The Kasten Pz. Nr. 20 was the standard intercom box for most battle tanks of the Third Reich starting from the year 1942. This box was used in the Panzer III, Panzer IV, Panzer V, Panzer VI and Panzer VII tanks. The system in which this box was used is called the Bordsprechanlage 20.

This was a Class C audio frequency amplifier, that consisted of an RV12P2000 vacuum tube, with a potentiometer to control the grid voltage of the vacuum tube (the volume control). The Kasten Pz. Nr. 20 drew its power from one of the EU.a dynamotors through a "T" connector next to the power socket of the lower Ukw.E.e receivers.

The commander and gunner plugged in their headphones and microphones into the Kasten Pz. Nr. 21 and 22 respectively in the turrent, which were connected to the Kasten 5c which in-turn was connected to the Kasten Pz. Nr. 20 through the slip ring.

The controls for the Kasten Pz. Nr. 20 allowed for four modes of operation:

1. Radio operator is separate / RO & Commander listen to both receiver 1 and receiver 2
2. Radio operator is separate / Commander listens to receiver 1, RO listens to receiver 2
3. Radio operator connected to crew / RO & Commander listen to both receiver 1 and receiver 2
4. Radio operator connected to crew / Commander listens to receiver 1, RO listens to receiver 2

90% of the time, the Kasten Pz. Nr. 20 is set to mode #1. The theory behind this functionality, is that the crew is busy fighting the tank, while the radio operator is busy monitoring transmissions from the platoon and the command transmitter. If the radio operator wants to speak with the crew, he must turn off the receivers and transmitter, set the Kasten Pz. Nr. 20 to "Funk u. Bord" and make sure to turn the volume of the Kasten Pz. Nr. 20 down, or else he will deafen the crew, as the amplification of the RV12P2000 together with the side-tone amplifiers of the Fu5 systems packs a puch for the human ear.

If the commander wants to be connected with the radio station (radio operator + Fu5), he activates the button on his throat microphone, and is conected to the radio operator circuit of the Kasten Pz. Nr. 20. Now he's connected to the radio operator, but cannot speak with the driver and the gunner, but they can communicate with each other. At this point, the commander can hear both receivers, and may transmit from the 10W.S.c if the radio operator has switched it to "Telefonie".

Now if there is a need for the entire Panzer crew (except the loader) to talk together, the radio operator switches the top "Funk / Funk u. Bord" switch to "Funk u. Bord" which connects the Kasten Pz. Nr. 20 radio operator circuit to the main intercom circuit. This allows the crew to speak with each other. This allows the radio operator to hear important instructions from the commander, after which, he must return the "Funk / Funk u. Bord" switch back to the "Funk" position.

In mode #4, the Kasten Pz. Nr. 20 allows the entire connected crew to speak with each other, and to listen to reciever #1.

The outside of the Kasten Pz. Nr. 20. Note the red stripe under the name plate. This indicates that the box was modified in 1943 to allow the commander to patch into the radio circuit without needing the radio operator to dis-engage his microphone switch.

 

 

The cable conduit ports of the Kasten Pz. Nr. 20. In most cases only the middle port was used. A 6-wire, internally and externally shielded airplane cable was grounded to the chassis of the intercom box by being flaired out and pressed to the chassis by tightening the securing nut on the outside of the port.

 

 

The control panel of the Kasten Pz. Nr. 20. Here the radio operator connects his microphone and headphones. On/off/volume switch, intercom box controls. Even though, the Funker has a 3-pronged microphone jack, and uses a Kmf.a style microphone. the second prong and the microphone switch are disabled, therefore not effecting the relay of the Kasten Pz. Nr. 20. In the older configuration, the Funker microphone had the capability of triggering the Commander's relay, which proved redundant, as he would possibly conted with the Commander for the relay control.

 

 

Fu5/Fu2 connection panel. The left socket is for the transmiiter, and the two right sockets are for the receivers.

 

 

This is the driver's side of the Kasten Pz. Nr. 20. Here is the power socket, and the headphone and microphone sockets. Note that the driver's microphone is the Kmf.b type with two prongs, since no relay activation is necessary.

 

 

The Kasten Pz. Nr. 20 with the cover off. This is seemingly a later version of the Kasten Pz. Nr. 20 based on the smaller and cheaper transformer I filter capacitor.

 

 

Another photo of the Kasten Pz. Nr. 20 interior.

 

 

Closeup of the slip-ring connection block, and the S2 switch that controls receiver access.

 

 

The "1943 modification" red stripe on the inside of the Kasten Pz. Nr. 20.

 

 

The schematic of the Kasten Pz. Nr. 20 on the inside of the lid.

 

 

Another Kasten Pz. Nr. 20 with the "1943 modification" denoted by the red stripe.

 

 

The cable conduit ports of the Kasten Pz. Nr. 20. In most cases only the middle port was used. A 6-wire, internally and externally shielded airplane cable was grounded to the chassis of the intercom box by being flaired out and pressed to the chassis by tightening the securing nut on the outside of the port.

 

 

The control panel of the Kasten Pz. Nr. 20. Here the radio operator connects his microphone and headphones. On/off/volume switch, intercom box controls. Even though, the Funker has a 3-pronged microphone jack, and uses a Kmf.a style microphone. the second prong and the microphone switch are disabled, therefore not effecting the relay of the Kasten Pz. Nr. 20.

 

 

Fu5/Fu2 connection panel. The left socket is for the transmiiter, and the two right sockets are for the receivers.

 

 

This is the driver's side of the Kasten Pz. Nr. 20. Here is the power socket, and the headphone and microphone sockets. Note that the driver's microphone is the Kmf.b type with two prongs, since no relay activation is necessary.

 

 

Lid open. This is the rare cardboard cover for the Kasten Pz. Nr. 20 interior. Basically, don't mess with the electronics, but you can swap the tube out.

 

 

The "1943 modification" red stripe on the inside of the Kasten Pz. Nr. 20.

 

 

The earlier model larger ceramic-topped filter capacitor.