Type A1961M
Intercom Amplifier
The transistorised version of the older A1961 intercom amplifier. These two amplifier types share the same enclosure and connections, and are directly swappable.
Used in multi-crew aircraft of the Cold-War era, such as Lightning T5, Vulcan and Canberra, with aircrew using dynamic microphones.
They formed the heart of intercom systems, and allowed integration with other aircraft communication and navigation systems.
It will deliver 1Watt into 10 standard UK NATO headsets / helmets connected in parallel - these are 150 ohm headsets. 2 to 20 headsets can be driven without distortion due to substantial negative feedback.
The amplifier has a flat frequency response between 300Hz and 5kHz, but is sharply attenuated outside these limits.
Circuit Diagram
The input stage allows the outputs of two UHF / VHF radios (or other devices such as navigation, or warning) to be mixed with the crew microphone signals.
Power Supply
The amplifier drawings state 24Vdc supply, but most aircraft suppies are 28Vdc. This is evident in the Lightning T5 wiring diagrams:
Notes
NSN: 5821-99-223-7295 | Manuals: A.P.2876E, Vol.1 or A.P.116N-0105-1 | Also referred to as A.1961M
Wanted
I'd quite like to find one of these amplifiers to photograph and document in detail on this site, including sound recordings to give the audio experience too. If anyone has one available, I'd be interested to talk, thanks.