STC, Standard Cables and Telephones, the British ITT in Southampton, made its own ARN-21 for the RAF (and Dutch Airforce)
Pictures of all tubes in the British version are in the Virtual Valve Museum
You can download the circuit diagrams here :
ST ARN21 RF circuit
ST ARN21 Video and azimuth circuit
ST ARN21 Modulator and Range circuits
ST ARN21 Power Supply
The standard indicators ID-307 and ID-310, as well as the standard control panels can be used with the STARN21. There were also British versions, like:
Type B82 Control, ref. nr 10L / 2238183 made by STC,
And two types of combined Bearing/Range indicators were made by SMITHS Aircraft instruments:
Type 9547 indicator ref. nr.10Q / 16355 which only has four (115V) synchro’s.
A separate coupler with a lot of synchro’s is needed to convert the tacan
signals to those for synchro’s. This indicator is shown below.
Type 9597 indicator has the Range display below centre, and has built-in
conversion gear allowing direct connection to the (ST)ARN-21
A tribute to its inventor, Sven H. Dodington.
The British decided to make their own AN/ARN21 with all-British components, compatible with the rack mount and cockpit instruments from the ITT-made ARN-21. The British unit, called the STARN21, is made and advertised by STC. The RAF code was ARI.1354
There are many differences, to note some:
The STARN21 has 106 tubes, double function tubes ( like double triodes) are not used. The transmitter cavities are gear driven, not by a chain Therefore, the transmitter is directly behind the front panel, and the modulator is near the range electronic cards. The tuning motor is a 400Hz ac motor rather than a dc motor. Like in the ARN21A, the microswitches are driven by a spiral groove in the turret.
When the range motor must stop, it is left open in the STARN21, rather than shorted as done in the ARN21.