collapse

Author Topic: Lab Series L3  (Read 408 times)

jman

  • Chipper
  • *
  • Posts: 4
  • Chip Points: 0
    • View Profile
Lab Series L3
« on: July 10, 2019, 09:33:46 PM »
Can some one tell me how to set the bias on a lab series L3 Amp.

Jazz P Bass

  • Elite
  • ****
  • Posts: 157
  • Chip Points: 13
    • View Profile
Re: Lab Series L3
« Reply #1 on: July 11, 2019, 11:18:09 AM »
I can't seem to put my finger on the L3 schematic.

If it is anything like the L5/L7, then the bias is fixed.
3mv across any output ballast resistor.
http://www.rru.com/~meo/Guitar/Amps/Lab/schem.html

edvard

  • Regular
  • **
  • Posts: 28
  • Chip Points: 0
    • View Profile
Re: Lab Series L3
« Reply #2 on: July 11, 2019, 09:33:15 PM »
Try this: 
https://mega.nz/#!1ph3CSrY!44oxSuZl6oZOZnnXJ12ikMNFncLJ2-AqZqEFzqUrnKg

Interesting schematic, that L3; it uses a CD4007 strung up to use the top half of it's 3 inverters as P-MOSFETs running the tone controls and another for the reverb driver/master out.
I don't see anywhere that counts as adjustable bias, but I could be wrong...

Jazz P Bass

  • Elite
  • ****
  • Posts: 157
  • Chip Points: 13
    • View Profile
Re: Lab Series L3
« Reply #3 on: July 12, 2019, 12:51:42 PM »
Nice find on the L3 schematic, PE.

It appears that R9 is a variable resistor for idle current adjustment.

Measuring the voltage drop across R16, 0.22 ohm ballast resistor, will give you your bias voltage.

jman

  • Chipper
  • *
  • Posts: 4
  • Chip Points: 0
    • View Profile
Re: Lab Series L3
« Reply #4 on: July 12, 2019, 11:02:11 PM »
Thanks for all the info.

 

* User Controls

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Recent Posts

Peavey Audition Plus by psafloyd
[October 17, 2019, 03:24:56 PM]


Carlsbro Hornet (1970s) by psafloyd
[October 16, 2019, 11:37:28 AM]


Thoughts on the difference in sound between tubes and solid state by jfetter
[October 15, 2019, 07:59:26 AM]


I want to ask a question by Jmatt
[October 11, 2019, 10:47:17 PM]


Does A500 mean 500 ohms or 500k ohm by slimjohnny
[October 11, 2019, 07:11:19 PM]

* Sponsors