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Description:
The Edison Dual Purpose Unit could function as a valve detector (to drive headphones) or used as an amplifier when connected to a crystal radio and a loudspeaker. PO Reg No. 4547.
4 Pages, 1MB download
![Edison Bell Valve Detector and Amplifier, Dual Purpose Unit (DPU)](https://www.valve-radio.co.uk/wp-content/uploads/2022/01/17-656x1024.jpg)