U1035

U1035 is a low‑power vacuum tube that was developed in the mid‑1960s to serve as an audio amplifier and a weak radio frequency (RF) transmit stage. The device is packaged in a 12‑pin dual inline package and employs a negative‑grid triggering circuit that offers stable operation over a wide range of load currents. When driven with a cathode voltage of about 250 volts, the U1035 can deliver approximately 1.5 watts of RF power between 2 and 4 gigahertz and about 5 milliwatts of linear audio power.

The tube was most commonly used in handheld ham radio transmitters, simple portable broadcast transmitters, and in some marine navigation radios such as depth‑sounders and echo‑sounders that required a compact and inexpensive power source. Production ceased in the early 1980s as solid‑state devices entered the market, but the U1035 remained popular for a time because of its rugged construction and reliable performance. Under laboratory conditions the mean time between failures exceeded 20,000 operating hours, and many modern restorers of vintage audio and radio equipment still seek U1035 tubes from surplus vendors. Technical details, including schematic symbols and performance curves, are published in Telefunken’s Technical Series 401B and in 1966 radio‑electronics handbooks.