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A-4 HUD Cathode Ray Tube

Technical Information

Catalogue No: C0421
Category: Head-Up Display [HUD]
Object Type: Module/Sub-Assembly/Component
Object Name: A-4 HUD Cathode Ray Tube
Part No: G-0528-J2
Serial No: 64964
Manufacturer: Rank Electronic Tubes
Division: Unknown
Platform(s): A-4 Skyhawk
Year of Manufacture: 1976
Dimensions: Width (mm): 73
Height (mm): 73
Depth (mm): 170
Weight (g): 165
Location: Cupboard CA (CRTs) [Main Store]

Mf No. G-0528-J2
Ser No. 64964
Date Code 7631
Mod Status A+CN45117
Buyers Part 27489
Assy. 229-003618


The deflection yoke was probably supplied by Muirhead but this and the Matching Card were separate items in the early PDU. This CRT shows a resistive helix in the beam focusing region which indicates it has the "monocon" gun design; this was found to have significant disadvantages in HUD applications and was abandoned for production HUDs.

The success of the A-7 Corsair HUD was followed by a system for the H, M and N variants of the McDonnell Douglas A-4 SkyHawk. About 465 systems were delivered, from about 1970 to 1978 to the U.S and elsewhere. The system was distributed into the Pilot’s Display Unit (PDU), Video Signals Unit (VSU), High Voltage Power Supply (HVPSU) and the Electronics Unit (EU). It was recognised that all of the information used in the weapon aiming calculations was already being supplied to the HUD to draw the symbology format for the attack phase. A modified interface design, faster logic and expanded store in the waveform generator gave a very effective and self-contained, greatly improved, gun, bomb and missile sight and aiming system which could be installed in many different existing aircraft. Most importantly: because the unit had its own highly capable A to D interface, it could use the existing sensors, gyros, etc. in any aircraft without requiring major internal systems modifications in the aircraft.

As only one display and one weapon aiming format were required simultaneously the HUD Processor speed was found to be adequate for both tasks. An Air to Air gun aiming and a CCIP bombing mode were provided initially.

The HUD Weapon Aiming Computer HUDWAC allowed a precise calculation of Lead Angle. The wider dynamic range of the HUD also permits closer matching of the pilot and airframe kinematics for target acquisition and tracking. This was a big advantage over even the most sophisticated Gyro Gunsight. It was now possible to give displays with better visualisation to the pilot with bullet line or tracer line and these ‘line cues’ increased the probability of a snapshoot against crossing targets over the ‘point’ cue fixed reticle. The HUD system for the US Marine Corps’ A-4M Skyhawk attack jet was the first product of this new concept a HUD weapon aiming computer or HUDWAC which proved to be a world first for the Company. In later designs the Program Store was increased to 4096 words and the Data Store to 128 words the weapon aiming capability was significantly increased. Such enhanced systems were flown on the Mirage Milan, the YF-16 and the YF-17. This system finally reached an 8k instruction PROM store.

All HUD CRTs used by Elliotts -BAE Systems have had a deflection coil which magnetically deflects the beam and focussing is electrostatic. The older units designed by Cintel employed magnetic deflection and permanent magnet focussing.

The inside face, on which the phosphor is deposited, is accurately aligned to the mounting flange of the tube to ensure it coincides with the optical module's image plane. For the earliest Head Up Displays the Cathode Ray Tube was supplied to the Company, usually from Brimar (Rank Electronic Tubes), who separately purchased the  Deflection Yoke from a source such as Muirhead and assembled this in-house  within a mu-metal housing. At one time the Company also wound the Deflection Yokes but eventually it was determined that it was much better to have the CRT supplier deliver a fully aligned Tube Unit Asembly with a Matching Card

A-7 HUD: The Tube Unit Assembly (TUA) is a high luminance image source operating in cursive mode. A fine grain P1 phosphor was used

A-4 HUD: The Tube Unit Assembly (TUA) is a high luminance image source operating in cursive mode. A fine grain P1 phosphor was used


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