At your risk. Use all safety precautions. Including a suitable fuse in series with any battery for fire hazed protection in case of short circuit. Protect your ears by all ways possible. Keep volume down.
This is a circuit very similar, practically identical with the Pleiades V6 pre preamplifier operating at 3.6V.
The cathode is connected to ground. The anode, suppressor, screen grid connected together.
A SONY portable CD player line out was connected to grid through a 1μF capacitor.
The battery Vb is connected to anode through the primary of an output transformer. The transformer is a Saratoga Industries, 5KΩ to 600Ω or 4 Ω from a Collins receiver. A few inch full range speaker was connected.
The sound was faint and distorted. When a 10MΩ resistor was connected from anode to grid the sound was much more louder and clearer.
Changing to Vb=18V made a vast difference together with changing Rag from 10MΩ to 5MΩ and then to 1 MΩ or 470KΩ. Anode current was approximately 6mA with Rag=470KΩ. It was found strange that when the 470KΩ was connected from anode to grid, (one end of it to 18V), the grid voltage became 300mV positive but the tube still operated with the some quality of sound. Using 1MΩ (if it is correctly recalled) the grid voltage is slightly negative.
The sound was clean and could be heared in a living room at very low volume and excellent high frequency quality.
This indicates that the EF183 can be an excellent headphone amplifier. And an excellent line amplifier.
Therefore a Pleiades preamplifier can be built with a few stages of EF183 amplifying the faintest sound with low noise and bringing it to pro line level.
It may be possible with just 12V supplying everything.
The front end stage may be better operated with 3.6V including heaters for low noise and maximum information extraction (see other euroelectron posts on the Pleiades V4, V5, V6 preamplifiers.
Further experiments can lead to a nice stereo power amplifier. A step could be increasing the anode voltage. Other suitable tubes may be the 12SK7 which are varimu and high gm too.
The 12K5 has also to be tried as a power amplifier driving a loudspeaker. It operates in an amazing loud and high quality way on the Pleiades Elektra II headphone power amplifier with no components other than one electron tube per channel.
Also an output transformer less headphone amplifier could be made with one EF183 per channel. The relatively high anode current, of the order of a few milliamperes at a low anode voltage indicates a low output impedance. The anode current can pass directly through high impedance headphones just like on the Pleiades Elektra headphone amplifiers. Operation can be at 12V supplying both heaters in series and anodes. A resistor of the order of 1MΩ from anode to grid makes operation possible. Signal is capacitor coupled to grid.
Reference:
On preserving the transconductance of electron tubes at anode potentials as low as 3.6V - euroelectron blogspot
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