MACHINES & SWITCHBOARDS
Issue 2, 11/4/62
CONVERTERS, RINGING Nos. 4, 5, 6 AND 7
1. Scope of Instruction
This Instruction describes the Converters, Ringing, Nos. 4 to 7, which are
static devices for converting single-phase a.c. mains to a 25 c/s a.c. supply
for the purpose of ringing magneto bells at P.B.X.s.
Table 1 gives details of size, fixing centres and approximate weight of the
items together with the drawing and diagram references and bell ringing
The output of the Converters, Ringing, Nos. 4, 5 and 6
is a nominal 60v, and the output of the No. 7 a nominal 50v. Each converter will
ring up to four Bells No. 59A in series with a 2 uF capacitor.
Bell No. 64E, which has a loud-sounding gong, works very
efficiently with these converters. Bell No. 67A, which has a heavy movement,
also responds reasonably well if a 2 uF capacitor is connected in series.
The numbers of Bells No. 59A, each connected in series with a
2 uF capacitor, which can be rung in parallel by the output of the converters is
given in Table 1.
Consider the converter transformer as having two cores with identical secondary
windings and a common primary winding.
These cores saturate in turn on alternate positive half cycles of the half-wave
rectified mains supply. During the time a core is saturated no energy is
transferred to the output. During the time a core is not saturated (i.e. it is
working normally) a pulse of energy is transferred to the output. The
saturation pulses are at 50 c/s. The secondary windings are connected in series opposition
relative to the primary winding, therefore these output pulses will be
alternately in opposite senses, giving rise to an output at a frequency of 25
c/s. The optimum value of the capacitor which is connected to the secondary
windings of the transformer is determined by the behaviour of the converter at
low mains-input voltage and the starting of oscillations on load. Unlike a
normal LC resonant circuit, the value of this capacitor does not influence the
frequency of the output current.
When the loading on the output terminals is increased beyond
full load, the output voltage falls rapidly and the production of 25 c/s ceases. On removing the excess load, the oscillations restart. This provides a useful
The Converter, Ringing, No. 4 is for use at P.B.X.s with up to four operators'
positions, as laid down in General, S 3801.
The Converter, Ringing, No. 5 is for use at P.B.X.s
where there are 5 to 20 operators' positions or at 20-line Multiphone
switchboards. Electrically, it can be considered as the equivalent of the
Converters, Ringing, Nos. 2A and 2B. Physically, however, there is some
difference as both the No. 4 and No. 5 are for wall-mounting. By the use of two
Mountings D 91065, a Converter, Ringing, No. 4 or No. 5 may be mounted on a
standard 19in, rack, such as Racks, Apparatus, No. 42.
The Converter, Ringing, No. 6 is for use at P.B.X.s where
there are more than 21 operators' positions or at Multiphone switchboards
having 21 to 60 lines. It can be considered as an equivalent of the Converter,
Ringing, No. 3. Physically there are some differences and the Converter,
Ringing, No. 6 may be mounted on a wall or direct on a standard 19in rack. The
Converter, Ringing, No. 7 is for use at non-multiple installations.
The subscriber will provide a standard 3-pin B.S. wall-socket adjacent to the
position for mounting the converter, mains energy free of charge to the
Department and an efficient mains earth connexion. For the connexion from this
supply to the unit, Cord, Flexible, 250V, T.R.S. or P.V.C. 3-core, 0.0006 sq.
in. should be used.
|Converter, Ringing, No.
||Fixing Centres (in)
Bells No. 59A in parallel
||10 x 4.5
||10 x 8
||18 x 4
||2.25 x 3.75
Modern equivalents to the GPO Ringers