30-03-2017, 05:57 AM
(This post was last modified: 30-03-2017, 05:58 AM by Diabolical Artificer.)
Mr Carlson does indeed know his onion's ( though I think he was wrong about heater flash - https://www.vintage-radio.net/forum/show...p?t=122438 ){ he's doing a patreon electronics course at the mo which is good }.... however there is a simpler way to test for the outer foil on a cap as Lawrence imply's. Turn on your scope, turn to lowest setting 50mV or whatever connect cap across lead, IE earth clip on one cap lead, probe tip to tother. Pince cap body with fingers, you'll see a trace/hash/crap of about 100mV amplitude or whatever, now reverse leads. The outer foil is the one with the smaller amplitude trace when connected to the black ground lead.
AFAIK the outer foil goes to the "earthy" end or as Lawrence says the lower Z end of a circuit, which in the case of a de-coupling cap from anode to control grid with a 1 meg or similar R to ground would be outer foil to control grid end. Not sure if I have that right. To find the Z of the output of the first valve you times the dynamic anode resistance in parallel with the anode R by the gain, yes? The Z of the following stage is the grid resistor. so for your bog standard triode gain stage output Z is around 30 - 100k so if it was 79k say and the following grid R was 1meg then the outer goes to the 1 meg end. But if for instance you had an OP Z of 35K and had an grid R of 100k on the following stage then the foil would go to the preceeding stage end.
Not entirely sure about this myself, could someone do some real world example's please?
Andy.
AFAIK the outer foil goes to the "earthy" end or as Lawrence says the lower Z end of a circuit, which in the case of a de-coupling cap from anode to control grid with a 1 meg or similar R to ground would be outer foil to control grid end. Not sure if I have that right. To find the Z of the output of the first valve you times the dynamic anode resistance in parallel with the anode R by the gain, yes? The Z of the following stage is the grid resistor. so for your bog standard triode gain stage output Z is around 30 - 100k so if it was 79k say and the following grid R was 1meg then the outer goes to the 1 meg end. But if for instance you had an OP Z of 35K and had an grid R of 100k on the following stage then the foil would go to the preceeding stage end.
Not entirely sure about this myself, could someone do some real world example's please?
Andy.
