The measurements have been made after the circuit has been operated for one hour at room temperature approximately 25°C.

We have 290 V on the C9 filter capacitor instead of 310 V, maybe because our mains transformer has higher internal resistance than the one used in the Philips EZ81 graphs, which was our reference for the power supply calculations.

In my prototype I have tried using a higher voltage transformer, but the voltages of the circuit were too high, and I finally decided to use the 370DAX.

The output transformer also doesn’t have the same primary winding resistance as the one used in the original circuit. We have

Rp = (310 – 290) / 45 = 444 Ω

in the original transformer versus 350 Ω measured in the 125BSE. It was necessary to change the value of the resistor R8 from 3.9 kΩ to 2.2 kΩ to equalize the plate and screen voltages of V2.

**Total power consumption**

Mains AC total power consumption was 245 mA over 230 V 50 Hz. That’s about 56 watts.

**Voltages**

Point of measurement | Original | 0355st |

TR1 sec with no load | 300 – 0 – 300 Vac | 287 – 0 – 287 Vac |

TR1 sec | 270 – 0 – 270 Vac | |

TR1 fil | 6.3 Vac | 6.3 Vac |

C9 | 310 Vdc | 290 Vdc |

C6 | 290 Vdc | 275 Vdc |

C3 | 210 Vdc | 200 Vdc |

V2a | 290 Vdc | 275 Vdc |

V2s | 290 vdc | 275 Vdc |

V2k | 28 Vdc | 28 Vdc |

V1a | 20 Vdc | 20 Vdc |

V1s | 28 Vdc | 27 Vdc |

V1k | 17.5 mVdc |

**DC Currents** (based on calculations from voltages)

Point of measurement | Original | 0355st |

R12 | 5.13 mA | 6.82 mA |

V2a | 45.08 mA | 43.37 mA |

V2s | 4.92 mA | 6.63 mA |

V2k | 50.00 mA | 50.00 mA |

V1a | 0.21 mA | 0.19 mA |

V1k | 0.21 mA | |

Total per channel | 50,21 mA | 50,19 mA |

**Graphs**

We can calculate the output power

P = U^{2} / R_{LOAD} = 132^{2} / 5000 = 3.48 W_{RMS}

For an input of 100 mV, the output is 132 V. Hence the output is 132 / 0.1 = 1320 times as great as the input.

The gain of V1 is 3.33 / 0.1 = 33.3

the gain of V2 is 132 / 3.33 = 39.64

and the total voltage gain is 33.3 x 39.64 = 1320

When we increase the input voltage, we will have great distortion already in the first tube V1 as you can see in the following graph

**Frequency response**

**Start up voltages**