Results 1 to 8 of 8

Thread: '72 Ampeg SVT 60 HZ hum problem

  1. #1
    Senior Member booj's Avatar
    Join Date
    Jun 2008
    Posts
    649
    Thumbs Up/Down
    Received: 6/0
    Given: 0/0
    Rep Power
    12

    '72 Ampeg SVT 60 HZ hum problem

    Polarity switch has no effect. AC plug ground is connected to chassis. the guy took it to the shop I work at and we could not find a problem. then he comes to the shop with his epiphany speaker cab and hooks it up. HUMMMM.... So its intermittent? I think this is a weird problem so I'm posting it. I'll keep y'all informed.

    0 Not allowed! Not allowed!

  2. #2
    Don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    11,724
    Thumbs Up/Down
    Received: 1,602/23
    Given: 4,085/11
    Rep Power
    22
    I've had problems with the shield wire in the wiring harness to the preamp with these, or the connectors.

    0 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  3. #3
    Supporting Member nevetslab's Avatar
    Join Date
    Apr 2010
    Location
    Burbank, CA
    Posts
    1,788
    Thumbs Up/Down
    Received: 646/1
    Given: 1,475/1
    Rep Power
    11
    Quote Originally Posted by g1 View Post
    I've had problems with the shield wire in the wiring harness to the preamp with these, or the connectors.
    THAT ^^^^^^^^^^^. I too have had issues with the shield connections in the wiring harness. Tedious to chase down with all the discrete wiring.

    0 Not allowed! Not allowed!
    Logic is an organized way of going wrong with confidence

  4. #4
    Senior Member booj's Avatar
    Join Date
    Jun 2008
    Posts
    649
    Thumbs Up/Down
    Received: 6/0
    Given: 0/0
    Rep Power
    12
    Click image for larger version. 

Name:	IMG_1465.JPG 
Views:	9 
Size:	1.88 MB 
ID:	55286Click image for larger version. 

Name:	IMG_1462.JPG 
Views:	10 
Size:	1.90 MB 
ID:	55287Click image for larger version. 

Name:	IMG_1461.JPG 
Views:	10 
Size:	1.93 MB 
ID:	55288

    Anybody got a clue on where this mystery hum is coming from? Grounds seem to be solid. Perhaps inside the preamp? Looks like good connections to the plug.

    0 Not allowed! Not allowed!

  5. #5
    Old Timer Leo_Gnardo's Avatar
    Join Date
    Sep 2012
    Location
    Dogpatch-on-Hudson
    Posts
    6,392
    Thumbs Up/Down
    Received: 1,409/21
    Given: 1,195/0
    Rep Power
    14
    Some more clues might be found here:

    http://archive.ampage.org/threads/6/...um_long-1.html

    Also, boost or cut midrange often brings in some hum, which is picked up by the inductor in the midrange circuit. Some relief might be found by rotating the inductor to a position where it picks up minimum hum when mids are cut or boosted.

    0 Not allowed! Not allowed!
    Enjoy. Every. Sandwich.

  6. #6
    Supporting Member loudthud's Avatar
    Join Date
    May 2006
    Location
    Near Dallas Texas
    Posts
    3,537
    Thumbs Up/Down
    Received: 220/0
    Given: 113/1
    Rep Power
    18
    Does this version have a Hum Balance pot ? Is this more of a buzz type hum, or a low Organ note type hum ? Check the pot if it's the low organ note type.

    2 Not allowed! Not allowed!
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !

  7. #7
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    6,314
    Thumbs Up/Down
    Received: 1,213/1
    Given: 943/1
    Rep Power
    16
    ^^^^^^ That. I've seen the pot burned up in several of these. I'll usually remove the pot and just install a couple of 100 ohm resistors for the artificial center tap.

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

  8. #8
    Senior Member SoulFetish's Avatar
    Join Date
    Jan 2016
    Location
    Massachusetts
    Posts
    1,203
    Thumbs Up/Down
    Received: 406/1
    Given: 346/0
    Rep Power
    6
    Quote Originally Posted by The Dude View Post
    ^^^^^^ That. I've seen the pot burned up in several of these. I'll usually remove the pot and just install a couple of 100 ohm resistors for the artificial center tap.
    Yup.

    0 Not allowed! Not allowed!
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Problem with my Ampeg V2
    By Foxfire in forum Maintenance, Troubleshooting & Repair
    Replies: 18
    Last Post: 08-27-2012, 02:39 PM
  2. Ampeg SVT 4 Problem
    By Street 760 in forum Music Electronics
    Replies: 4
    Last Post: 01-31-2011, 09:41 PM
  3. Ampeg B-2RE problem
    By kevindquill in forum Maintenance, Troubleshooting & Repair
    Replies: 5
    Last Post: 10-07-2010, 08:49 AM
  4. Problem with my 81 Ampeg V3
    By deanamite in forum Guitar Amps
    Replies: 4
    Last Post: 10-06-2010, 02:44 AM
  5. Ampeg b-100 problem
    By machinegunstudios in forum Maintenance, Troubleshooting & Repair
    Replies: 4
    Last Post: 10-15-2009, 01:04 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
  •