[Table of Contents]People old and young enjoy waxing nostalgic about
and learning some of the history of early electronics. Popular Electronics was published from October 1954 through April 1985. All copyrights (if any) are hereby acknowledged.
Cafe visitor David M. wrote to ask that I scan and post this article
from the January 1963 edition of Popular Electronics. It is an article
written by Philip Hatfield, of the Receiving Tube Department of General
Electric that describe a very simple design that uses a "compactron
vacuum tube, which consist of two triodes and a pentode. The compactron
was sort of a vacuum tube version of the multi-amplifier integrated
circuit of today. They are still available for purchase on eBay for
a couple bucks each.
See all articles from
One Receiver, All Bands
thanks to plug-in coils...
By Philip E. Hatfield,
Receiving Tube Dept., General Electric Co., Owensboro, Ky.
of today's short-wave receivers are truly sensitive and reliable devices,
but they are also rather complex and expensive for the beginner to construct.
Here's a simple receiver, using one compactron tube, that will give
you long-wave, broadcast-band, and short-wave reception. If you are
considering putting your first receiver together, this one is for you.
If you, have an amateur-band-only receiver, this unit will fill in some
of the "holes" in the spectrum. Finally, if you already have a general-coverage
receiver, this set will make a good "auxiliary" to tuck a way on a corner
of the desk just in, case your "big" one quits.
Use of a compactron
allows a lot of receiver to be contained in a small box without undue
crowding. the frequency range covered is from 250 kc. all the way to
16 mc.; and, since plug-in coils are used, it's possible to extend the
range in either direction. Plenty of headphone volume is provided, and
many signals will operate the built-in speaker in a very satisfactory
The Circuit. The 6AF11 compactron contains
two triodes and a pentode. One triode is used a regenerative detector,
the other as an audio voltage amplifier, and the pentode as an audio
Plug-in coils containing primary (L1), secondary
(L2), and tickler (L3) windings determine the frequency range. Tuning
is done with a relatively large variable capacitor (C2) to allow covering
a wide range of frequencies with a minimum of coils. For fine tuning,
a small variable capacitor (C3) is connected in parallel with the larger
one to act as a "vernier."
The antenna coupling circuit is purposely
designed for versatility. Straight inductive coupling, series tuning,
or parallel tuning are possible, depending on the connections to jacks
J1, J2, and J3 (see antenna hookup diagram). This can be quite helpful
in increasing the selectivity of the receiver and in tuning out the
"dead spots" that afflict most regenerative receivers.
audio output, the headphones are operated from the pentode section of
the compactron, and the phone jack (J4) is arranged to disconnect the
speaker when the phones are in use.
is the word on antenna hookups for this receiver, and three possible
configurations are shown.
All parts of the receiver, with the exception
of the spare-coil rack, and the trap door for coil changing, are mounted
on the portion of the chassis box used to form the front panel and sides.
As the photos show, this makes all parts of the receiver readily accessible
to the builder. In addition, since no electrical components are mounted
on the removable portion of the box, all the testing that is necessary
can be done before the cabinet is "buttoned up."
To reduce sheet
metal bending to a minimum, the chassis proper is a fiat plate, cut
to make a fairly snug fit, and then fastened in place with four small
angle brackets. All mounting holes should be cut in this plate and the
chassis box before the plate is bolted in place.
holes have been drilled, all of the parts should be mounted, since they
are all readily accessible for wiring in any sequence. In mounting the
40 p.p.f. antenna tuning capacitor (C1), flat washers should be
used between the panel and the capacitor frame to insure that the screws
don't extend through the frame far enough to interfere with the rotor.
Wiring of the receiver isn't especially critical, and the receiver
is compact enough to allow component leads to furnish many of the connections.
However, be careful to wire the coil socket exactly as shown, since
proper wiring here is just as important as on the tube socket.
Chassis Assembly Wiring Drawing
The Power Supply.
A separate entity, the power
supply is built on a 5" x 2¼" x 2¼" chassis box. Holes
for the various parts should be drilled in the box and all parts mounted
before any wiring is done. Again, the wiring isn't critical, although
care should be taken in connecting leads to the output socket (J5) to
make sure that the proper socket contacts are used.
No likelihood of losing coils with this set - one inserted through
a trap door is always in use.
The other three rest in empty sockets mounted on aluminum flange
at rear of cabinet.
The power cable which connects the power supply to the receiver is made
from a length of five-conductor, plastic-covered cable. This cable allows
the power supply to be placed in some convenient spot away from the
receiver. If the plastic-covered cable isn't available, individual stranded
insulated wires can be used to make the cable, with bands of tape fastened
at intervals to keep it together. Be sure that the wires used for the
heaters are at least #20 gauge. Before testing the receiver, double-check
to see that all of the plugs and sockets are correctly wired so that
the voltages January, 1963 from the power supply arrive at the right
points in the receiver. The Coils.
receiver can be tested, at least one of the plug-in coils must be wound.
Start with the broadcast coil, since it covers the range where results
are easiest to obtain.
The polystyrene forms will call for some
cautious handling-when drilling, too much pressure may crack them; and,
when soldering, excessive heat will soften them. Lightly filing the
ends of the coil form pins to remove the plating will make soldering
easier. Remember, rapid soldering is required to prevent softening
of the form. Start by winding the primary, followed by the secondary,
and then the tickler.
One way to make a neat job is to push
the wire through the starting hole in the form and into the pin and
then solder it in place. Then unwind the amount of wire from the spool
that you think will be required, but don't cut the wire just yet. Instead,
clamp the spool in a vise and walk away until the wire is under slight
Wind the coil by turning the coil form in your hands
as you walk slowly toward the vise. If you have underestimated the wire
needed, or if your workshop is small, hold the coil in one hand to prevent
the wire from slipping, remove the spool from the vise, unwind more
wire, re-clamp the spool, and continue winding. If you take your time,
you should have a professional-looking winding job with the wire tightly
wound and uniformly spaced.
When the proper number of turns has
been wound on, cut off the wire (leaving a lead of about 6/1) , put
the wire through the proper hole in the form, place your thumb over
the hole to hold the wire in place, remove the insulation from the wire,
push the wire through the proper base pin, and solder it in place.
Incidentally, it's especially important that the secondary and
tickler coils (L2 and L3, respectively) be wound in the same direction.
If they're not, the regenerative detector won't operate properly. In
the event that you experience trouble in getting the set to oscillate,
try reversing connections to either L2 or L3 - not both!
information on the other coils is given below, it will probably be better
for you to skip over to the "Operation" section at right, read that
material, and try the receiver. Then you can come back and wind the
other coils. Three of the coils are single-layer affairs, and are all
wound in the same manner (one being the broadcast-band coil described
above). However, it's impossible to place enough wire in a single layer
on the 250 - 600 kc. coil, so a different winding style is used for
this one. To wind the 250 - 600 kc. coil, drill all of the holes in
the form, but wind the secondary coil (L2) first. Solder one end of
the wire in place and make several large looping turns up to the hole
at which the secondary coil will end. Now start back down the coil and
wind in the same manner, reaching the hole in the form where the coil
started in only a few turns. Continue winding up and down the form until
the specified number of turns are in place. The purpose of this winding
method is to make as many of the turns as possible cross at angles rather
than lie parallel and thus reduce the distributed capacitance.
After the secondary has been completed, wind the primary (L1) and
tickler (L3) coils at the proper ends of the form. These coils should
be scrambled-wound, with the turns touching the ends of the secondary.
Strips of plastic cement or coil dope can be run vertically at ½"
intervals around the forms to hold the wires in place.
Various Wound Coils
Check the wiring, connect the power
supply to the receiver with the power supply cable, and plug in the
broadcast coil. Connect an antenna to the ANT 1 binding post (J1), and
a ground to the GND binding post (J3). Set the REGEN control (R2) in
the extreme counterclockwise position, the ANT (C1) and GAIN (R6) controls
in the extreme clockwise position, and the VERNIER control (C3) in the
center of its range.
Turn on the power supply. After warm-up,
turn the REGEN control clockwise until a hissing sound is heard in the
speaker. Now back off the control until the hiss just stops; this is
the most sensitive point for reception of AM stations.
have trouble separating strong local stations, turn the ANT control
counterclockwise. This increases the selectivity by decreasing the coupling
of the antenna to the receiver. With extremely strong local stations,
it may be necessary to use a very short antenna to limit the signal
When you use the short-wave coils, you'll find that
adjusting the tuning and regeneration controls is more critical. Tuning
is best done by adjusting the main dial to the vicinity of the station
you wish to hear and then doing the fine tuning with the VERNIER capacitor.
Set the regeneration control to the point where the hiss starts to receive
c.w. signals; and just below this point to receive phone signals. If
the receiver refuses to oscillate at certain dial settings, change the
antenna coupling by means of the ANT capacitor, or try the alternative
antenna connections shown in the diagram on page 40.
long-wave coil in place, the receiver should handle about as it does
on the broadcast band. And don't forget that additional coils to extend
the range in both directions can be wound in a cut-and-try fashion.
One Receiver - All Wave Parts