Sophie Electric

Sophia Electric™ S.E.T. Princess™ 300B Mesh Electron Valves for 300B Amplifiers

Sophia Electric S.E.T. Princess 300B mesh plate valve is the upper class model of the current 300B line (globe shape is still in production). This new valve is using the same 300B plate (as the globe 300B) with stronger plate structure learned from making the original princess valves. It is a true 300B valve. It will work with all 300B amplifiers (Western Electric 300B direct replacement).

The glass enclosure was from the Princess 206 valve for its unmatched sonic beauty. The shape of glass enclosure does make a major difference. Just thinking of violin's shape, if it gets changed to triangle, the sound character of violin will change for sure.

Sophia Electric engineers have conducted many hours of audition and comparison. In the end the current shape of Princess valve glass enclosure is the most preferred choice sonically. It has more volume and more curved than the old ST. It is not the old ST came back rather it is a carefully crafted, researched new 300B model. The result is a 300B mesh plate valve with super clarity, low distortion and out of this world mid range fullness and liquidity. High frequency extension and sweetness is the first thing you would hear.

Note: S.E.T. Princess 300B valve models are proprietary products of Sophia Electric Inc. Due to popularity of these Princess 300B products, there are many look alike (or early ST model) in the market trying to get a share of success from those who can be easily switched.


  • Nominal operating conditions and parameters:
  • Filament voltage

    5,0 V *

  • Nominal filament current

    1,2 A

  • Plate voltage


  • Grid voltage (AC filament)

    61 V **

  • Grid voltage (DC filament)

    58 V ***

  • Plate current (AC filament)

    60 mA

  • Plate current (DC filament)

    62,5 mA

  • Grid to plate transconductance

    5700 Ω

  • Amplification factor


  • Grid current

    0.05 µA

  • Plate resistance

    700 Ω

  • Limiting Operation conditions for safe operation-nor simultaneous ratings:
  • Maximum plate voltage

    450 V

  • Maximum plate dissipation

    40 W

  • Maximum plate current of average tube for fixed grid bias

    70 mA

  • Maximum plate current for manually adjusted grid or self-biasing circuit

    100 mA

* - AC filament supply or direct-current filament supply.
** - AC filament supply is used. The grid and plate returns should be connected to a center tap on the secondary of the filament transformer.
*** - DC filament supply is used. The grid and platter returns are connected to the negative end of the filament.

Sophia Electric™ S.E.T. Princess™ 300B mesh tube plate curves
Sophia Electric™ S.E.T. Princess™ 300B mesh plate valve curves
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Option 1: Premium matched pair with one year warranty (Ceramic base).

Option 2: Premium matched pair with 30 days warranty (Ceramic base).

Option 3: Premium matched pair with one year warranty (Black base).

Option 4: Premium matched pair with 30 days warranty (Black base).

All prices include VAT.

Orders and warranty