The "ONLY" thing that matters in dealing with μV. level signals is S/N ratio. It's extremely difficult, but not impossible, to get things quiet enough using tubes. The McHammer setup Frank uploaded uses parallel section 6922s, which boosts gm into territory where success might happen. Frank asked for possible improvements and the much quieter UF4007, instead of the 1N4007, seems obvious to me.
Another tube possibility is the Russian 6C45П (6s45p). Any time you are dealing with such extreme gm, considerable attention must be paid to suppressing parasitic oscillation. Good sized carbon comp. stoppers on ALL grid connections, 100 Ω carbon film stoppers on plate connections, and ferrite beads on the heater power wires are in order. It's only partly in jest that I say the 6C45П is trying to oscillate in its cardboard box.
JMO, success is more likely if Allen Wright's hybrid cascode idea is employed. The use of a low noise JFET on the bottom of the "totem pole" sends the S/N boogeyman running. A single stage gets the signal to a level where it can be "shaped", with ease.
Another tube possibility is the Russian 6C45П (6s45p). Any time you are dealing with such extreme gm, considerable attention must be paid to suppressing parasitic oscillation. Good sized carbon comp. stoppers on ALL grid connections, 100 Ω carbon film stoppers on plate connections, and ferrite beads on the heater power wires are in order. It's only partly in jest that I say the 6C45П is trying to oscillate in its cardboard box.
JMO, success is more likely if Allen Wright's hybrid cascode idea is employed. The use of a low noise JFET on the bottom of the "totem pole" sends the S/N boogeyman running. A single stage gets the signal to a level where it can be "shaped", with ease.
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