13-09-2014, 09:28 AM
I've received a reply from the same author regarding the last question I posted on another forum:
Posted by me: "Just another question, if say 40 or even 30 ma flows through the xtal then if it's not the grid cathode diode action that passes the above mentioned current am I right in assuming that the current flow circuit is completed by the inter electrode capacitances within the tube along with any external stray capacitance routes?"
Reply: "In the case of this circuit, which I've gathered from your description is a tuned-plate, crystal-grid oscillator (in the manner of a tuned-plate, tuned-grid oscillator), the RF current flow circuit that endangers (or does not endanger) the crystal is through the grid-plate capacitance of the tube--from, and therefore through, the plate circuit of the tube back down through Cgp in series with the crystal (and any capacitances in parallel with it, including strays and the grid-cathode capacitance of the tube in series with impedance of the cathode's RF return).
The situation would be different if the circuit was arranged to be one of the variations (tri-tet, grid-plate, modified Pierce) in which that triode formed by a tetrode or pentode's screen-grid-cathode triode does the oscillating and the tube plate serves as an output port by means of electron coupling (mainly) and capacitive coupling (partially)."
Lawrence.
Posted by me: "Just another question, if say 40 or even 30 ma flows through the xtal then if it's not the grid cathode diode action that passes the above mentioned current am I right in assuming that the current flow circuit is completed by the inter electrode capacitances within the tube along with any external stray capacitance routes?"
Reply: "In the case of this circuit, which I've gathered from your description is a tuned-plate, crystal-grid oscillator (in the manner of a tuned-plate, tuned-grid oscillator), the RF current flow circuit that endangers (or does not endanger) the crystal is through the grid-plate capacitance of the tube--from, and therefore through, the plate circuit of the tube back down through Cgp in series with the crystal (and any capacitances in parallel with it, including strays and the grid-cathode capacitance of the tube in series with impedance of the cathode's RF return).
The situation would be different if the circuit was arranged to be one of the variations (tri-tet, grid-plate, modified Pierce) in which that triode formed by a tetrode or pentode's screen-grid-cathode triode does the oscillating and the tube plate serves as an output port by means of electron coupling (mainly) and capacitive coupling (partially)."
Lawrence.
