Candidate electron tubes or electronic valves for RIAA MM or MC battery powered preamplifiers or microphone preamplifiers or astronomy radio telescopes?

They have to be low mu or amplification factor for operation with low plate or anode voltage. Pleiades lab experience has found gm to be not as important for ultra low noise, low anode voltge, underheated heaters, batteriy powering (in series with protective fuse), Pleiades pull up bias or perhaps even better grid open or at space potential seem more important. So as a summary, low mu, low temperature to avoid secondary emmision, low glow to avoid photoemmision, low plate voltage to avoide secondary emmision by high velocity electron collision, open grid for no grid current seem to be important. Experience with moving coil or ribbon mics which seem much more demanding that MM cartridges due to fact that a mic signal has thousands times more dynamic range that a record playing cartridge signal (see the VU meter needle move not more than 20dB on LPs)... ECC82 are great at 6-12V anode potential with Pleiades bias. Even better for triode connected EF183. Nuvistors too. See older posts for more information. But all above electron tubes consume say 300mA at 6V which is a lot for a portable battery powered preamplifier. For just 10s of milliampers at say 1.4V... CV2269, record low consumption with just one AAA battery in series with fuse for both heaters and anode, see Pleiades v1, V6 etc, has not been tried yet at open grid with a bit higher anode potential. Also 1H4, see Pleiades V6 1H4 open grid, scary resolution and low noise. DCC90, DC90, DC96, DC70, DF97 etc which have not been tried yet at Pleiades lab seem great, promising candidates for pehaps the ultimate in quality and portability. Some references: Open-grid Tubes in Low-Level Amplifiers - Robert J. Meyer - Electronics magagine, 28-volt Operration of Receiving Tubes - C. R. Hammond, E. Kohler and W. J. Lattin both found on the bookElectronics for Engineers - markus and Zeluff. Operating features of the Audion - E.H. Armstrong, the explanation of grid self bias etc.