Remember when reading this document that it uses 'D.C.'
as an abbreviation for 'Dramatic Control' and not for 'Direct Current'! The
plugging operations described took place in the main Control Rooms, not in
the studios, and all the amplifiers were also in the Control Rooms.
SIX-CHANNEL DRAMATIC CONTROL UNIT DC/4
Programme Connections
The DC/4 unit has six programme input channels and incorporates cue
light keys, D.C. return lights, channel engaged lamps, loudspeaker volume
control and housephone jacks. (The DC/4 installed in Birmingham is not quite
standard, the D.C. return lights being operated from the mains instead of
from the 24 volt battery. The DC/2 unit differs from the standard DC/4 unit
in respect of the omission of the D.C. return light circuits, while the cue
light keys and loudspeaker control are mounted on a separate panel.)
Referring to Figure 1, the six programme channel inputs terminate on
the Echo & D.C. jackfield where each is equipped with an input and
listen jack.
The No.1 outputs of the studio and echo 'A' amplifiers and of the 'D' amplifiers
(the latter via tie-lines connecting with the Line Termination bay jackfield)
are available on the Echo & D.C. jackfield for connection to the channel input
jacks by means of double-ended cords as required.
Associated with each of the channels there is a fade control on the D.C. unit,
and above each there is a channel engaged lamp provided with a socket
into which can be fitted a lamp cap indicator marked to designate the programme
source connected to the particular channel. The act of plugging up causes
this channel engaged lamp to light via the sleeve circuit.
The E relay also operates, in series with the Channel engaged lamp,
and connects -24 volt to the private wire of the 'A' or 'D' amplifier associated
with the source causing the amplifier L.T. relay to operate, and to
the circuit engaged lamp over the corresponding punching key on the S.B. &
Operating position causing the lamp to light.
However, the amplifier should always be switched on manually so as to ensure
that it will not be affected if the channel engaged lamp should fail.
The programme wiring is shown in Figure 2. The channels are arranged on the
dramatic control panel in two groups of three, with a central mixer
for selecting either the group comprising channels 1, 2 and 3 or that comprising
channels 4, 5 and 6. The channel inputs are connected via transformers to
the channel fade potentiometers. The outputs of the three potentiometers
in each group are connected in series across the appropriate input channel
of the central mixer. This is a two-channel fade unit of the usual balanced
type providing a gradual fade from one group to the other, the unwanted group
only being completely faded out on the last stud. The output of the central
mixer is transformer coupled to the output terminals which are permanently
wired to the input of the DCA amplifier. The output of this amplifier
is connected to the 'B' input switching relays.
The talking-back microphone is permanently wired to terminals 73 and 74 and
terminals 77 and 78 are connected to the input of the spare 'A' amplifier,
the output of which is connected to the make contacts of the CO relay
(Figure 3).
At certain stations the input and output of the spare 'A' amplifier are permanently
wired via break jacks to the D.C. talking-back circuit, while at others the
microphone output and the contacts of the CO relay are wired to jacks on the
'A' amplifier bay and the input and output of the spare 'A' amplifier must
be plugged up to them.
The amplifier can be switched on by means of the key on the amplifier bay,
but at some stations a switch for the purpose is fitted on the D.C. unit.
Figure 2 also shows the D.C. housephone circuit jacks the outers of which
are wired to the outers of the LS & HP Input jack in the Loudspeaker
jackfield (Figure 3).
Loudspeaker Switching
The loudspeaker connections are performed by means of plugging operations
on the Housephone & Loudspeaker jackfield and can be followed by reference
to Figure 3 (above, or click on the image for a larger version in a
new browser tab).
The Studio LS jacks of the individual studios must be plugged up to
the DC. LS Chan jacks to correspond with the plugging up of the studio
outputs to the D.C. input channels on the Echo and D.C. jackfield. The LS
& HP Input jack and the DC. LS Input jack must be plugged up to
the TV. LS Output jack of the trap valve amplifier connected in the
output of the 'B' amplifier to which the D.C. output is connected. The CH.
In jack must be connected, in the case of a transmission, to the Trans
jack and, in the case of a rehearsal, to the Reh jack. Where echo is
being used on one of the programme sources, connection must also be made between
the DC. LS Echo Chan jack of the channel to which the programme source
is connected and the DC. LS Chan jack of the channel to which the echo
'A' amplifier output is connected.
The outers of the DC. LS Chan jacks, to which the Studio LS
jacks are plugged up, are connected each to the travellers of an LS. CO
relay associated with the particular channel. The make contacts of this relay
are connected, via the inners of the associated DC. LS Echo Chan jack,
to the outers of the CH. In jack , which is connected via the Trans
or Reh jack, as the case may be, and the LS & HP Input jack
to the trap valve loudspeaker output. Thus, when the particular LS. CO
relay operates the studio loudspeaker is connected to the output of the trap
valve amplifier.
One side of the winding of all the LS. CO relays is connected to -24
volts. The other side of the winding is connected to a switch on the associated
channel fade control and also to one of the back contacts of the P relay
associated with the group to which the channel belongs. When the particular
channel is faded out (through 0 to LS) the switch closes and applies +24 volts
to the winding of the associated LS. CO relay, which operates giving
the particular studio its loudspeaker. When the central mixer is turned
to either of its extreme positions, +24 volts is applied via an auxiliary
slider to the winding of the P relay associated with the group of channels
faded out. The relay operates closing its three contacts and causing the LS.
CO relays connected to them to operate, thereby connecting the loudspeaker
in the associated studios. These arrangements ensure that the loudspeaker
will not be in operation in any studio while the channel to which its microphone
is connected, is faded up.
But for the DC. LS Echo Chan jack connection, it would be possible,
when echo is being used on any studio, for the producer to cause the whole
system to howl if he omitted to fade out the echo channel at the same time
as he faded out the direct programme source; for, as soon as the studio channel
was faded out the loudspeaker in that studio would be brought into circuit,
while, seeing that the echo channel was not faded out, the microphone in the
same studio would be connected, via the No.2 output of its 'A' amplifier and
the echo room, to the loudspeaker input. To obviate this condition connection
is made, as previously stated, between the DC. LS Echo Chan jack of
the channel to which the studio is connected and the DC. LS Chan jack
of the channel to which the echo output is connected.
For example, suppose the studio output is connected to channel 5 and
the echo on this studio to channel 6, then the studio loudspeaker input
is connected to the DC. LS Chan 5 jack and the DC. LS Chan 6
jack is connected to the DC. LS Echo Chan 5 jack. The inners of this
last jack are disconnected by the act of plugging in. Consequently the studio
loudspeaker input will only be connected across the CR. In jack, (via
the inners of the DC. LS Echo Chan 6 jack ) when both the LS CO.
5 and LS. CO 6 relays have operated. This means that the studio
only gets its loudspeaker when both the direct and echo channels have
been faded out or, of course, if the group comprising channels 4, 5 and 6
has been faded out on the central mixer.
Talking-Back Circuits
The rehearsal talking-back arrangements differ from those for transmission.
In the former case the production can be held up for the purpose and the studio
loudspeakers can therefore be used. But in the case of a transmission the
operation of the talking-back circuit obviously must not be allowed to interrupt
the performance, and so the housephone circuits are used.
The input circuit of the loudspeaker in the D.C. room is connected
to the travellers of the LSS relay. When the talking-back key on the
panel is in the central (or LS) position, the back contacts of this
relay are made and the LSM connected across the output of the loudspeaker
control potentiometer on the panel. Operation of the talking-back key to either
its LS Off or Speak position applies +24 volts to the winding
of the LSS relay, which operates and disconnects the D.C. loudspeaker.
For a transmission, connection is made, as previously stated, between
the CH In and Trans jacks. Where necessary, the spare 'A' amplifier
must be plugged up, by means of jacks provided on the 'A' amplifier bay jackfield,
to the talking-back circuit, the amplifier input being connected to the output
of the talking-back microphone and the amplifier output to the talking-back
relay switching circuit. The housephone inputs of the studios to be used must
be plugged up to the strip of parallel jacks in the Loudspeaker & Housephone
jackfield, wired to the D.C. housephone switching circuit.
The Trans jack is connected, in parallel with the LS & HP Input
jack, to which the TV. LS output is plugged up, to the back contacts
of the CO relay. The studio housephone input circuit is connected to
the travellers of this relay. The output of the spare 'A' amplifier, used
with the talking-back microphone is connected to its front contacts. When
the talkingback key is held in the Speak position, relay S operates,
completing a circuit for the operation of the CO relay, which transfers
the housephone circuit connection from the trap valve output to the talking-back
amplifier output.
For a rehearsal, the CH In and Reh jacks are plugged
up to one another and, where necessary, the input and output connections of
the spare 'A' amplifier completed as before.
When the talking-back key is held in the Speak position the M
relay operates over the sleeve circuit. This relay completes the operating
circuit of both P relays, thereby causing all of the LS. CO
relays to operate and all the studio loudspeakers to be connected in parallel,
via the CH In and Reh jacks, across the travellers of the CO
relay. As before, the operation of the S relay completes a circuit
for the operation of the CO relay and transfers the loudspeaker and
housephone connection from the TV. LS output to the output of the talkingback
'A' amplifier.
Release of the talking-back key restores the original condition of the circuits,
but if the CO and LSS relays were allowed to release first there
would be a momentary howl. A 25µF. condenser, sometimes in series with
a 600Ω resistance, is, therefore, shunted across the windings of the CO
and LSS relays in order to delay their release sufficiently to allow
the P and LS. CO relays to restore first.
Cue Light and Return Circuits
The cue and return light circuits are shown only in the case of the loudspeaker
circuits connected to channels 1 and 2, although similar equipment is provided
for all the studio loudspeaker circuits.
The operation of the cue light key associated with a particular channel
connects -24 volts, which is standing on the make contact of the key, via
the sleeve circuit of the associated DC. LS Chan and Studio LS
jacks, and the normally-made back contact of the DCR relay, to one
side of the winding of the LC relay, on the other side of which +24
volts is standing. The LC relay, therefore , operates, closing the
mains circuit which lights the cue light in the studio.
The studio can signal back to the D.C. position by means of the return
light circuit. Operation of the studio push provides a circuit for the
operation of the DCR relay. This connects -24 volts via the sleeve
circuit of the Studio LS and DC. LS Chan jacks and the contacts
of the key (in the unoperated position) to one side of the associated D.C.
return lamp, which lights.
Summary of Connections for D.C. Working
Programme Connections (Echo & D.C. Jackfield)
For direct programme sources, double-end between D.C. Chan inputs
and the 'A' or 'D' amplifier No.1 outputs, in accordance with the grouping
requirements for the particular production.
For echo sources, double-end between the 'A' or 'D' amplifier No.2
outputs and separate echo inputs, and double-end between the associated
echo 'A' outputs and D.C. Chan inputs, according to the grouping
requirements for the particular production.
On the panel insert lamp caps for the channel engaged lamps designated to
correspond with the programme connections set up.
Loudspeaker and Housephone Connections (Loudspeaker & Housephone
Jackfield)
Double-end between the Studio LS Input and DC. LS Chan jacks
to correspond with the direct programme input connections. Where echo is used,
double-end between the DC. LS Chan jack of the channel to which the
echo source is connected and the DC. LS Echo Chan jack of the
channel to which the direct programme source is connected.
Double-end from the Trap Valve LS Output to the DC. LS Input and LS
& HP Input jacks.
For a transmission, double-end between CH. In and Trans and
between the Studio HP inputs and the D.C. HP parallel jacks.
For a rehearsal, double-end between CH. In and Reh.
Talking-back Microphone ('A' Amplifier Bay)
At stations where the spare 'A' amplifier is not permanently wired to the
D.C. talking back circuit, double-end between the talking-back microphone
output and the spare 'A' amplifier apparatus input, and between the D.C. talking-back
circuit input and the spare 'A' amplifier apparatus output.
Control and Signalling Connections
Switch on the 'A' or 'D,' 'A,' Echo 'A,' trap valve, and DCA amplifiers by
means of the manually operated keys on the amplifier bays. For a transmission,
punch up the 'C' amplifiers of the lines to which the programme is to be sent
to the output of the 'B' amplifier, and punch up its input to the DC
output. For signalling the studios, operate the DC Con key and then
the signalling keys of the various studios required. Finally operate the DC
key when the programme is faded up.