Cyrus 2 bias, please help - 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 4th February 2007, 03:48 PM   #1
diyAudio Member
 
Join Date: Apr 2005
Location: denmark
Default Cyrus 2 bias, please help

Hi.
I have blown 2 output trans+drivers.
I have change output ti TIP42C and drivers to MJE340 and MJE350.

It plays, but get hot. I have 55mv over the emitter resistor, on the other channel i have 5 mv.
How can i adjust the bias or is there somthing else i can do.

Thanks for reading.

Soren

Scematic: http://www.tcaas.btinternet.co.uk/cyrus1pwr.gif
  Reply With Quote
Old 4th February 2007, 04:04 PM   #2
diyAudio Member
 
Join Date: Apr 2005
Location: denmark
Hi
It's me again.
I have read the post "Cyrus 1 project"
There is a post that show how to put a biaspot in.
It tells that the q.current is 75ma.
It is the same for cyrus 2
If i measure over 1 emitter resistor (0.22 ohm) is 0.75v the right value.
Thanks for reading
Soren
  Reply With Quote
Old 4th February 2007, 06:44 PM   #3
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Soren

Assuming that you have the later 07 version of the Cyrus (the earlier ones had a preset for adjusting the quiescent current) you can adjust the output stage current by varying the value of R81 (or R82 for the other channel).

Increasing the value of this resistor will reduce the quiescent current. For an Iq of 75mA you would have 16.6mV across one of the 0R22 resistors.

The TIP42C is perhaps not a good choice as a replacement output transistor because typically it has a far higher gain than the type originally used (BUV48A) which is actually a high speed switching transistor.

Geoff
  Reply With Quote
Old 5th February 2007, 10:56 AM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
TIP42C is on OK choice as far as gain goes, it will be about the same gain as the original device. However it's a PNP device which will definitely not work. So what did you use really?
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 5th February 2007, 11:45 AM   #5
hacknet is offline hacknet  Singapore
diyAudio Member
 
Join Date: Nov 2002
Location: sg
i have a dead cyrus 2 and i have the same problem. one side keeps burning itself out. the outputs are not dead but the drivers are all in a mess.

ive been scratching my head on how to fix it.
  Reply With Quote
Old 5th February 2007, 11:53 AM   #6
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Did you replace drivers and outputs at the same time? Did you replace the bias transistor?

Have you checked DC offset and stability and quiescent current?
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 5th February 2007, 04:06 PM   #7
diyAudio Member
 
Join Date: Apr 2005
Location: denmark
Sorry, you are right richie00boy. The trans is Tip 41c. Sorry.

Yes, Geoff it is a 07. The resistor r81 is 130 ohm. I will try a pot across the r81.
Do you think, 75ma as q-current is right ?

Thanks for reading.

Soren
  Reply With Quote
Old 5th February 2007, 04:20 PM   #8
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Quote:
Originally posted by sbcellis
Yes, Geoff it is a 07. The resistor r81 is 130 ohm. I will try a pot across the r81.
Do you think, 75ma as q-current is right ?
If your Iq is too high, as indicated in your first post, you need to increase the value of R81. Adding a preset across it will reduce the effective resistance.

The notes I made some years ago when taking some measurements on one of my Cyrus 1s indicate that the quiescent current was about 75mA. I have not seen a service manual so I cannot confirm that this is correct.
  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
Changing grid leak bias preamp to cathode bias bereanbill Tubes / Valves 8 28th March 2009 06:26 PM
WTB Cyrus 1 or Cyrus 2 amplifier monstertrucker Swap Meet 0 20th November 2008 02:04 AM
Stray hum pickup *preamp* cathode R-bias vs. battery bias & 12AU7vs.5687 awedio Tubes / Valves 2 19th April 2008 02:30 AM
Battery grid bias to fixed bias in Toccato? w00t Tubes / Valves 3 2nd December 2007 01:34 AM
Supressed bias amplifier, automatic variable bias system. destroyer X Solid State 2 20th September 2004 11:24 AM


New To Site? Need Help?

All times are GMT. The time now is 05:57 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