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Need help repairing and/or modding B&K amp

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  • Need help repairing and/or modding B&K amp

    I picked this up used several years ago and don't specifically recall ever hooking it up. I was hoping to replace my underpowered shop amp with this one but it appears to need some TLC if that's going to be the case. I'm a hack when it comes to electronics repair but I've had some success over the years without setting anything on fire.

    Make/Model B&K AV-6.5.4 (appears to be identical to the B&K VMR-6.5.4, Google search yields much more info for this model)

    https://www.manualslib.com/manual/14278/BAndk-Vmr-6-5-4.html

    Amp is rated to 60x6 or 120x3

    Issue: won't power on, power indicator LED fails to illuminate

    Verified continuity for all fuses

    For whatever reason, one of the power input leads seems to have come off the bus it was connected to. The bus connections are made via 1/4" spade terminals. The disconnected lead was found close to the bus and it appears that it would have most likely went to 1 of 2 bus connections that then go to the transformer. I'm guessing that a more experienced person could readily ID which transformer connection is the correct one. I've attached a pic of the bus as well as "schematic" of the area in question.

    The second issue I'd like help with is bridging the amplifier. The manual states:
    “Channels 1&2, 3&4 and 5&6 are available for bridging in order to provide 3 channels capable of providing 120 watts r.ms. into an 8 ohm load. However, due to the relative complexity of the modification it is recommended that this conversion be carried out by your dealer’s technician or at the B&K factory in order to comply with warranty requirements. For more information on bridging the VMR-6.5.4, please contact your dealer or B&K directly.”

    B&K as we used to know it has been out of business since 2016. A Google search for how to bridge these seems to yield nothing but several other people asking the same question over the years. The only obvious thing I've found by poking around in this thing is 3 capped wires marked "BR" on the board. There is one wire on the left amp board and two wires on the right amp board. I've attached a pic of one of those wires on the board.

    I do appreciate any help offered. This does appears to a well constructed amp and it'd be great to hear it run again.


    Attached Files
    Thanks,
    Aaron

  • #2
    I'm no expert either but I would assume the grey is neutral and the brown/black earth? Any way of tracing it back to the power cord to see which pin it's using?

    I would probably try connecting to neutral. I don't think anything would blow up trying either connection here given the hot wire is already connected up correctly.
    Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
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    • aarond
      aarond commented
      Editing a comment
      The grey wire comes from the transformer and goes nowhere after the bus. In any case, I've discovered Wolf's input is correct. I'll update with a detailed reply when I get back to my laptop.

  • #3
    A lot of the time, transformers have dual primaries to facilitate using 120V or 240V mains. I've seen the brown wire and paired combo before, and since they are connected together, my guess is the BRN/BLK is the other mains connection. The grey wire can be a Static shield wire, and I've seen this in grey before as well.
    Wolf
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    • #4
      Originally posted by Wolf View Post
      A lot of the time, transformers have dual primaries to facilitate using 120V or 240V mains. I've seen the brown wire and paired combo before, and since they are connected together, my guess is the BRN/BLK is the other mains connection. The grey wire can be a Static shield wire, and I've seen this in grey before as well.
      Wolf
      Thanks Wolf.

      After not getting much feedback here for a day or two I thought to seek out some electronics repair groups on Facebook. FB groups can be pretty hit or miss, I found one stinker and one good one that pretty much confirmed what you stated re 120/240V primaries. When I went to connect the loose wire to the bus the spade connector went on with zero friction. After adjusting the connector I powered the amp up with a variac and verified that DC offset was reasonable on all channels. It's been cold in my garage but the amp has worked fine for the couple of days that I have been out there since.

      I'd still like to figure out how to bridge this thing but in the meantime it's a huge upgrade from the underpowered amp I had in there previously. Next upgrade is speakers, likely Klipsch KL-650-THX clones built with buyout parts that I bought forever ago.
      Thanks,
      Aaron

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