3 December 19

The DB-23 was

A: an audio amplifier
B: a dual boom headset
C: an RF preselector
D: a computer data cable connector
Answer is C…Boosts the gain and signal-to-noise ratio of Amateur receivers. 

The Electro-Voice RME DB23 (RME stands for Radio Mfg. Engineers)is a low noise, radio-frequency preselector amplifier which can substantially improve receiver performance in the following amateur bands: 3.5-4, 7-7.3, 14-14.5, 21-21.5 and 26-30 MHz. It utilizes three tubes (3 x 6J6). It operates from 117 VAC 50-60 Hz.
This is a receive-only device. 

Click on the Spec sheet below for a full view