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Replacing Eye Tubes like 6U5 and 6E5

6U5s are the hardest to find. Frankly, we have more 6E5s than we have 1629s. But if you want to adapt your radio to use a 1629 here's the first two steps: Increase the filament voltage to 12 volts (using the voltage doubler circuit in the diagram) and change the socket to an octal.


You'll also need to make some changes to the AGC/AVC circuit since it takes -22 volts to completely close the "eye" of a 6U5 and only -8 volts to close a 6E5 or 1629. Went to http://www.antiqueradios.com/forums/viewtopic.php?t=3240. At the time, the suggestion was a relatively vague, "put in a voltage divider."

So, we randomly selected a radio from the thirties and drew in a two-to-one voltage divider circuit that should work. We do want to hear from you if you've successfully made the mods.

RCA 86T AGC (original)


RCA 86T AGC (modified for 6E5 or 1629)