Results 1 to 6 of 6

Thread: Please advice me how to do 5150 combo bias mod

  1. #1
    Junior Member
    Join Date
    Aug 2017
    Posts
    14
    Thumbs Up/Down
    Received: 0/0
    Given: 0/0

    Please advice me how to do 5150 combo bias mod

    Hi

    I want to mod my 5150 combo. I find out the schematic is different with 5150 amp head.

    Please see the schematic, is this 47k a bias resistor?
    If yes, I should choose 22k or 47k trimmer? And what value resistor ? 10k?

    And I want to add 1ohm resistor to the power tube pin, to check the ma. I did it for vintage Marshall. How can I do it?

    Thank you

    Is img_8451.jpgClick image for larger version. 

Name:	IMG_8451.JPG 
Views:	42 
Size:	49.6 KB 
ID:	44852

    0 Not allowed! Not allowed!

  2. #2
    Supporting Member Jazz P Bass's Avatar
    Join Date
    Dec 2008
    Location
    Wernersville, PA
    Posts
    12,207
    Thumbs Up/Down
    Received: 5/0
    Given: 4/0
    And keep in mind that the 5150 was deliberately designed with a lowish bias in mind.

    If you goose up the current it messes with the 'Resonance' control.

    0 Not allowed! Not allowed!

  3. #3
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,062
    Thumbs Up/Down
    Received: 45/0
    Given: 28/0
    Quote Originally Posted by Jazz P Bass View Post
    And keep in mind that the 5150 was deliberately designed with a lowish bias in mind.

    If you goose up the current it messes with the 'Resonance' control.
    Agreed. IMO, there is nothing to be gained by this mod.

    0 Not allowed! Not allowed!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  4. #4
    Old Timer
    Join Date
    May 2006
    Location
    Cheshire, UK
    Posts
    1,774
    Thumbs Up/Down
    Received: 5/0
    Given: 4/0
    I'm sure you are right. I've deleted my suggested mod.

    0 Not allowed! Not allowed!

  5. #5
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    9,838
    Thumbs Up/Down
    Received: 62/0
    Given: 102/0
    Quote Originally Posted by The Dude View Post
    Agreed. IMO, there is nothing to be gained by this mod.
    How about reduced tube life?
    (I'm sure the tube dealers would disagree with you)

    0 Not allowed! Not allowed!
    Certified Dotard

  6. #6
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    29,876
    Thumbs Up/Down
    Received: 77/1
    Given: 0/0
    Yeah, if you are not wearing out a set of tubes every few months, you must not be rocking.

    0 Not allowed! Not allowed!
    Education is what you're left with after you have forgotten what you have learned.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Head scratcher: 5150 combo bias mod screweyness
    By Gtr_tech in forum Maintenance, Troubleshooting & Repair
    Replies: 17
    Last Post: 12-05-2017, 02:44 AM
  2. 5150 bias mod
    By tedmich in forum Mods & Tweaks
    Replies: 12
    Last Post: 02-02-2016, 02:31 AM
  3. 5150 Block Letter with a strange Bias Mod?
    By Norseman in forum Maintenance, Troubleshooting & Repair
    Replies: 6
    Last Post: 10-18-2013, 05:02 AM
  4. 5150 combo
    By a5150man4 in forum Music Electronics
    Replies: 2
    Last Post: 07-28-2008, 10:25 PM
  5. Replies: 6
    Last Post: 01-25-2008, 01:43 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •