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Im working on a Marshall 9005 pwr amp. Schem attached. I have two versions of this amp. One shows R21 as a 39k the other shows R21 as a 10k. What difference would this value make in this amp? obviously its changing B+ on the PI. Any ideas?
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Look in the lower right corner of the drawing you linked. In the notes, it says that resistor was changed from 10k in 1990.
Ohms law tells you that at 39k, it will drop more voltage than at 10k. Looks to me like they decided the preamp voltages were too high.Education is what you're left with after you have forgotten what you have learned.Comment
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Yes i did notice that.... i was just wondering what effect .. at least in theory... lowering this voltage would do.... i cant remember if raising B+ on the PI plates increases gain or decreases... i also know it has some kind of efect on frew response i believe...Comment
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...higher voltage equates to:
A) more voltage available to develop voltage-swing over, and thus more gain POSSIBLE but not guaranteed.
B) higher fequency response POSSIBLE, due to lower plate loading....and the Devil said: "...yes, but it's a DRY heat!"Comment
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