At your risk. Potentially lethal voltage. High intensity sound can cause irreversible hearing damage.
Testing with RL=12Kohms has been briefly described on a recent post.
Changing to RL=100Kohms while keeping the output transformer connection to 5:1 surprisingly worked with great sound. And even greater when changing the transformer connection to 10:1.
The sound was big, loud, with great detail and smoothness, although not as loud as when RL=12kohms. Such amplifier operating with just 28V at the anode is great news since connecting the anode directly to the output transformer and removing the RL and coupling capacitor would make the amplifier to operate greatly with just three 9V batteries in series at great efficiency. But the output transformer would have to have an airgap. Ia is just 200uA, could it get away without need for airgap?
This is great news for this amplifier where nothing is connected to the control grid except the music signal through the input coupling capacitor. The electron tube negative bias by emitted electrons is reduced by anode field penetration in the right amount for the tube to settle at the anode potential of 28V. The voltage drop at RL=100KOhms was measured to be 20V. This means Va=28V and Ia=200microamperes which looks great for extremely low noise operation (see for example legendary condenser electron tube microphone schematics).
SO let's start building a 3 stage battery powered RIAA moving magnet or moving coil preamplifier or a few stage low noise microphone preamplifier powered by batteries, of low power consumption and great sound.
And perhaps JFET equivalents to compare.
Transformers both at input and output.
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