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Old 1st August 2008, 06:31 PM   #1
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Default transistor selection

i have one circuit that operates from 42+42 ac trafo ....the particular amplifier has totally 6 output transistors

at this time i have some many tip 2955 and 3055 do you think that they will do the job ?????

or since they are only 100v rated this is not enough ????
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Old 1st August 2008, 06:58 PM   #2
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You have to look at the safe operating area of the devices. They'll support 100V, but not at full current. Be sure to take into account supply surges if the line goes high and the supply isn't regulated. They're also slow and don't have much gain, so building anything you could call "hi fidelity" will be difficult. Hefty pre-drivers will be needed. Some early amps used those devices, but they weren't known for sound quality. There are way better choices.
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Old 1st August 2008, 07:19 PM   #3
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the thing is that 42+42 ac will provide 56+56 dc more or less so is it ok to operate with 100 volt transitor or not safe ????
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Old 1st August 2008, 09:46 PM   #4
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Sierramike,
I think those transistors are only rated 60V Vce. They will suffer a breakdown with 112V across them. Not safe.
TIP3055
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Old 1st August 2008, 09:58 PM   #5
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Hi Sierramike

...and if you use reactive loads, the load line will drive a path through 60V with some current. Definitely not safe.

Actually the original TIP3055 was rated at 70V (TI; now Bourns).

Others spec. TIP3055 at 60V like the 2N3055. But either way, 70 V still isn't enough. Nor is 100V- you will need something like MJ15003/MJ21194 etc (140V+) devices for your transformer...

cheers
John
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Old 1st August 2008, 10:33 PM   #6
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That's right, John.
I favour the MJ15022/MJ15023 combo.

Sierramike, not all amp designs are tolerant of an arbitrary selection of output devices, even it the voltage ratings are ok. You might want to look in to this.
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