AMEGO VFO-621 Operating Instructions Manual

OPERATING INSTRUCTIONS
FOR
AMEGO VARIABLE FREQUENCY OSCILLATOR
MODEL VFO-621
DESCRIPTION
The Ameco VFO-621 is a Variable Frequency Oscil¬
lator to be used with the Ameco TX-62 Transmitter
or any other 50, 144 or 220 Me. transmitter that is
designed to operate with 8, 12 or 24-25 Me. crystals.
The Ameco VFO-621 uses the superior HETERODYNE
principle. The variable frequency oscillator operates
at a low frequency. It is then heterodyned to 24-26
Me. by means of a crystal controlled oscillator and
mixer. This permits operation of the oscillator
with one-third of the usual multiplication. The lower
multiplication, combined with the lower oscillator
frequency, permit a STABILITY and keying quality
almost non-existent on the three VHF bands.
There is no chirp with keying. The warm-up time
is very short, as both oscillators use transistors.
The internal AC power supply is Zener Diode regu¬
lated. The dial scale is calibrated for 50-52, 144-
148 and 220-225 Me. The scales are long, open and
easy to read. For mobile operation, terminals are
provided for external DC supplies (6 or 12 volts for
the filaments and 100 to 150 volts for the plates).
The cabinet height and finish match the TX-62 trans¬
mitter. It Is 6" high, 5" wide and 7-1/2" deep.
The transistors, tubes and their circuit functions
are as follows:
2SC185 transistor Variable oscillator
2SC185 transistor Crystal oscillator
6KZ8 tube (1/2) Buffer amplifier
6KZ8 tube (1/2) Mixer
6KZ8 tube Output amplifier
Silicon diode Power rectifier
Zener diode Voltage regulator
The controls are as follows:
Power switch
Band switch
Timing dial
READ THE COMPLETE SET OF INSTRUCTIONS
CAREFULLY BEFORE CONNECTING OR OPER¬
ATING THE VFO-621.
GENERAL INFORMATION
The frequency output of the VFO-621 is from 24 to
26 Me. This is divided into three bands. When con¬
nected to a transmitter, the output frequencies of
the system (VFO and transmitter) will be as follows:
Band A - 50 - 52 Me.
Band B - 144 - 147 Me.
Band C - 147 - 148 Me. and 220 - 225 Me.
Most 6 meter transmitters use crystals between
8.333 and 8.666 Me. to cover the frequency range
of 50 to 52 Me. The transmitter's first stage mul¬
tiplies the crystal frequency by 3 to obtain 25 to 26
Me. This frequency is later multiplied by 2 to get
50 to 52 Me. 8 Me. crystals are similarly used in
most 2 meter and 1-1/4 meter transmitters. The
first stage triples the frequency up to 24 Me. The
multipliers that follow bring the frequency up to
144 to 148 or 220 to 225 Me.
There are no changes needed when hooking up the
VFO-621 to a transmitter that uses 8 Me. crystals.
It is not even necessary to have a CRYSTAL-VFO
switch, nor is it important to put the switch in the
correct position when using the VFO-621 with 8 Me.
crystal transmitters that have this switch.
The above information that applies to 8 Me. crystal
transmitters also applies to transmitters using 12
to 13 Me. and 24 to 26 Me. crystals. Be sure that
one side of the crystal socket is grounded, especial¬
ly with transmitters that call for 24 to 26 Me.
crystals.
Some transmitters use 8 Me. crystals and multiply
by two instead of three in the first stage. In this
type of transmitter, it will be necessary to modify
the 16 Me. coil in the plate of the first tube to make
it tune to 24 to 26 Me. This can be done by remov¬
ing a few turns. Approximately 1/3 of the turns
must be removed. Start off by removing about 1/4
of the turns. Then check the tuning and remove
additional turns, one or two at a time, until the coil
tunes satisfactorily. The tuning can be checked best
with a grid dip oscillator. An all-band, general
coverage receiver can also be used. This will not
change the operation of the transmitter when the
same crystals are used. It merely changes the
multiplication in the first stage from 2 to 3 times.
The next stage tuning remains unchanged.
If you have any question on modifying your transmit¬
ter, send in the operating instructions and schematic
of your transmitter for further information. Include
a self-addressed, stamped envelope for return mail¬
ing of your instruction book.
INSTALLATION
1. The VFO must be connected to the common
ground on the operating table or desk. Use a #14
or heavier wire for this purpose and connect it to
any of the ground terminals at the rear of the VFO,
The grounds of all the equipment in the operating
room should be connected together and then brought
to a cold water pipe. This is an important safety
measure and should be completed before any power
switches are turned on.