Results 1 to 6 of 6

Thread: Peavey Valveking 112 grounding explanation

  1. #1
    Member
    Join Date
    Oct 2014
    Posts
    103

    Peavey Valveking 112 grounding explanation

    Hi Guys,
    Have just been asked to look at a Peavey Valveking 112 which is dead. Found one of the Heater bridge rectifier diodes had gone to heaven, replaced it and now amp works again. It however does suffer from some hum and on looking over the circuit board I noticed that the signal lead connecting the pre-amp section to the power amplifier board had been modified, and doing some research I find that this is a common problem.
    But on analysing the schematic I noticed that there appear to be several grounds, eg AGNO2, AGNO1, GNDO,AGND1B etc and they are not connected to one point.
    Is there a member who has extensive experience with this particular model, who can put me straight as to how the ground connections operate in this circuit?
    Your answers will be much appreciated.
    Mike from Australia

  2. #2
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,571
    There are multiple ground circuits and they are all joined one way or another. I recommend you not change them. Hum comes from many sources, so you need to determine where it is coming from. Each type of hum has its own cure. Filter caps do nothing for ground issues, and shielding does nothing for power supply ripple.

    I have to warn you that there are tens of thousands of these things, and a half dozen mentions of something on the internet does not make it common.

    The power supply page shows analog grounds 1 and 2 and ground 0. Also chassis is grounded to earth.

    Ground 0 is GND0 and that is the preamp ground. Now look at the preamp page upper left, the input jack. Note SOME jacks but not all in this amp have an extra little contact below the sleeve one, called chassis. These jacks look like any other jack, but if you pull the board, and look at the face of the jack, there is a little point that bears against the chassis, making contact. What happens many times is someone replaces an input jack with a jack that LOOKS the same, but lacks that point, and so the chassis connection is lost. So looking at that input jack, note that GND0 is connected to chassis at the input jacks.

    After the preamp we have the tone stack, volume, reverb section, and its ground is AGND1. And it connects to chassis at the FX loop jacks by those same little points.

    AGND2 is the power supply ground. Note that both AGND1 and AGND2 connect over to the power tube board through a ribbon, and the grounds there become AGND1B and AGND2B. AGND2B connects to chassis through the External Speaker jack.

    SO ultimately all the grounds connect through the chassis, but not together through the circuit. This prevents ground loops and related ills. If you operate the amp with any of those jacks not firmly against the chassis, as you might during service, of if a jack was replaced with one lacking the ground spike, the ground scheme is broken. Look in the ground circuit of the B+ supply on the power supply page, the two 47 ohm resistors there offer a complete circuit under such conditions, but normally they are shorted across by the chassis.

    If you need a jack, you should be able to get the proper type from Peaveey. I have also made up a chassis connection for such situations that worked. YOu just need to stay aware of it.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
    Member
    Join Date
    Oct 2014
    Posts
    103
    Hi Enzo,
    Thanks for enlightening me! I was rather confused by those 47 ohm resistors and their circuitry but your explanation has remedied my confusion.
    On another note, those diodes in the heater supply chain are rated at only 1A which to my mind would seem a little low and probably why one shorted, I realize that in a bridge circuit they would share the load, but still ???
    Cheers, Mike

  4. #4
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,571
    I am not aware of them being a reliability problem. They power the heaters yes, but remember those heaters are in series, so the same 900ma powers ALL the tube heaters.
    Education is what you're left with after you have forgotten what you have learned.

  5. #5
    Senior Member
    Join Date
    Oct 2015
    Posts
    153

  6. #6
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,571
    What do you want us to see in that thread?
    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. Peavey Valveking 112 question
    By pontiacpete in forum Maintenance, Troubleshooting & Repair
    Replies: 8
    Last Post: 10-19-2016, 02:06 AM
  2. Peavey Valveking 112
    By goldtop5 in forum Maintenance, Troubleshooting & Repair
    Replies: 6
    Last Post: 07-11-2016, 11:23 PM
  3. Peavey Valveking 112 help needed please.
    By BStringThumper in forum Maintenance, Troubleshooting & Repair
    Replies: 14
    Last Post: 06-29-2016, 08:45 PM
  4. Peavey Valveking 112 Mod ?
    By msclford in forum Mods & Tweaks
    Replies: 6
    Last Post: 09-18-2008, 03:07 AM
  5. Peavey Valveking 112
    By goldtop5 in forum Maintenance, Troubleshooting & Repair
    Replies: 4
    Last Post: 12-08-2007, 10:54 PM

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
  •