Valve Crystal Oscillator Grid Current

[pwdrive]

I fear I still don't understand it. While not disputing the 40mA figure I just don't know where it comes from.

As I see it there are two sources:-

First there's the Electron stream. But for Electrom Current - Cathode to Anode - that implies that the Grid is the source of the Electrons. More sensible and plausible is an Electron flow from Cathode to Grid, ie a Conventional Current in the usual direction.

Second there's the Inter-electrode Capacitance. However, the 6F6 Data Sheet quotes 0.26pF for Cgk. That will be Pentode connected. So what about a Triode? ECC81 Data quotes 1.6pF. For a 'Modernish' Pentode, like EF91 it's quoted as <0.008pF. None of those figures seem to me to be capable of passing 40mA unless the Voltage and/or the Frequency is very high.

Alan

In all of this thread the only thing to go on as far as I can see for the current is that a 60 ma bulb is in series with the xtal, it could be that only 20 ma (or less?) flows through it to give any kind of illumination?

The 0.26 pf is the Cga capacitance, Cg to the other electrodes including the cathode is 6.5 pf, the largest contributor to the latter I imagine would be Cgk as the control grid will be nearest to the cathode.

Just to ponder, if the xtal was operating in the parallel zone (xtal now inductive) I wonder what the branch current would be through the xtal?

Lawrence.