Switch wiring for second series cabinet

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by bordonbert, Jan 19, 2015.

  1. bordonbert

    bordonbert Member

    Jan 19, 2015
    I have a H&K Tubemeister 36 which has an output impedance of 8-16ohm. This is from a single output socket without any need for output switching or Tx taps. It has a very over-engineered output stage, 4 x EL84s and an oversized output Tx to prodce 36W, to handle the mismatches involved.

    I have 2 x 112 cabs with a 8ohm Celestion Vintage 30 in each. I want to wire in the ability to drive either, one of them at 8ohm or the pair at 16ohm, hence series connection through a slave socket on the main cab.

    Does anyone have any experience with this setup? I'm sure it can be done reasonably with switching on the slave jack socket, but I am leaning towards adding a slider switch to the jack plate to handle the changeover.

    Yes, I am aware that a blowout in either speaker would unload the output stage which would be a "bad thing" for it. It won't like driving an open circuit but I'm pretty sure the H&K will handle it for a short period and, let's be honest, if your output suddenly cuts out you generally stop playing! No playing, no output valve/Tx signal current, no change to quiescent current, no problem.

    As an aside, has anyone ever come across a protection unit which senses the presence of both voltage and current at the speaker output of the amp and pulls in a load resistor when it sees voltage but no speaker current?
  2. J M Fahey

    J M Fahey Member

    May 22, 2009
    Not exactly but a protection exists, used by Peavey and others, which clamps excess output peaks .

    It does take a little bite out of overdriven sound though, that's why some don't like it.

    But as you already know, there's not such a thing as "free lunch".

    Personally, I install it in all my amps, in my book protecting the expensive OT is well worth it.

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