Results 1 to 2 of 2

Thread: Crate GT-100H Tube Biasing

  1. #1
    Junior Member
    Join Date
    Nov 2017
    Location
    Cleveland OH
    Posts
    1

    Crate GT-100H Tube Biasing

    Hello all, new to the forum. I own a GT-100H Stealth Tube head and I tried searching for my amp on your forum but didn't find anything. I bought new EL34 tubes to put into my Crate GT-100H Stealth amp I've had since the mid 90's but I cannot find the bias adjustment on the circuit board. Anyone have any experience with these? I called Crate (now Loud Tech Inc I guess) and they couldn't help me. I was referred to a local service center and they couldn't (or wouldn't) give me any info either. Anyone know how to bias these tubes on this amp? I have uploaded the manual and schematic and they do not show the bias points (or I can't find them?). The manual says these can ONLY be done by an authorized service center. Anyone know the trick to biasing the tubes here? Any help is greatly appreciated.
    Attached Files Attached Files

  2. #2
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    9,255
    There is a bias pot called AP1 .
    That said, all they specify is that bias is set to -45V with no further explanation.
    Specifically there are no "current measuring" test points, so I *guess* :
    1) Factory loads these amps with matched tubes, so they set bias once and leave it there.
    Supposedly Service Techs replace tubes and readjust bias as needed, so they donīt feed the need to help end users do it.
    By the way, what thousands of Manufacturers did along the last 60 years; user accessible bias test points are an "extra feature" added to a few amplifiers, not a standard by any means.
    2) again guess Service Techs start with the suggested -45V setting (FWIW Fender specified -52V , period, on many of their amps, and that with 6L6), and if needed fine tune bias using an oscilloscope, not exactly an user friendly system.
    Personally I would check -45V is available at the junction R75/R76 and touch preset only if not.

    If you want a finer , more "modern" adjustment , you will need to add cathode current sensing resistors and use them .
    Personally, unless amp hums with all controls set to zero, one or more tubes get red hot or output is weak and nthin, I would leave as is.
    Or get a scope and use that procedure.
    Or have a Tech do it for you.
    Juan Manuel Fahey

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. >>>>> Roland JC-120
    By gtrcollege in forum Guitar Amps
    Replies: 2
    Last Post: 07-20-2012, 04:50 AM
  2. Crate GT-100H
    By gwoodruff in forum Schematic Requests
    Replies: 3
    Last Post: 07-20-2010, 11:15 PM
  3. Crate V-100h Head Died
    By zman32006 in forum Maintenance, Troubleshooting & Repair
    Replies: 7
    Last Post: 11-01-2009, 12:34 PM
  4. Help need jtm60 amp guru>>>>>>>>>>>>>
    By Jay101 in forum Maintenance, Troubleshooting & Repair
    Replies: 4
    Last Post: 07-07-2009, 09:05 PM
  5. Hey Possum>>>>>>>.
    By madialex in forum Pickup Makers
    Replies: 0
    Last Post: 05-15-2007, 12:36 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
  •