The 410LFT is not given in our references but Thrower mentions the 610LFT six Volt version of this AF triode. The details we have come from the paper label on the valve itself.
The design purpose was as a transformer coupled audio voltage amplifier.
The gettering obscures the electrodes but the label gives useful information.
The manufacturer is given as Fellows Manufacturing Co. Ltd.
The balloon envelope is 46 mm in diameter, and excluding the B4 base pins is 93 mm tall.
