Wireless of the Week - week 22

[Jesse Browning]

Above the top switch, under the heading "LOUDSPEAKER" are "A","OFF", B. So clearly the loudspeaker was used for the 19 set.

[Chris Suslowicz]

Originally Posted by Jesse Browning

Above the top switch, under the heading "LOUDSPEAKER" are "A","OFF", B. So clearly the loudspeaker was used for the 19 set.

Yes, I'm trying to work out the switching arrangements. (In order to determine which resistor goes where, and what their purpose is.) There appears to be a feed from the 'Speech' line as well, presumably to add the intercom audio to the loudspeaker output.

Has anyone got the circuit diagram of the loudspeaker? (I assume the terminals connect to different tappings on the matching transformer, or the WS19 terminals bypass the push button/capacitor arrangement used with the telephone system.)

More in a while....

Chris.

[Jesse Browning]

I could email you a better picture of the wiring diagram. The speaker I have only has two terminals. The only WWII picture I have of a speaker in a sexton shows only two terminals. I wonder if that would exclude its use with the radio?

[Chris Suslowicz]

Originally Posted by Jesse Browning

I could email you a better picture of the wiring diagram. The speaker I have only has two terminals. The only WWII picture I have of a speaker in a sexton shows only two terminals. I wonder if that would exclude its use with the radio?

No, if the Sexton has only two terminals, then it's only for use with the WS19 (I think).

Control Unit 190 is a bit complicated (well, they all got bit complicated when the rebroadcast facility was added), but I'm getting there.

The top (3 terminal) tagstrip is for Driver Intercom, and has Speech, Mic+ and Ground.

The next tagstrip (2 terminal) is for the loudspeaker connection.

The switch has 3 wafers with 3 sets of contacts on each; from left to right (as shown on the wiring plate):

1) Loudspeaker Return - connected to ground in all positions.

2) Loudspeaker Feed - selects source via 5, 7 & 8

3) not used

4) Feeds set audio into the intercom amplifier via a resistor (this is probably the 5,600 ohm resistor, because the contacts are connected to the A and B set Tel+ output (i.e. phones) and the wiper goes via the resistor to the intercom Mic+ connection).

5) 'A' set feed if rebroadcast selection set to A&B when on IC (I think).

6) not used

7) 'B' set set feed if rebroadcast selection set to A&B when on IC (I think).

8) Set selection to Speech (intercom output) line. Centre position shorts out a resistor - this will be the low value (270 ohm) one, I think, to compensate for the loudspeaker being disconnected.

9) 'A' set unattended line - connects this to ground if the loudspeaker is switched to 'B', so that the red lamp will light if the operator's droplead is also switched to 'B', indicating that nobody is monitoring the 'A' set output.

I think that's how it all works!

Chris.

[Jesse Browning]

Sounds right. I installed the radio last year, but can only listen to it through the tannoy. Im in the process or rebuilding the 4 headsets used in the vehicle so the intercom can be utilized.

[David Dunlop]

Chris.

In Bruce's first post on this thread, last photo, the image is the information plate inside the cover. The section dealing with the loudspeaker states the two terminals marked '19-Set' are connected to windings of 30 ohm value to match the output from the I/C amp in the 19-Set, if that helps at all.

David

[Chris Suslowicz]

Originally Posted by David Dunlop

Chris.

In Bruce's first post on this thread, last photo, the image is the information plate inside the cover. The section dealing with the loudspeaker states the two terminals marked '19-Set' are connected to windings of 30 ohm value to match the output from the I/C amp in the 19-Set, if that helps at all.

David

It does.

The loudspeaker is obviously a rather heavier load than a couple of headsets, so needs to connect to the IC amplifier rather than one of the set outputs.

The Control Unit 190 is an odd beast with a single droplead for the wireless operator, so everybody else must be using the intercom - either via Junction Distribution boxes (No.3 or No.4 because the Mic+ line feeds into the IC amplifier so it can't be for the power microphone) or the loudspeaker (presumably once the gun is deployed).

Chris.