February 1955 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.
Even though this CW (continuous
wave, for sending Morse code) transmitter circuit was published in 1955 in Popular
Electronics magazine, it is still legal for today's Amateur radio operator. Portions
of the 40-meter and 80-meter bands are still reserved exclusively for
CW operation. As of 2021, the 40−meter band (7.025-7.125 MHz)
and the 80−meter band (3.525-3.600 MHz) are both reserved for CW for Hams holding either
Novice (no longer issued) or Technician licenses. Additionally, the 15−meter
band (21.025-21.200 MHz) and the 2−meter band (144.0-144.1 MHz) have CW-only
areas. That is different than the frequencies
given in the article, so beware if you are tempted to throw one together for old
time's sake. The value for XTAL will need to be changed accordingly. Both bands
are a bit lower than shown here, so you might need to tweak the tuning elements
a tad as well. If you are not a designer, you would be better off just finding a
newer circuit that is already configured for the new bands.
Build This Novice CW Transmitter
By Rufus P. Turner
The beginner in ham radio with a novice license should become active as quickly
as possible with a low-powered telegraph (CW) transmitter. Operating this rig as
often as he can will give valuable on-the-air experience in handling the code and
in correct operating procedure. The best way to learn is by doing.
Note that two different coils must be built to cover both the 40 and 80 meter
A novice's first transmitter should be both simple and inexpensive. A good idea
is to use the lower frequency bands. There, the new operator usually will find more
"rag chewers" and local contacts than on the higher frequency long-distance bands.
In the 80-meter band, novice CW operation is permitted between 3700 and 3750 kc.
In the 40-meter band, the novice's territory is 7175 to 7200 kc. Crystal control
must be used.
The transmitter shown here was made especially
for beginners. While it is low-powered, it will give a good account of itself when
operated with a good antenna. It does not take up much room, since it is built on
an aluminum radio chassis box (Bender Type 145) 7" long, 5" wide, and 3" high.
To reduce expense and to keep hum-producing power equipment off the transmitter
chassis, no power supply is built into the transmitter. This allows the experimenter
to use any external unit supplying 250 volts d.c. at 50 to 65 ma. and 6.3 volts
- a.c, or d.c. at 1 ampere. Most experimenters keep a small power supply of this
type on hand for general use. Such units also can be bought cheaply in surplus.
The necessary a.c. and d.c. voltages often can be drawn from the receiver used with
the transmitter. For portable use, a 6-volt storage battery can be used in conjunction
with 180 to 225 volts of "B" batteries or a vibrator-type 250-volt supply.
schematic diagram shows the circuit of the transmitter. A 6AQ5 tube (V1)
is used in a crystal oscillator circuit. This particular circuit keys quite well.
A shunt-fed plate circuit is employed. That is, the output (tank) circuit, consisting
of coil L1 and tuning capacitor C7, is isolated from the d.c.
plate voltage of the tube by capacitor C6. This arrangement keeps d.c.
voltage off the coil and protects the operator from electric shock. Nevertheless,
switch S1 should be thrown to its "off" position before changing coils,
since the r.f. voltage may burn the fingers quite painfully just the same.
The key is plugged into jack J1 The two "Antenna" binding post terminals
are connected to the antenna.
An 8-pin octal tube socket is mounted on the left end of the chassis to hold
the crystal. Socket pins 1 and 4 receive the pins of the crystal holder, while other
pins of this socket are used as tie points for resistor R1 capacitors
C1, and C2, and leads. A 1 1/8" hole is needed for the crystal
7-pin miniature tube socket for V1, is mounted in a 5/8" -diameter hole
near the center. At the right-hand end of the chassis, a 4-pin tube socket is mounted
in a 1 1/8" hole to hold the plug-in coil.
Directly behind this coil socket is the insulated 2-terminal binding post block
for antenna connections. This block assembly is a National Type FWH. The insulating
blocks fit into 1/2" -diameter holes drilled 3/4" apart on centers.
Switch S1 jack J1 and tuning capacitor C7 are
mounted, from left to right, without insulation, along the front lip of the chassis.
The jack and tuning capacitor require 3/8" mounting holes. The toggle switch (S1)
requires a 1/2" hole. Four insulated binding posts are mounted along the rear lip
of the chassis for connections to 6.3 volts and 250 volts.
The two coils are wound on conventional 1" -diameter, 4-pin, phenolic plug-in
forms. The accompanying coil table gives instructions for winding these coils. Each
consists of a main coil L1 and a coupling coil L2 The ends
of L1 are fed into the two large pins of the form and soldered. The ends
of L2 are fed into the two small pins and soldered.
For adjusting the transmitter, make a test lamp by forming a 1 1/4" -diameter
loop of insulated hookup wire and soldering its two ends to the terminals of a 6-volt
Obtain an 80-meter crystal on any frequency between 3700 and 3750 kc, and a 40-meter
crystal on any frequency between 7175 and 7200 kc. Several crystals in each frequency
range will allow movement "around the band" when interference sets in.
simplest antenna to use with this transmitter is the center-fed type (cut for 40
or 80 meters) with coaxial or low-impedance ribbon feeder. Antenna dimensions and
building instructions may be found in any amateur handbook. Other types of antennas
may require a coupling coil and tuning capacitor external to the transmitter.
To place the transmitter into operation: (a) Plug in an 80-meter crystal. (b)
Plug in the 80-meter coil. (c) Connect the 6.3 v. and 250 v. power supply. (d)·Throw
the switch S1 to "on." (e) When the tube has heated, plug the key into
jack J1. (f) Hold the loop of the test lamp over the top of the coil.
(g) Depress the key; while holding it, adjust tuning capacitor C7 until
the lamp lights. Back away with the lamp if it is burning too brightly. (h) Tune
capacitor C7 for brightest lamp response. (i) Taking care that the key
is in its up or "off" position, connect the antenna leads to the "Antenna" binding
posts. (j) Again, close the key, hold the lamp loop near the coil, and retune capacitor
C7 for brightest lamp response.
When wiring the transmitter follow both schematic and pictorial diagrams closely.
The transmitter now is tuned-up on 80 meters, and is ready to go. The signal
may be monitored for smoothness by listening to it with a receiver (minus antenna)
or on a c w monitor.
To tune up on 40 meters, repeat the entire process with a 40-meter crystal and
the 40-meter coil plugged in.
If you do not have any of the power sources mentioned in the early part of this
article, you can use this transmitter with a power supply to be described in the
next issue of POPULAR ELECTRONICS
Posted October 21, 2021
(updated from original post on 8/21/2011)