JLH 10 Watt class A amplifier - Page 157 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 22nd January 2007, 08:34 PM   #1561
diyAudio Member
 
Join Date: Sep 2006
Hi Chris ma

I think if you provide a way of limiting the volts and amps you can try just replacing transistors and resistors that look dead.

I would suggest you want to take a look at the VAS too - if your upper output device went skywards then maybe it took the VAS/driver with it....

maybe some protection is needed for the VAS?

cheers
John
  Reply With Quote
Old 23rd January 2007, 02:05 AM   #1562
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Hi John,

Vas, do you mean Q3(BD139)?
__________________
The Butcher
  Reply With Quote
Old 23rd January 2007, 09:57 PM   #1563
diyAudio Member
 
Join Date: Sep 2006
Hi Chris ma

I suppose it isn't really a VAS as it works as a voltage-and current stage (VACS)? but yes, that's the transistor to check.

cheers
JOhn
  Reply With Quote
Old 27th January 2007, 02:28 PM   #1564
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Default Second Breakdown

The BD139 checked out ok, but I have to put a new one in now. Very difficult to work on this one in a tight spot.

These 2 Ohmite 0R1 resistors R13, R15 in their damaged state see pic.

Three out of four Mj21194 output transistors were damaged. The Q2, Q2A, Q1 were damaged, Q1A is the only one survived.

I gathered it was because through the years of usage I didn't maintain it by go around and re-secure all mounting screws of the output transistors. The stress of the heat had lossen up the screws and slowly the contact for heat transfer was diminished that lead to this failure.
Attached Images
File Type: jpg p1270247.jpg (51.1 KB, 954 views)
__________________
The Butcher
  Reply With Quote
Old 27th January 2007, 02:40 PM   #1565
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Default Fixing it

For the time being I have replaced the damaged parts with what I have in hand just to try things out.

2 MJ21194 and 1 2N3005
1 Ohmite 0R1 25W thick film power resistor as R13
1 NTE 0R1 2W carbon power resistor as R14
1 BD139 as Q3

using the variac and bring up the voltage checking the Iq current and DC offset. This pic is taken 2 minutes after switch on with full power. This time I am aiming to set the Iq at 138MV across R13.
Attached Images
File Type: jpg p1270243.jpg (71.3 KB, 1075 views)
__________________
The Butcher
  Reply With Quote
Old 27th January 2007, 02:44 PM   #1566
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
This 2 CCS version is so easy to adjust the DC offset and Iq current. The power on from cold to after an hour effect on Q3 has very steady effect on DC offset and the Iq current has changed from 136MV to 139MV from stone cold in an hour. I am very please with that.
Attached Images
File Type: jpg p1270244.jpg (72.4 KB, 963 views)
__________________
The Butcher
  Reply With Quote
Old 27th January 2007, 02:49 PM   #1567
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
See the replaced R13(the thick film) and R15(the grey one). using VR1 and VR2 to set bias and DC Offset. The brown hook up wire is connected to the test plug close to the speaker output terminals for easy Iq checking.
Attached Images
File Type: jpg p1270246.jpg (53.3 KB, 931 views)
__________________
The Butcher
  Reply With Quote
Old 27th January 2007, 02:53 PM   #1568
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Have to wait another hour before I connect it back to the system to see if the speakers were damaged. I hope they are ok
Attached Images
File Type: jpg p1270245.jpg (54.4 KB, 901 views)
__________________
The Butcher
  Reply With Quote
Old 27th January 2007, 03:01 PM   #1569
mikelm is offline mikelm  England
diyAudio Member
 
Join Date: May 2003
Location: England
Send a message via Yahoo to mikelm
I glad u keep the fire extinguisher handy ...
  Reply With Quote
Old 27th January 2007, 03:04 PM   #1570
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Quote:
Originally posted by mikelm
I glad u keep the fire extinguisher handy ...

Always with fear and respect when working and in our case playing with fire literally
__________________
The Butcher
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
20 Watt Class A amplifier JOE DIRT® Solid State 8 31st January 2012 11:41 PM
JLH 10 Watt class A amplifier DomKo Solid State 3 18th November 2003 06:32 AM


New To Site? Need Help?

All times are GMT. The time now is 03:08 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2