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Radio
HSA
Thales
  
RT-3600 →
RT-4600 →
  
KL/GRA-3686
Radio Remote Control Set

KL/GRA-3686 is a remote control set for a number of military HF/VHF radio sets of Philips, HSA, Thomson and Thales, developed around 1987 by Hollandse Signaalapparaten (HSA) 2 in Huizen (Netherlands). The set consists of two units — a local device and a remote one — and was initially developed for the RT-3600 and RT-4600 radios – in which case it replaced the earlier KL/GRA-6 remote control set – although additional versions were available for other radios, such as SPIDER.

The set consists of two similar boxes that allow two radios to be controlled via a regular 2-wire line (WD-1/TT) that can be extended up to 3 km. One box – the Local Control Box (LCB) – is fitted close to the radio, whilst the Remote Control Box (RCB) is placed at the other end of the field line.

The image on the right shows the two boxes. At the left is the LCB which has two fixed cables for connection to one or two radios. At the right is the RCB, with an H-5050 handset connected. A second H-5050 handset can be connected to the LCB for direct communication with the RCB.
  
KL-GRA-3686

The devices are powered by three common D-size dry battery cells of 1.5V each, that are held in a cylindrical battery compartment that can be accessed via a large circular screw-cap at the side. Up to two radio sets can be controlled in simplex or duplex mode, from the Remote Control Box (RCB) as well as from the Local Control Box (LCB). The standard version of the KL/GRA-3686, also known as the A-version, was intended for use with the Philips RT-3600 and RT-4600 radios.

Green rubberised carrying bag
KL-GRA3686 complete set
KL-GRA-3686
Local Control Box with fixed cables
Remote Control Box (RCB) C-3686
 Instruction card IK-11-473
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Green rubberised carrying bag
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KL-GRA3686 complete set
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KL-GRA-3686
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Local Control Box with fixed cables
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Remote Control Box (RCB) C-3686
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 Instruction card IK-11-473

Setup
The diagram below shows a typical setup of the KL/GRA-3686. At the left is the C-3686A Local Control Box (LCB), which can be connected to one or two 3600/4600 radios. In case of stand-alone use, a handset can be connected directly to this unit. In all other cases, a standard 2-wire field telephone line (WD-1/TT) is connected to the two terminals at the right of the front panel.


At the other end, the 2-wire line is connected to the terminals at the left of the front panel of the C-3686 Remote Control Box (RCB). A standard H-6060 handset 1 can be connected to either of the two control boxes, and a MODE selector allows any combination of the two connected radios for RX and TX, allowing single-channel (simplex) or split-frequency (half-duplex) operation [A]. A direct call between the LCB and RCB is possible, by placing the MODE selector in the TEL position and pressing the red CALL-button at the top right. This will ring the buzzer at the other end.


The LCB can also be used on its own, as a local radio remote control unit, for example when used inside a vehicle. In that case, the distance between the LCB and the radio is limited by the length of the 10-way cable. In addition, it allows half-duplex operation by adding an second radio.


Features
The diagram below shows the front panel of the Remote Control Box (RCB). At the left are the terminals for the 2-wire field telephone line. To the right of the lower terminal is the MODE-selector, which also acts as the power switch. Directly above it, are the buzzer and the ringer volume knob, which are used in case of a direct call from the Local Control Box (LCB).

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At the right are the sockets for connection of the H-5050 handset and the optional LS-166/U speaker. There are three red LED indicators on the front panel: for battery level, radio 1 transmission and radio 2 transmission, each of which can be covered by a pivoting flap. At the right side is a large screw-cap behind which the three 1.5V D-size batteries are installed.

MODE selector
  • OFF
    Power off
  • BATT
    Check battery voltage level (uses the optical indicator)
  • TEL
    Direct call to the RCB (telephone)
  • TX1/RX1
    Simplex on radio 1
  • TX1/RX1+RX2
    Transmit on radio 1, receive both radios
  • TX2/RX1+RX2
    Transmit on radio 2, receive both radios
  • TX2/RX2
    Simplex on radio 2
Versions
The C-3686 Remote Control Box (RCB) is a universal part and is the same for all versions of the KL/GRA-3686. The C-3686-x Local Control Box (LCB) however, can be adapted for a specific radio set, identified by a single-letter suffix. The following versions are currently known:

  1. In the case of the SPIDER-variant – the KL-GRA-63686(S) – a handset with an old-type 10-pin plug was used, as the 5-pin U-229 sockets on the front panels were replaced by a 10-pin U-79/U sockets.
  2. The suffix 'S' is uncertain, as the name tag of the Spider-version of the KL/GRA-3686 in our collection appears to be missing.



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Parts
Green rubberised carrying bag
Bag
Remote Control Box C-3686
RCB
Local Control Box C-3686A
LCB
H-6060 handset (2)
Loudspeaker set LS-166/U
Instruction Card IK-11-473
Carrying bag   CY-3686
The complete set was supplied in the green rubberised carrying bag shown in the image on the right. It has two compartments: one for the Remote Control Box (RCB), and a larger one for the Local Control Box (LCB) and its cables.

In some cases, the optional LS-166/U speaker was also stowed in the larger compartment. The two HC-5050 handsets are stowed at the top.
  
Green rubberised carrying bag

Remote Control Box (RCB)   C-3686
The Remote Control Box (RCB) is used at the far end of a 2-wire field telphone line that can be up to 3 km long. It has sockets for a HC-5050 handset and for a speaker, and is powered by three internal 1.5V D-size batteries.

The device can control up to two radio sets, in simplex and duplex mode. It can also be used for direct communication with the Local Control Box (LCB) without accessing the radio.
  
Remote Control Box (RCB) C-3686

Local Control Box (LCB)   C-3686A
The Local Control Box (LCB) is the interface from one or two radio sets, to a 2-wire field telephone line that can be up to 3 km long. It can also be used for direct communication with the Remote Control Box (RCB). At the left are two fixed cables 1 that should be connected to the audio in/out sockets of the radio(s).

Depending on the version, different connectors may be present at the far end of these cables. The standard version of the LCB (C-3686-A) is wired for the RT-3600 and RT-4600 radios. The device shown here is a C-3686-B, which is wired for a different radio.
  
Local Control Box (LCB) C-3686-B

  1. Note that the SPIDER-version of the LCB has sockets instead of fixed cables.

Handset   H-6060
Each KL-GRA-3686 set came with two identical HC-5050 handsets, one of which should be connected to the LCB, and one to the RCB.

Note that these handsets have a dynamic microphone element, and are exclusively supplied for this set. They can not be replaced by handsets with a carbon type microphone.
  
H-5050 handset

Speaker   LS-166/U
A standard LS-166/U speaker can be connected to the 10-pin U-79/U socket at the front panel of the Remote Control Box (RCB). This was the standard speaker for European and American military radio sets in the 1970s and 80s.

The LS-166/U speaker is currently missing from our collection.
  
LS-166/U speaker

Instruction Card   IK-11-473
The set came with a yellow folded instruction card IK-11-473, in the Dutch language. It explains how to connect the two units and how to operate them in the field.

The card was made specificially for use with the C-3686-A in combination with the RT-3600 or RT-4600 radio, but is also applicable to other versions of the KL-GRA-3686.

 Download instruction card
  
 Instruction card IK-11-473

Green rubberised carrying bag
KL/GRA3686 inside green carrying bag
H-5050 handset
Remote Control Box (RCB) C-3686
Front panel of RCB (C-3686)
Local Control Box (LCB) C-3686-B
Local Control Box with fixed cables
 Instruction card IK-11-473
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Green rubberised carrying bag
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KL/GRA3686 inside green carrying bag
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H-5050 handset
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Remote Control Box (RCB) C-3686
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Front panel of RCB (C-3686)
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Local Control Box (LCB) C-3686-B
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Local Control Box with fixed cables
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 Instruction card IK-11-473

Interior
The interior of the device(s) can be accessed by loosening the four large bolts in the corners of the front panels, and sliding off the rear case shells. Note that the case shell holds the battery compartment which is fitted to the main unit by means of a fixed 2-wire (red/black) connection.

The image on the right shows the interior of the C-3686A Local Control Box (LCB). The electronic circuits are divided over two PCBs that are both fitted to the rear of the front panel. These PCBs hold the electronics for the audio amplifiers and the digitally encoded signal for the 2-wire line.

Three small PCBs with filtering components are fitted close to each of the sockets. Furthermore, a special filtering PCB is mounted directly to the terminals of the 2-wire interface. It also holds a line transformer, which is similar to the trans­former of a common (analogue) telephone set.
  
Interior

The device is powered by three D-size dry battery cells that should be installed in the cylindrical battery holder that is mounted at the centre of the case shell. It is clearly visible in the image above. To save batteries, the MODE selector should be set to OFF when the device is not used.

Interior
Interior
Quick glance at one of the PCBs
Quick glance at the other PCB
Top view
Modifications
Wiring to the radio sockets
2-wire interface transformer
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Interior
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Interior
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Quick glance at one of the PCBs
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Quick glance at the other PCB
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Top view
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Modifications
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Wiring to the radio sockets
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2-wire interface transformer

Documentation
  1. Instructiekaart IK 11-473, Afstandsbedieningsuitrusting KL/GRA-3686
    Instruction card IK 11-473, remote control set KL-/GRA-3686 (Dutch).
    Royal Dutch Army, 8 January 1987. #CM303000
Further information
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Crypto Museum. Created: Saturday 21 November 2020. Last changed: Sunday, 29 November 2020 - 18:42 CET.
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