cambridge p60 is alive - 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 14th October 2007, 12:05 AM   #1
dukep is offline dukep  United States
diyAudio Member
 
dukep's Avatar
 
Join Date: Oct 2007
Location: North Carolina
Cool cambridge p60 is alive

Well it has been years waiting patiently in a box. the pre-amp section is crippled due to corrosion of the pots, so I've decided to be an amp only. My vintage soundcraftman as the preamp.

I rebuilt the power supply (new caps/ rectifier/ bypass caps)
Then some flashy banana plugs and phono inputs. test.. hmmm-- sweet!

I had forgotten how well this amp performs. This cute little amp has a new life.

Anyone out there know the bias setting? I used the standard 5mv across the emitter resistor or ? (note:I don't have a distortion analyzer- but a good ear and 0-scope.)

Heatsink is a bit small and disjointed (4th transistor is on a 2nd section). It runs hot (after jamming 30min) and the 4th transistor runs cooler than its complement. Anyone know what the original specs were?
__________________
Duke ~ dukescreations.com
  Reply With Quote
Old 14th October 2007, 09:15 AM   #2
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
output stage is what?
Integrated darlington, or two stage EF, or two stage CFP, or somethng else?
5mV across the emitter resistor sounds like it may be CFP.
__________________
regards Andrew T.
  Reply With Quote
Old 14th October 2007, 12:34 PM   #3
dukep is offline dukep  United States
diyAudio Member
 
dukep's Avatar
 
Join Date: Oct 2007
Location: North Carolina
Default to-3 outputs

This has a pair per channel, mj802 & mj4502; bjt's
100v 30 amp outputs. Rail voltage runs +/-39v from a toroid xformer.

I slowly turned it up from 2mv to 5mv. the sound and crossover distortion improved.
__________________
Duke ~ dukescreations.com
  Reply With Quote
Old 15th October 2007, 05:15 AM   #4
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
Hi,anyone here got any information on the P50 MKII???
  Reply With Quote
Old 15th October 2007, 03:21 PM   #5
dukep is offline dukep  United States
diyAudio Member
 
dukep's Avatar
 
Join Date: Oct 2007
Location: North Carolina
Default found the schematics

This helped me, maybe others too. The bias is set at 7ma q-current.
measure current with + fuse out (~20), turn until x+7ma.

Then do the other channel.

and maybe applicable to the p50.
__________________
Duke ~ dukescreations.com
  Reply With Quote
Old 16th October 2007, 05:15 PM   #6
diyAudio Member
 
Join Date: Aug 2005
How do you know the current(which is what is the issue here) without knowing/telling the value of the resistor?
The P50 has TIP35/TIP36 output em followers,but with a little unusual arrangement of the resistors(0.15ohms).They are placed in the collectors and directly connected to + and -
I wish there was a standard using a 1ohm resistor to measure the current,and then the resistor is shorted in normal use.Would create a lot less errors,I believe.
  Reply With Quote
Old 18th October 2007, 10:58 PM   #7
dukep is offline dukep  United States
diyAudio Member
 
dukep's Avatar
 
Join Date: Oct 2007
Location: North Carolina
Default bias never easy

I agree.

I usually measure the voltage across the emitter resistors which is much safer than pulling a fuse.
When you know that 7ma should flow through the emitter resistor, and it is 0.15 ohm ( this amp is a bit weird, with collector and emitter resistors). Run the calculation,, v=ir carry the zeros .....

I read the current by placing the multimeter on the amp output and emitter pin of the transistor, Mr. Mj802. .. but higher is not necessarily bad. Just closer to class A, but check the heat!
I'll be changing the heatsink anyway because my speakers are 4ohm.

I was once instructed to use a distortion analylizer ($$$) for a SAE amp. Don't have one. JUst tweek it and test, listen, and feel the heat. As we know, it is highly subjective. That's why it has us dIY's working so hard.

pwd
__________________
Duke ~ dukescreations.com
  Reply With Quote
Old 3rd December 2007, 04:36 AM   #8
diyAudio Member
 
Join Date: Dec 2007
Exclamation New Vintage Cambridge Audio site!!

Hello.
I've, in the past seen some requests for info on the original Cambridge Audio gear - have P50 MkII / P60 / T55 / R50 myself - not all working (...).
Just over a week back I created a Google Groups site.

At present I've donated my Cambridge Audio P50 Service Manual - 80pp - contains all the info on the 3 types of that amp - there's a P60 circuit diagram - info/reviews on these + the T55 & R50 loudspeakers.
Stan Curtis is a member too!!

Hope that the site will be useful for info - also maybe some discussion on Cambridge Audio gear!

http://groups.google.com/group/vintage-cambridge-audio

All best
Frank
  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
JBl GTS600, amplifier wanted! Dead or Alive, Alive if it can be helped:) Paradise_Ice Swap Meet 11 10th June 2013 02:02 PM
My new amp...is Alive!!! SpeakerScott Solid State 5 31st January 2009 04:15 PM
DAC alive till Digital Source 88 25th May 2004 09:35 PM
My first Nos dac is alive! setmenu Digital Source 23 23rd April 2004 01:59 PM
Its nearly alive... Jye Chip Amps 20 15th December 2003 11:06 PM


New To Site? Need Help?

All times are GMT. The time now is 10:12 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