While employed by the small San Francisco, California manufacturing firm of Heintz & Kaufman which manufactured custom radio equipment Bill Eitel (amateur radio call sign W6UF) and Jack McCullough (W6CHE) convinced company president Ralph Heintz (W6XBB) to allow them to develop a transmitting tube that could operate at lower voltages than those then available to the amateur radio market, such as the RCA UV-204A or the 852. Their effort was a success and resulted in production of the HK-354. Shortly after in 1934, Eitel and McCullough left H&K to form Eitel McCullough Corp. in San Bruno California.