This is the schematic symbol of an old radio tube from the 1940´s. It´s the UBL1 Duodiode-Output Pentode. electronic radio tube ubl1 Radio Tube UBL1
This is the schematic symbol of an old radio tube from the 1940´s. It´s the UCH4 Triode-heptode. electronic radio tube uch4 triode Radio Tube UCH4