Add resistance in series, you get a higher total resistance. Add resistance in parallel, you get a lower total resistance. The maths is simple, but the language can get complicated: does a higher resistance mean a higher load or a lower load. It will normally be an easier load to drive. For that reason I often try to avoid saying 'higher load' because that could mean 'higher load resistance' (i.e. higher resistance) or 'harder to drive load' (i.e. lower resistance).
My understanding: The output tube will see the impedance at the secondary multiplied by its turns ratio. A 8000:8 transformer will mean that when a 100 ohm load is presented at the output, the tube/s will see a load of 100k ohms.
Now when you connect a (say) 32 ohm load across the 100 ohm resistor the load resistance seen by the tube is 24k - this is still far more than the 8k nominal operating load.
The 100 ohm resistor across the output is to prevent accidental open circuit - for example if the phones get tugged hard, or the jack connectors lose contact momentarily etc.
The series resistor (if used) provides some attenuation of output and a slight improvement in idle noise. For example a 2.5W amp puts out about 4.5V. This is about 600mW into a 32 ohm set of phones, and I'd think that is fairly high and may cause ear damage. A good amp will put out about 8-10mV of noise, through a good pair of headphones this may be fairly audible. A series resistor (to taste) can tackle both these issues simultaneously.
Now when you connect a (say) 32 ohm load across the 100 ohm resistor the load resistance seen by the tube is 24k - this is still far more than the 8k nominal operating load.
The 100 ohm resistor across the output is to prevent accidental open circuit - for example if the phones get tugged hard, or the jack connectors lose contact momentarily etc.
The series resistor (if used) provides some attenuation of output and a slight improvement in idle noise. For example a 2.5W amp puts out about 4.5V. This is about 600mW into a 32 ohm set of phones, and I'd think that is fairly high and may cause ear damage. A good amp will put out about 8-10mV of noise, through a good pair of headphones this may be fairly audible. A series resistor (to taste) can tackle both these issues simultaneously.
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