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11-23-2008, 06:54 PM
| #1 |
| Junior Member Join Date: May 2008
Posts: 12
| Marshall Plate Voltage Schematic Mystery
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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11-23-2008, 06:55 PM
| #2 |
| Junior Member Join Date: May 2008
Posts: 12
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11-24-2008, 10:45 PM
| #3 |
| Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA
Posts: 10,354
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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. |
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11-25-2008, 03:58 PM
| #4 |
| Junior Member Join Date: May 2008
Posts: 12
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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...
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11-27-2008, 08:23 PM
| #5 |
| Senior Member  Join Date: Oct 2007 Location: Tucson, AZ
Posts: 431
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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!" |
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