Is this a bad scheme

radu8982 · 2nd January 2011, 10:23 AM

Some guys told me this is a poor scheme and I also want your opinion.

wahab · 11:24 AM

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..

jaycee · 2nd January 2011, 11:14 AM

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.

nigelwright7557 · 2nd January 2011, 04:38 PM

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.

jaycee · 2nd January 2011, 07:56 PM

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.

toprepairman · 3rd January 2011, 10:04 AM

Besides, with 70v rails you won't get much over 260 W RMS. (into 8R)

AndrewT · 3rd January 2011, 11:06 AM

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.

2nd January 2011, 11:14 AM	#2
wahab diyAudio Member Join Date: Nov 2009 Location: algeria/france	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 11:24 AM.

2nd January 2011, 04:38 PM	#4
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	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. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

3rd January 2011, 11:06 AM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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. __________________ regards Andrew T.

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2nd January 2011, 11:14 AM	#3
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	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.

2nd January 2011, 07:56 PM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	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.

3rd January 2011, 10:04 AM	#6
toprepairman diyAudio Member Join Date: Nov 2010	Besides, with 70v rails you won't get much over 260 W RMS. (into 8R)

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