Autopsy:

• Powersupply 6 volt DC v1.2A with positive tip polarity.

from Wikipedia:

The Speak & Spell line is a series of electronic handheld educational toys created by Texas Instruments that consist of a speech synthesizer, a keyboard, and a receptor slot to receive one of a collection of ROM game library modules (collectively covered under US patent 3934233 ).

The first Speak & Spell was introduced at the summer Consumer Electronics Show in June 1978, making it one of the earliest handheld electronic devices with a visual display to use interchangeable game cartridges.

In 1983, the Speak & Spell was redesigned. The change was even more minute, however, representing nothing more substantial than a redesign of the faceplate graphics.

This version was marketed first in Italian as Grillo Parlante (lit. Speaking Cricket), and then later in the United States and England as the Speak & Spell, and in France as the Dictée Magique again.

source: wikipedia speaknspell.co.uk