We present a description of the originally developed 𝛽-spectrometer consisting of two Si(Li)-detectors
with sensitive area thickness above 8 mm and 4𝜋-geometry. The full absorption spectrometer allows for
direct measurements of 𝛽-spectra, disregarding the corrections to response function induced by the electron
backscattering from the crystal surface. In case of 𝛽-spectra of transitions to the excited state of the daughter
isotope additional 3
′′ BGO-detector is used in order to detect the 𝛾-quanta in coincidence with the pair of
Si(Li)-spectrometers