Wireless of the Week - week 22

[Jesse Browning]

The sexton has a 190 control box tapped for wires that run through the vehicle conduit to the speaker at the front of the crew compartment.

[Chris Suslowicz]

Originally Posted by Jesse Browning

The sexton has a 190 control box tapped for wires that run through the vehicle conduit to the speaker at the front of the crew compartment.

Looking at the Parts Identification List (FZ256/3), the 190 is very similar to Control Unit No.3 (A or B), except that there's an extra 270 ohm resistor somewhere on the top switch, and a 3-way tag board in place of the usual 4-way one in the top box. I suspect the resistor is connected in series with the feed to the loudspeaker terminals to limit the load on the WS19 output transformers and make it look a bit more like a set of headphones. There does not appear to be a volume control anywhere in the system, nor any facility for intercom use - the loudspeaker is output only by the look of it from the component listing.

Chris.

[Jesse Browning]

Chris; does your reference give the values of the different resistors? I made a No.190 box out of a No 3 box using the wiring diagram on the lid of the main electrical junction box in the radio compartment. It doesnt give the value of the resistors. What I would prefer is an original No.190 box.

[Chris Suslowicz]

Originally Posted by Jesse Browning

Chris; does your reference give the values of the different resistors? I made a No.190 box out of a No 3 box using the wiring diagram on the lid of the main electrical junction box in the radio compartment. It doesnt give the value of the resistors. What I would prefer is an original No.190 box.

Ah, there are actually two resistors on the top switch, and 4 on the Normal/Rebroadcast switch (those are identical on 3A, 3B and 190).

The two new ones on the 190 are

17 - 1/4 W. Metallized 5,600 ohms +/- 10%
19 - 1/2 W. metallized 270 ohms +/- 10%

(Numbers are on the parts layout drawing, not component numbers.)

I wonder if there's a circuit diagram for that box in the other EMERs.

More later...

...sorry, we don't appear to have a circuit diagram of the control unit with component values. It's not in the 'First Echelon Work" EMER, which is all about operator and electrician maintenance, and the "2nd - 4th Echelon Work" just covers the set internals in extreme detail - nothing about control units.

Chris.

[Jesse Browning]

[Jesse Browning]

Super! Thanks!

[Jesse Browning]

The pictures are better than that on my phone and tablet but lose clarity when put on photobucket

[Jesse Browning]

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