This image was acquired from
flickr. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
text World's first Battery electron tube with positive bias portable microphone preamplifier with proximity compensating input transformer. Sound the following spoken words can be heard on YouTube with title ampquotyou are the most beautiful girl have ever seenampquot World's first Battery electron tube with positive bias portable