Ad Widget

Collapse

Announcement

Collapse
No announcement yet.

Problem with Mojotone 5F1 build - no sound

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Problem with Mojotone 5F1 build - no sound

    I've got a Mojotone Tweed Champ kit that I finished putting together yesterday morning. I went through the tests to power it up. The pilot light comes on. No smoking or other visible issues. All tubes light up. I'm getting a hum from the speaker, but when I plug a guitar in I get no output.

    I spent all day yesterday going over the wiring, and it looks correct. I've been reading different online forums, that's how I found this one. I've been through some of the posts on this site about people who had the same problem to try to diagnose my issue. No luck so far.

    After taking voltage readings, I have figured out that my problem seems to be with the 12ax7 wiring. I am getting no dcv reading on pins 1,3,6, or 8.

    Here are my readings on the 5Y3 and 6V6:

    5Y3:
    #8: 390v

    6V6
    #3: 373v
    #4: 355v
    #8: 21v

    I appreciate any suggestions anybody has. Here are some pictures:

    Click image for larger version

Name:	IMG_4370.jpg
Views:	1
Size:	197.4 KB
ID:	865651
    Click image for larger version

Name:	IMG_4369.jpg
Views:	1
Size:	139.2 KB
ID:	865652
    Click image for larger version

Name:	IMG_4371.jpg
Views:	1
Size:	161.0 KB
ID:	865653
    Click image for larger version

Name:	IMG_4372.jpg
Views:	1
Size:	168.7 KB
ID:	865654
    Click image for larger version

Name:	IMG_4373.jpg
Views:	1
Size:	170.5 KB
ID:	865655
    Click image for larger version

Name:	IMG_4374.jpg
Views:	1
Size:	171.5 KB
ID:	865656
    Click image for larger version

Name:	IMG_4377.jpg
Views:	1
Size:	176.8 KB
ID:	865657

  • #2
    Originally posted by ss_convert View Post
    ...After taking voltage readings, I have figured out that my problem seems to be with the 12ax7 wiring. I am getting no dcv reading on pins 1,3,6, or 8...
    My fist guess is that you left out the wire under the parts board that connects the positive end of the 8uF filter cap to the junction of the two 100 k Ohm plate resistors that feed pins 1 and 6 of the 12AX7. Take a DC voltage reading at the 8uF filter cap and at the junction of the two 100 k Ohm plate resistors. You could also just measure continuity between those two points with the amp unplugged AND the filter caps completely drained. If you are not sure how to do that then ask for clarification before you proceed.
    Tom

    Comment


    • #3
      That was the problem. Thanks a lot. I don't know how many times I went over the wiring and missed that. I also had the issue others have had with the Mojotone OT. Loud sqealing from the amp. The documentation from Mojotone specifies the red wire should go to the 6V6 and the blue to B+, but it should be reversed. Finally the amp works. I really appreciate the help Tom.

      Matt

      Comment


      • #4
        Originally posted by ss_convert View Post
        ...I spent all day yesterday going over the wiring, and it looks correct...
        That's because the wiring was correct. It was just incomplete. That type of mistake can be hard to find and I'd venture to say that many of us have made the same mistake.
        You did a good job posting the voltage readings and the clear photos. Some people just post "my new amp doesn't make any sound. What could be the problem." Your information really helped narrow down the likely answer.
        Cheers,
        Tom
        Last edited by Tom Phillips; 08-27-2012, 05:31 AM.

        Comment

        Working...
        X