The TB4320 from Dario is an audio output pentode with a 200 mA heater for use in series heater chains. This is why the anode voltage is given as 200 Volts as no mains transformer was expected in a universal AC or DC mains set. The valve was introduced in 1936 in both Ct8 and B7 base versions. Sometimes the suffix M would be added for the B7 version and P for the continental Ct8 version. Electrically both versions were identical.
With an anode load of 7,000Ω and a cathode resistor of 400Ω to produce the operating point the output is 3.5 Watts.
The internal structure is obscured in the photograph but with a high power torch it was possible to see the anode as a cylindrical mesh with four side wings at 90 degrees to one another. Two of the wings attached to the support rods.
The envelope is 45 mm in diameter, and including the base pins is 117 mm tall.
References: 1043. Type TB4320 was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated December31, 2012.