Do they have the control and other grids close to cathode?
And they are usually vari μ which seems to help a lot as on the EF183 which sings with just 3V as on the Pleiades V4 microphone preamplifier.
How would they perform with all grids except control grid connected to the anode at very low anode voltage?
The grid can be connected to a few Megohm resistor the other side of which is connected to anode as on other Pleiades V series low level low noise preamplifiers.
The heaters can be underheated.
Examples of tubes: UCH42, ECH42, ECH81...
Or the ECH83 which is already made for 6-12V operation.
Would it then be possible to have a top quality front end with just 1.5V supplying both anode and heaters?
Or perhaps using with 1.5V some tubes that are made for 4V heaters instead of 6.3v...
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