Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

voltage problem in 400watt amp
voltage problem in 400watt amp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 6th September 2005, 09:58 PM   #1
jojo_tennis is offline jojo_tennis  Egypt
diyAudio Member
Join Date: Aug 2005
Default voltage problem in 400watt amp

hi all
i need help...
i bulid transistor amplifier by mj15003/mj15004 transistors
and i make test when power supply is =+30 / 0 /-30 it is work very good but when i use original power supply = +70 / 0 / -70
the transistors burned
any bady can help me
  Reply With Quote
Old 6th September 2005, 10:18 PM   #2
jaycee is offline jaycee  United Kingdom
diyAudio Member
Join Date: Apr 2004
Location: Norwich, UK
+-70V rails would be 140V across the transistors. This is the maximum Vceo for these devices, and most likely, they can't take it. Use MJ15024/5 or MJ21193/4 instead.

Also this isn't really enough information - what other parts have you used ? Can we see a schematic?
  Reply With Quote
Old 6th September 2005, 10:56 PM   #3
Eva is offline Eva  Spain
diyAudio Member
Eva's Avatar
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Using power transistors near its maximum ratings requires very careful circuit design because any minor oscillation, cross-conduction or thermal runaway issue will kill them. On the other hand, these are very rugged devices and I remember seeing people saying that they were capable to use them with +-70V in a reliable way.

Also, your transistors may be fakes, that would explain the blow-up quite well. In case you don't know what I mean, search the forum for 'fakes', 'fake transistors', etc...
  Reply With Quote
Old 6th September 2005, 11:29 PM   #4
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
voltage problem in 400watt amp
Another question. Did the bias current increase to a higher level? Is the bias stable or does it rise with time (thermal runaway)?
Okay two questions. It's also possible that another transistor was taken above it's ratings. Check them all.

  Reply With Quote
Old 7th September 2005, 12:04 AM   #5
amplifierguru is offline amplifierguru
Account Disabled
Join Date: Aug 2004
Location: Earth
Of course the problem may be simply that the output stage bias currents has increased dramatically with the rail increase from 30V to 70V. Amplifiers with resistive input diff'l tails are particularly sensitive to such changes in supply - their operating currents would more than double sending the output stage bias through the roof!

  Reply With Quote
Old 7th September 2005, 03:33 AM   #6
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
I like anatech's clue, make sure the driver transistors are within spec. They need to be able to take the whole 140 volts as well. A driver breaks down, and it will take out the output transistors.

What is your load impedance, and how many of those MJ output transistors are there in the circuit?
  Reply With Quote


voltage problem in 400watt ampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Great 400Watt Low price amp James82^_^ Vendor's Bazaar 3 22nd March 2007 01:36 PM
how to increase output power on a 400watt amp db junkie Solid State 14 11th October 2005 07:20 AM

New To Site? Need Help?

All times are GMT. The time now is 10:59 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio