Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on September 21, 2019, 12:40:24 pm
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A Fender 6G3 has two 220k plate R’s to first stage of each channel, bright and normal. The cap across the normal channel’s plate R is .003 in parallel or l believe 3,000p. That value takes out too much treble or too dark, what way should l go, lower or higher valve? And any suggestion what value to try? Without that cap the channel is too bright, .003 too dark.
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If zero is bright, and 3000 is dark, pick a number in the middle. Like 1000.
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The power supply node for that plate resistor looks like ground for audio signals, so a capacitor across a plate resistor like that is about the same as a capacitor from the plate to ground. The larger a capacitor is from the plate to ground, the more high frequencies are cut. The same is true for capacitors across the plate resistor.
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For some reason l keep thinking the opposite for cap values, so if l have a 100p (the same as .0001uf, correct?), going smaller would be going to 500p and going larger would be 47p? Or do I have this backwards? To transpose “uf to p”, move the decimal to the right 6 digits, is this correct? I should know this stuff by now.
Anyway, thanks for the quick answers.
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this might help, not the one I have, but then, I can't find it :icon_biggrin:
http://www.uf-nf-pf.com/uFnFpF-Chart.pdf
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For some reason l keep thinking the opposite for cap values, so if l have a 100p (the same as .0001uf, correct?), going smaller would be going to 500p and going larger would be 47p? Or do I have this backwards? To transpose “uf to p”, move the decimal to the right 6 digits, is this correct? I should know this stuff by now.
If you have the same letter ("p" for instance), a larger number means a larger capacitance. 500p has a larger capacitance than a 47p. If you have different letters ("p" and "u" for instance), convert them so they both have the same letter. Then you should be able to see which one is larger.
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500 is more than 47. Both in raw numbers, and (often) in physical size. And in effect on the circuit.