The Mic

[KrIVIUM2323]

Transformers looks like edcor's to me.

Active load can vary ( it'll be different eg for a common ground circuit or a cathode follower) , but from what i've seen and deducted from what Analag shown, he used a solidstate CCS as anode load for tube.

As CCS acts like 'theorical' infinite load to the tube it then behave as biasing is defined by a straigth horizontal line on tube curve, giving a max amplification factor ( the max one from the tube used) and low distortion.

You can use other ways to bias than a resistor in cathode like a led or diode. Such ccs can be bjt, fet, depletion mosfet, casoded version ( mix and match),... a cascoded version of depletion mosfet offers stellar performance static and dynamic with minimal signature imho.

Works wonder but often seen as a not 'purist' approach.

 

[Emmathom]

Tr1nsformers looks like edcor's to me.

Active load can vary, but from what i've seen and deducted from what Analag shown, you use a solidstate CCS as anode load for tube.
As CCS acts like 'theorical' infinite load to the tube it then bahave as biasing is defined by a straigth horizontal line on tube curve, giving a max amplification factor ( the max one from the tube used) and low distortion.

You can use other ways to bias than a resistor in cathode like a led or diode.

Works wonder but often seen as a not 'purist' approach.

I think that's what I do but with a CRD instead of a plate resistor (so to force a definite current thru the tube).
Yes I've seen cathode set by 2 diodes in serie (UF4007 for ex.) so to give ~1v or 1,2v

 

[KrIVIUM2323]

What do you call a CRD Emmathom?

 

[Emmathom]

Current Regulation Diode
Same as zener but about current (but rated at max. 100v)
E-152 (1,5mA) E-352 (3,5mA) etc

@thor.zmt taught be to use them and can muuuuuch more debate on that subject...