Capture from the D3a datasheet ("as triode" section) shows Vg1 as +10V ????
Firstly I would expect g1 to be negative wrt cathode.
Secondly the curves would indicate a bias of 1.5, not 10.
Cathode bias using a 470R with 24mA works out around 11V.
What am I mis-reading ?
D3a datasheet confusion
#2 Re: D3a datasheet confusion
Agree it doesn’t make much sense to me as a way to specify the op point, but that cathode R with that grid volts would work, if the Vb notation means absolute volts rather than relative to cathode? So the grid is at 10v and the cathode is around 11.5?
#3 Re: D3a datasheet confusion
Maybe it gives more stable biasing or something?
#4 Re: D3a datasheet confusion
Oh I see. Thank you that helps. So the datasheet proposes a mixture of cathode and fixed bias. I wonder why.
I know Steve (izzywizzy) of this parish uses the D3a in his phono stage and he uses diode biasing, so grid at 0v cathode at about 0.7 ish I guess (I haven't checked the datasheet for that SIC diode).
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#5 Re: D3a datasheet confusion
With all valves cathode bias allows greater value grid leak resistor often by a factor of ten. Fixed bias therefore means considerably larger coupling cap.
The numbers quoted mean net bias -1.28 but hybrid of fixed and auto. Perhaps necessitated by expected RF environment it designed for, which we don’t know about in our restricted bandwidth vis a vis RF. That and the unstable nature of high transconductance valves per se.
The numbers quoted mean net bias -1.28 but hybrid of fixed and auto. Perhaps necessitated by expected RF environment it designed for, which we don’t know about in our restricted bandwidth vis a vis RF. That and the unstable nature of high transconductance valves per se.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein