Sensibly equivalent¶ to:
The VT104 is the UK RAF pre-CV designation for the M-OV PT15. The VT104 HF RF amplifier is a modification of the M-OV civil Type PT5. The principal modifications included raising the voltage of the oxide-coated filament from 4 to 6, fitting a ceramic base cap and making the electrode assembly both lighter and more rugged, as befits airborne applications.
The VT104 was a true pentode whose suppressor grid was dimensioned to inject audio modulation at low power directly from a (transformer-coupled) carbon mike. This eliminated the need for a modulation amplifier: one less thing to go wrong! No wonder the famous T1154 set of WWII was easy to make in vast numbers, light, easy to use and, above all, reliable!
The PT15 was used in WWII within transmitters fitted to bombers such as the Lancaster and Sunderland and many others. The master oscillator for the Marconi 1154/55 Bomber Set was an ML6. More details can be found in the Saga of the Marconi Osram Valve 1005.
The lower anode region with bright shield passing through the lower mica disc. The feint VT104 and the old stores code of 10E/215 are etched into the glass.
The PT15 and oval lozenge indicate that this was made by M-OV.
The rectangular anode with the suppressor grid winding just visible.
The B5 pins set in the ceramic base. Ceramic for airborne work as it does not absorb moisture.
The lower mica disc with the rectangular suppressor grid visible inside the anode.
The wide glass tube envelope is 50 mm in diameter, and excluding the B5 base pins, is 170 mm tall.
References: Private communication & .
Absolute Maximum Operating Conditions¶
Updated March 17, 2019. shape:wide.glass.tube construction:pinch type:pentode age:1930.1940 base:b5 heater:6.0v pins:5 pin:1.g2 pin:2.g1 pin:3.f pin:4.f pin:5.g3 pin:tc.a