WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Looks to me like the trade mark of Bentley Acoustics. They were a company that supplied valves by mail order but the country of origin was variable. I have for example a Bentley Acoustics 5Z3 that was made by Westinghouse in Canada. I think they re-badged a lot of ex-military valves and also many from other countries like Italy, Germany and Russia. Pinnacle and Z & I Aero were similar companies.