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
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.
January 1963 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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One Receiver, All Bands
thanks to plug-in coils...
By Philip E. Hatfield,
Receiving Tube Dept., General Electric Co., Owensboro,
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 power amplifier.
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."
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.
For maximum 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.
The Receiver. 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."
is the word on antenna hookups for this receiver, and three
possible configurations are shown.
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.
the 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.
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.
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 Coils. Before the 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
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 tension.
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.
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
Operation. 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.
If you 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 strength.
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.
With the 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