regeneration, and fairly peppy
crystals should be used. Those specified in the Parts List have
been found suitable; other good makes may do as well. After getting
the oscillator and doubler tuned up, and a good grid current reading
on the 3B4, this tube should be carefully neutralized, The set will
work with no neutralization - but it's much more stable and easy
to tune with it. Furthermore, we are strongly of the opinion that
many cases of "insufficient modulation," "modulation percentage
too low," and even of "receivers that overload badly close to the
transmitter" are due entirely to leakage of RF power through a final
amplifier tube that is not neutralized (and from these angles it
is just as important to neutralize a doubler used to feed the antenna,
as it is a "straight through" power amplifier - anyhow, do a careful
The coupling coil L5 must be placed to
load the 3B4 as desired; C2 is used to adjust tuning, after L5 has
been set roughly, and if latter is right, you will be able to get
proper loading at two settings of C2. In other words, L4 and L5
are a little over-coupled, then the antenna circuit is detuned slightly
to adjust coupling so the 3B4 plate current is just what you want.
With properly adjusted antenna coupling, fully charged
set of nickel-cad cells, current and voltage values in the outfit
are about like this (modulator and pulser off): high voltage, 166;
pulser voltage, 44; oscillator plate current, 6.5-ma; doubler current,
7-ma; 3B4 grid current, 0.75-ma; 3B4 screen grid current, 4-ma,
3B4 plate current, 15-ma (antenna coupling adjusted to obtain this
value). This indicates a plate input to the 3B4 of about 2.48W,
and power output was measured at 1.4W, showing a plate efficiency
of some 56 1/2% - considered very high for an RF unit of this sort.
The 3B4 plate current drops somewhat with modulation, as is usual
with the, sort of grid modulation used here, so that even though
the modulator takes about 4 ma total, when the tone is on, the drop
in 3B4 plate current is about the same, and overall current drain
stays about the same as without modulation, The pulser also draws
about 4-ma (at its 44-volt level) and there is about 2.4-ma through
the 7,500-ohm relay. The relay is set to operate at 2-ma and release
at 1.3-ma. With fully charged batteries, drain on the converter
supply is some 1.2A, and about 1.05A on the filament cell. When
SW3 is opened, 3B4 plate current is only about 3-ma; this is still
a potent signal close by, but for shop use we collapse the antenna
fully (while this detunes both antenna and 3B4 plate circuit, current
in latter stays roughly the same as with antenna extended). This
holds true even with full power, so the transmitter can be used
for shop or close range testing with antenna collapsed, with no
Flight tests have shown the transmitter
really puts out. As expected, the signal is not as strong at a distance,
and especially with plane on the ground, as with the old Mac-50.
But that is a pretty potent powerhouse; while the 3B4 in the Mac-50
runs at almost the same input as it does in the Handy-Mac, the full
length half wave antenna on the former is undeniably much more efficient,
Even to one accustomed to a very peppy ground based transmitter,
we feel the new HH job will prove highly satisfactory.
RF and Power Sections
Control Stick Mechanism Is Shown Actual Size
Listed are the most
specialized units in transmitter; many which are standard are not
included. All resistors are 1/2W carbon. R1, 100 and 10-ohm carbon
in parallel; R3, 3.3 and 33-ohms in parallel; R4, 10K (these three
must match particular meter used); R5, 100K, Mallory 1/2" dia. (Lafayette
VC 536); R6, dual linear 250K (see text); R7, special 1-meg linear
(Ace 60 degree type); R8, both 5-meg (CRL type B16-128, knobs removed);
R9, 200K, Mallory 1/2" dia. (Laf. VC 537); R10, dual 10K (see text);
R11, special 100K linear (Ace 60 deg. type); R12, 50K Mallory 1/2"
dia. (Laf. VC 535). C1, C2, 15-mmf APC type (Laf. HP-10); C3, 1-7-mmf
CRL ceramic trimmer (Laf. CA-375); C4, C5, .25-mf tubular paper
sub-min (Ace "Aerolite"); all capacitors in modulator, all those
in RF section except .01-mf should be low temp. coefficient ceramic.
SW1, SW2, SW3, toggle sw., lugs on ends; SW4, Mallory 2 pole, 5
pos. non-shorting rotary (Laf. SW-367); SW5, NC push button (Grayhill
30-2); SW6, NO push button (Grayhill 30-1). F, dual fuse holder,
3-A fuses (Laf. EI 373 and EL 230 fuses). All sockets and shields,
Elco (Laf. MS 495 and MS 499). Case, LMB type EL 1063, 10 x 6 x
3 1/2" (Newark Electronics, Chicago). Crystal, Ace 26 mc, Int. Crystal
25.5 and 26.5 mc units have been used here. L1, type LS6 1/4" dia.
ceramic coil form, 10T, #26E wire, red dot core; L2, same form,
white core, 10T #26E (Ace forms used); L3, 22-uh RFC (Gyro); L4,
9T #14, 1/2" ID, 1" long; L5, 7 1/2T #18E, 1/2" ID, close-wound,
3/8" from L4; L6, part of Graupner antenna (Polk's); L7, 70-uh RFC
(Gyro); L8, Gyro T9643 AF choke. All tubes, Gyro. Meter, sealed
1-ma, 1 3/4" sq. (Gyro model HS 1).
Posted December 15, 2012