Bendix aircraft transmitter TA 12.

The Bendix transmitter TA 12.

TA 12 front 2

This transmitter is originally an American made aircraft transmitter, but also used in the British Royal Airforce (RAF). Aircrafts like Mosquitos.

The  TA 12 has four frequency bands, one for longwave and 3 for shortwave. The funny thing is that each frequency band,  has it’s own VFO,  and only one poweramplifier for all of them, but again 4 output tuning filters with variometer inductance, to match it to the antenna. It delivers about 40 – 50 Watts on phone and CW. Modulation art, A-G2 modulation. In the mid the earial current meter.

The four knobs at the left are the channel preselector tunings, for each wave band one. Left of the knobs are the channel numbers you preselected. In the mid under you can see the knob for preselecting one of the four wave bands.

At the right are the four knobs for tuning, by variometer inductance,  the output filters for matching the transmitter to the antenna.

In the beginning, by lack of the original powersupply/modulator unit, type MT 28 BA , I used a separate modulator, homemade, with 2 valves 807 in the final.  With Ronette crystal microphone. It was doing very well. Also a homemade mains powersupply is used.

But some time ago, I managed to buy one on EBAY, a MT28BA. See the pictures below.

Bendix_MP-28BA (1)

Sideview with power connector.


Inside view with at the left the Audio PA amplifier valves, in the mid, the modulation transformer.


View components, at the right, the several fuses and the switch for switching from carbon mic to dynamic mic.

The unit had to be cleaned a bit and inspected.  But  nothing was wrong with it. The unit came also with home made cables and control box for working with the transmitter on AM, CW and MCW. For AM I used a T17 carbon microphone. Modulation deph 100 %. The noise level of the rotary transformer is not to heavy. It starts only at CW (contineously) and at AM (during transmitting).

Behind a small panel, you can chose by a switch, between a carbon mic or a dynamic mic. Note that at a type MT 28 B, this provision is not available.

Inside the transmitter.

TA 12 upper

The upper view of the transmitter.

The box at the right is the VFO compartment. At the left upper, one of the four variometer inductances, four each band one.

TA12 relay

View at the HF power amplifier with relay for switching the antenna and HT to the amplifier. The 2 tubes are in parallel.

TA 12 under

The under view of the transmitter. The motor for automatic channel switching at the left is missing. At the right, the VFO box again.

TA12 side

Side view with the four tubes of the seperate VFO parts. Each frequency band  has it’s own VFO part, so also it’s own tube. Left up the power input connector.

The modulator unit is doing very well. In mode AM, I can make almost 100 % modulation depth.  On CW, the tone is very stable. A pleasant way of working with it.

Aerial Artificial type 1A

Aerial Artificial type 1A

The Aerial Artificial type 1A is used in the RAF for aligning the output transmitter stage of the pre-war T 1083 for test purposes. This type 1A is a prewar type.

A schematic diagram is shown is picture 1. Note the different conections for the different frequence ranges.

It can also be used very easily for aligning the TR 1196 or TR 9.

Aerial Artificial  1A

The front and the electrical diagram.


The front of my set.


Here you can see the Artificial Aerial, used by the Australian Army in testing the transmitters,

type T-1083.

The Artificial Aerial to be seen on the left on the shelve.


Transmitter/receiver TR 9-F


A short historie of the TR 9 and his successors.

The TR 9 is the pre war wellknown sender receiver.  Although the type 9 F is was used in the bigger aircrafts like the early Lancaster bomber etc. for communication between the airfieldtower and the aircraft or in close distance to others. The TR9 D is slightly different. It was fully remote controlled bij bowden cables. The TR 9 (D) were used in the Spitfire and Hurricane.

The TR9 F and D were especially used in the beginning of the war, in the battle of Brittain. Although his succesor, the TR 1133 was already there. The TR9 was in use in the Battle of Brittain instead, but not his succesor TR 1133, which supposed to be. The production of the TR 1133 was to small to deliver enough sets for the RAF at that time. They needed more transceivers for their increasing amount of fighters.

The TR 1133 was a VHF set with a frequency cover of 110 – 120 MHZ, and an output of about 5 watts, instead of that the TR 9 providing only 0,5 watts. The increasement of output was a big advantage.

The TR 1133 was already in use in the Spitfire and Hurricane at the withdrawal of the British army at Dunkirk in the beginning of the war. During the withdrawal the sets were all disadmantled out of the left behind airplanes, to avoid that they became in enemy hands.

But the TR9 stayed in service till after the battle of Brittain. Before the TR9 was superseeded after the battle by the TR 1133, the TR 1196 was introduced. The TR 1196 has a frequency range of 4,3 – 6,9 MHZ. The advantage of the receiver of the TR 1196, was that the receiver was crystalcontrolled.

After the TR 1196, came finally at the end of the war the TR 1133, a VHF set. But the TR 1133 was not so succesful and was soon replaced by the TR 1143.

Because there was a big cooperation between Brittain and the USA, they gave the design of it to the Americans. The designed the SCR 522 , with receiver the BC 24, and transmitter BC 625. It was almost the same design like the TR 1143. It was almost equal, even the typical british jones plug were used.

The SCR 522 was also used by the RAF in their fighterplanes.

Some technical details:

In the first early Lancasters, the TR9 F was positioned under the navigator table. And was used by the pilot for communication between airfield tower or between the squadron airplanes.

In the TR9D, the receiver type R1120 and the transmitter type T1119 is used, while in the TR9F the receiver type R 1139 and transmitter type T 1138. The receivers have the same schematic, but the transmitter has a different schematic. It is the internal connection I/C which is in the T 1138 is not connected, while in the T 1119 is. The I/C connector is an extra connection to input of the 3-stage audio amplifier in the receiver. In the T 1119 transmitter the I/C is connected to the external mic . So in the TR 9 D the 3-stage audioamplifier can be used also as an intercommunication amplifier.

In the T 1138 transmitter the external mic is connected to the micc transformer V3. This external mic connection can be connected externally to an A 1134 intercom amplifier acting as a preamplifier for an dynamic microphone. This for modulating the transmitter in mode A3 (anode/screen modulation).

My TR8 F It is working now in the 40 meter band with a crystal on 7078 Khz. It gives 2 mA on his antenna current meter into a Aerial Artificial no 1 A. ( See also the post Aerial Artificial no 1A). That supposed to be about 0,5 watts.

The receiver is a TRF receiver. It consists of two HF amplifiers, VRSG 18. Backfeed could be arranged in the second HF amplifier. This is arranged by a variabel condensor, which can be tuned on the front of theTR9. Called reaction.

A VR 21 is used as a triode detector. Followed by a three stage audioamplifier with also VR 21 triodes.

The transmitter is a three stage type and crystal controled.

One VT 20 as a crystal oscillator , A second one, VRSG 18 as a power amplifier. Also a a VRSG 18 as a modulation amplifier for A3 mode.

The transmitter has 2 channels. One is the normal channel N for communication and the S channel is the special frequency channel, which could be used for  PIPSQUEAK purposes. This system is discribed in the post PIPSQUEAK.

The front of the transmitter. 

Kerst 2008 065

Inside the transmitter.

Kerst 2008 064

The power amplifier tube in  the transmitter.

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The power amplifier anode coil in  the transmitter.

The front of the TR9 F. Left the transmitterpart, right the receiverpart.

The intercom amplifier, type A 1368 connected, by lack of the original used amplifier type A 1134, to a homemade plugboard. My A 1134 is used for the T 1154 transmitter.

The front of the A 1368. Note the missing switch at the left , which is there at the A 1134. The amplifiers are the same, with same radio valves, same powersupply voltages 2 volt DC and 120 volt DC. Only the connector on the plugboard are smaller ones. So my plugboard can not be used with the A 1134.

Board with headphones connection, psu connection and the volume gain knob. The volume regulates the Second grid of the HF amplifier of the receiver.

This is a picture of a TR 9 in the Science museum. Probably the TR 9 D for fighterplanes, Spitfire, Hurricane. Watch the remotecontrole with bowden cables and in the mid the volume gain control. The remote control is extremely rare and hard to get.

The above pictures the setup of the TR9D in larger airplanes, like the Lancaster bombrer.

TR 1196



four channels.

 Working condition.

This is a  transmitter-receiver used in multi seater airplanes like the early Lancaster etc. replacing the TR9 F in that place.

It was used for a short distance communication. The set was placed in a spitfire fighter just behind the pilot, just like the former TR9. In the Lancaster in the mid of the fuseleg.

It is a four channel transmitter. For the receiver, as well as the transmitter, four crystals are used.

The diffents units were: receiver type 25, transmitter type 22 and the rotary transformer powersupply type 104.

To handle the transceiver was much easier then the TR9, because of the 4 channels  in receiver and also transmitter.

Channel 1 was used for close distance to the airfield, channel 2 for  communication far away from the airfield at close distance, channel 3 was the Command Quard frequency and channel 4 for “Darky Frequency”. Just like in the TR9, the “Darky Frequency”was a frequency of 6,440 MHZ.

In England where it was overcast almost every afternoon and you are low on fuel, because you have been in the air 10 hours you called a “Darkie Station” which was a radio station on the ground (all over England) with a receiving radius of 10 miles. You would call, “Hello Darkie, Hello Darkie, this is Splashboard O Oboe, I need a heading to station 106.” Darkie had all the headings to every field from their particular station, and they would give you, “Splashboard O Oboe take a heading of 273 degrees for 7 minutes.” You then flew that heading and when at position, he let down his airplane through the overcast, and there was your field.

The radio set is remote controlled by a switch box for each channel a knob to push. On the picture a replica controll box is used. But the whole unit is working. Supply voltage is 12 volts, althoug also 24 volts systems exist. Which indicates that the 12 volt version is an earlier one.


Transmitter receiver TR 1196 a

Left the connection for the oxygenmask earphones and microphone. In the front the crystal types. At the right the replica remote control box, for choosing one of the four channels and controlling the transmitter.


Inside the unit.


At the right front the alternator power supply. Behind the receiver. To the right the transmitter.


In front a good view on the crystal board of the transmitter.


In front the earial- and ground connection and the type plate. Also the Air Ministry mark. The white earia is a modification chart.


Left the transmitter with HF earial coils, for each channel one coil. In the mid the four tuning knobs for pre tuning the HF stages of the receiver for each channel.


An overview of the chassis.


A side view.


A nice paper layout picture  inside of the housing. It showes the components layout of the transmitterpart for service.