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On a 5E3, I see references to a bright and a normal input. On the shcematic, however, everything looks the same on the 2 channels. Both inputs to the respective grids have the same components in the path. The signal path leading away from the triode looks identical to me except for the 0.0005 mica cap on the tone control. What have I overlooked? Also, is there a source that will help me understand the nomenclature of some of the parts: Is the input resistor the 1 meg or the 68K; and what makes a coupling cap a coupling cap?
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Yes the 500pf cap is also across the middle and top lugs of the volume control. When the volume is not at MAX you'll here the "bright". When the volume is all the way up the cap basically isn't there.
The 1meg is called a grid leak. The 68k is called a grid stopper. The 1 meg dictates input impedance of the stage and the 68k is there for stability as it rolls off the very high highs when taking miller capacitance into account. -
Thanks! (NT)
Thanks for the very concise response!Comment
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Concise but;
the 68K resistors are not grid stoppers.... they are part of a voltage divider at the input jacks in order to use and mix the signals on the two jacks at the same time and still have some kind of decent grid load... not grid leak... resistance.
Grid leak is a little more nebulous in description but I guess it's still OK to use it in this context.
Look up contact bias and a mu triode and you'll see some other stuff that is interesting with respect to this subject.Comment
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My bad. So plugging into the 2nd input ONLY, you get a voltage divider of half and an input impedance of 68k. I still think they are grid stoppers that have been wired in a way that makes them perform more than one thing, ie voltage division.Comment
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