Multiplied Transconductance Amplifiers

In the heydays of AM radio receivers some tubes were produced having up to 6 grids, called octodes. These tubes can be arranged as a triode and a hexode in a common bulb, with a common cathode. Frank Blöhbaum, never afraid to explore unusual (some would say crazy) topologies, combined a cascoded non-inverting triode section with a common grounded cathode stage to arrive at what is called a Multiplied Transconductance Stage. This article explores MTA topologies with real-life measurements, feedback arrangements and design guidelines for line-level and low-power MTA amplifiers. A future article will focus on MTAs for higher power applications.