Tassie Tiger,
Not quite. (Sorry for noticing your question only now; I am not visiting so much these days.)
What Mr Snook meant was that circuit earth (common) is connected to actual earth (mains earth) via a 10 ohm resistor plus capacitor. His description and photos show that the IEC-earth pin is connected to the chassis at the transformer mounting screw directly under the switch (green wire - not always too clear where it runs). At that point (also not very visible) he connects the resistor/capacitor, with the other end going to circuit common or earth, which also includes the E transformer terminal. Thus the whole amplifier is kind of 'floating', only connected to chassis and IEC earth via that 10 ohm resistor and C.
Originally the circuit was also floating, being connected to chassis only at the Jones plug, in keeping with the philosophy that the chassis should be earthed only at the signal input. There was no mains earth connected anywhere - there was an earth terminal at the pre-amplifier for that purpose, depending on mains arrangements of other ancillaries.
The usefulness of the 10 ohm R+C ....... It does obviate earth loop hum current induction, but then that can also be taken care of with the setting up of the system. 'Safer' - I am not sure what is meant by that. Certainly a 10 ohm resistor is not going to make any difference to your touching the wrong places! The capacitor is more for r.f. purposes; a value of 100nF is often used. I have never used such an arrangement, but have read that some found it a cure for ... can't recall what. As said, there should be no 'earth loops' within a properly set-up system. It is your decision; I have never found that necessary. Perhaps others can comment.
Not quite. (Sorry for noticing your question only now; I am not visiting so much these days.)
What Mr Snook meant was that circuit earth (common) is connected to actual earth (mains earth) via a 10 ohm resistor plus capacitor. His description and photos show that the IEC-earth pin is connected to the chassis at the transformer mounting screw directly under the switch (green wire - not always too clear where it runs). At that point (also not very visible) he connects the resistor/capacitor, with the other end going to circuit common or earth, which also includes the E transformer terminal. Thus the whole amplifier is kind of 'floating', only connected to chassis and IEC earth via that 10 ohm resistor and C.
Originally the circuit was also floating, being connected to chassis only at the Jones plug, in keeping with the philosophy that the chassis should be earthed only at the signal input. There was no mains earth connected anywhere - there was an earth terminal at the pre-amplifier for that purpose, depending on mains arrangements of other ancillaries.
The usefulness of the 10 ohm R+C ....... It does obviate earth loop hum current induction, but then that can also be taken care of with the setting up of the system. 'Safer' - I am not sure what is meant by that. Certainly a 10 ohm resistor is not going to make any difference to your touching the wrong places! The capacitor is more for r.f. purposes; a value of 100nF is often used. I have never used such an arrangement, but have read that some found it a cure for ... can't recall what. As said, there should be no 'earth loops' within a properly set-up system. It is your decision; I have never found that necessary. Perhaps others can comment.
As there is still discussion regarding the use of the cap-to-common capacitance of C2 and C3; this was mentioned in one of my earlier posts, but just to recap: There is some h.f. ringing when viewing a square wave on an oscilloscope without this capacitance. One can eliminate this by placing 18pF capacitors from each KT66 G1 to common to equate the above effect.
But as said before: Checking the response, a lead capacitive compensation gives somewhat better results. I achieved that by placing a 1nF - 1,2nF capacitor across R11. Both the square wave response and actual frequency response in the 60kHz - 100kHz region will show this. In practice it is much of a muchness which method is used, as long as it is one or the other. Again, others can comment.
(And giving unsolicited advice: Do keep C5 away from the quite hot R12. Heat is a particular enemy of electrolytic capacitors!)
But as said before: Checking the response, a lead capacitive compensation gives somewhat better results. I achieved that by placing a 1nF - 1,2nF capacitor across R11. Both the square wave response and actual frequency response in the 60kHz - 100kHz region will show this. In practice it is much of a muchness which method is used, as long as it is one or the other. Again, others can comment.
(And giving unsolicited advice: Do keep C5 away from the quite hot R12. Heat is a particular enemy of electrolytic capacitors!)
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