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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 box anode with fixing struts passing between the two sheets forming the anode.

The glass distorts the view of the grids. The oxide coated filament can be seen in the centre.

The wide glass tube envelope is 51 mm in diameter, and excluding the B5 base pins, is 174 mm tall.

References: Private communication & .

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.