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Old 2nd January 2011, 11:23 AM   #1
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Default Is this a bad scheme

Some guys told me this is a poor scheme and I also want your opinion.
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Old 2nd January 2011, 12:14 PM   #2
wahab is offline wahab  Algeria
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All the transistors have far lower Vce than required,
only the 140 V VCE output pair may survive the voltage,
BUT not the output power if ever it is used at full power
on a 4R load, or even unloaded, as the VBE multiplier
voltage drop is set with a fixed resistance divider which
is unrealistic given the transisors caracteristics dispersions..

Last edited by wahab; 2nd January 2011 at 12:24 PM.
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Old 2nd January 2011, 12:14 PM   #3
jaycee is offline jaycee  United Kingdom
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two pairs of MJ15003/4 on 70V power supplies is guaranteed to blow up when pushed hard.

All of the other transistors, BC557, BD139/140, BD243C/244C are also not capable of working on a total supply of 140V.

The circuit would work if you use say 35v supplies, but then you would not get 500W.
I wouldn't build it.
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Old 2nd January 2011, 05:38 PM   #4
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I would have added a current mirror to the LTP.

Use MPSA42 and MPSA82 transistors as these can stand 150V easily.

I also would have added a safely wired pot to the Vbe multiplier.
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Old 2nd January 2011, 08:56 PM   #5
jaycee is offline jaycee  United Kingdom
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Better to find a design already made for it, than try to modify one that isnt

Besides, 500W into 8 ohms is not really DIY - you will pay more to build it than you will to buy it.
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Old 3rd January 2011, 11:04 AM   #6
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Besides, with 70v rails you won't get much over 260 W RMS. (into 8R)
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Old 3rd January 2011, 12:06 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
we know you have a link to Romania and that this is your second post.

We have no idea what skills and build resources you have.
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regards Andrew T.
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