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Old 12th December 2008, 05:29 AM   #11
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im gonna replace all fets again this time with the 3205's . before the fets went the amp didnt draw that much current. it was idling fine think the reason they went i didnt have them solderd on the mesha board ver good couple of them were loose. wondering how do i cure the hiss in that transformer.
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Old 12th December 2008, 05:49 AM   #12
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Solve the rest of the problems and the hiss may go away. If it doesn't, the problem may be loose windings. Moving them or applying a fixative to them may stop the noise.
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Old 24th December 2008, 04:07 AM   #13
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ok i put in new 3205 in the supply went to power it up and it tries to draw 40 amps of current so i checked the 3205's and all outputs everything is cool still makes the hiss wondering where do i go next. also checked all gate resistors all read 10.1 ohm
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Old 24th December 2008, 04:14 AM   #14
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Did you check the driver transistors (mpsa06/56)?

To confirm that you have a good connection on all of the gates of the PS FETs, measure from one gate leg (near the body of the transistor) to the next FETs gate leg. For all of the transistors in each bank, you should read ~2x the gate resistor value. If you don't, you have an open trace or a bad solder connection. There are 4 banks of PS FETs in this amp.
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Old 24th December 2008, 04:40 AM   #15
a.wayne is offline a.wayne  United States
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Fosgates where always Smokey amplifiers , my first in 78 would not go more than a month between repairs , my last in 86 was much better, by then i had switched over to soundstream and there first generation true class a amplifiers, still have them today .....
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Old 29th December 2008, 02:38 AM   #16
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i checked all 56's and 06's all check fine. Also checked the gate resistors from 1 gate leg to the next i get 20 ohms on all of them . also put meter leads in the positive and negative terminals everything checks fine. when i try to power it up it draws 40 amps of current wondering what shouldi check next
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Old 29th December 2008, 02:57 AM   #17
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If you don't have any shorted outputs, you need to disconnect the power supply from the audio section. They are connected by the red and black twisted pairs. BEFORE you attempt to desolder them, discharge the caps by shorted between the red/black wires with a resistor or dummy load (with insulated leads). The caps can remain charged for a VERY long time and may have 100+v on them. Desolder them from the power supply end of the wires.

With those 4 wires disconnected, does it draw excessive current?
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Old 30th December 2008, 02:21 AM   #18
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I unhooked the red and black wires all 4 of them and tryed power it up still draws 40 + amps of current wondering what do i check next. so now i know its a power supply problem
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Old 30th December 2008, 07:37 AM   #19
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If you connect only ground and remote (no B+), do you get a clean square wave on the gates of ALL of the power supply FETs?

If you do, 1 of the transformer's is likely shorted. With a limiting resistor in the B+ line, power the amp up (including B+) and twist, push and pull the transformers to see if the current draw intermittently decreases.
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