G8 Touch Tuning

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The G8 Touch Tuning and Remote Control

My thanks thanks go to Rich (Marconi MPT4) who has kindly provided the information for this section.

In the /09 versions of the G8 chassis, a touch tuning assembly replaces the original electrobutton unit. This unit comprises a touch plate with six selection positions. When one of these positions is touched, an integrated circuit operates, selecting the desired tuning voltage, and also turning on a neon indicator behind the selected touch contact.

The switching circuit also provides a starting pulse to a monostable oscillator at the instant the contact plate is touched. the oscillator contains a reed relay in the collector circuit of transistor 1774, this relay short circuits the A.F.C. stage momentarily, enabling selection of the required tuning voltage.

When the touch tuning assembly is hinged forward for tuning purposes, the A.F.C. is automatically short circuited by a switch assembly, to facilitate tuning.

Three DC supplies are provided via socket BB from a sub-assembly on the power supply unit, A 30 volt DC supply for the integrated circuit, A high voltage supply for the touch plate and a supply for the neon indicators.

The 12 volt and 28.5 volt supply for the monostable circuit and tuning circuits respectively are provided from existing supplies via socket C.

Remote Control

A microphone mounted in the front of the cabinet receives an ultrasonic signal from the mechanical transmitter, when the control key is depressed—this signal is amplified and fed to the electro touch unit via pin 6 of plug CC. in the form of a pulse to operate the integrated switching circuit.

Each time the key is depressed, the switching circuit will select the next tuning position in sequence.

The 12 and 28.5 volt supplies are provided from existing supplies via socket C pins 4 and 2 respectively.



The two printed panels containing the touch tuning circuit can be hinged apart after releasing the nylon clip between the two panels—this reveals the print side of the panels, facilitating testing.

The following plates refer: