PRRI OT wiring question

Discussion in 'Amp Tech Center' started by toomanymods, Dec 29, 2020.

Tags:
  1. toomanymods

    toomanymods TDPRI Member

    Age:
    44
    Posts:
    14
    Joined:
    Dec 29, 2020
    Location:
    USA
    Hi all,


    I have a Princeton Reverb RI that I've messed with quite a bit (re-covered, 12" baffle, OT upgrade). One of the things I did was change the OT for a Hammond P-1760H (https://www.hammfg.com/files/parts/pdf/1760H.pdf). It's got 4/8/16 ohm outs. Basically doing the DR OT mod, with the added bonus of multiple impedance options. The 8ohm tap works great and I quite like the tone change.

    When I use the 4 ohm tap with 2 8 ohm speakers (i.e. the internal speaker and an 8 ohm cab) it is super quiet and distorted. Did I wire this incorrectly?

    wiring.jpg

    IMG_8752.jpg
     
  2. dogmeat

    dogmeat Friend of Leo's

    Age:
    70
    Posts:
    2,882
    Joined:
    Oct 12, 2017
    Location:
    Alaska
    looks right to me. to be clear, you are removing the jack cord of the on board speaker from the 8 ohm socket and putting it in one of the 4 ohm sockets. and you are adding a 2nd 8 ohm speaker plugged into the other 4 ohm socket. that should work. did you ohm the speakers? I don't think the polarity of the 2nd speaker matters but I would check that too
     
  3. toomanymods

    toomanymods TDPRI Member

    Age:
    44
    Posts:
    14
    Joined:
    Dec 29, 2020
    Location:
    USA
    That’s correct - I disconnect one 8 ohm speaker wire and plug both into the combined 4 ohm jacks. Both speakers are 8 ohms.

    I’ll check the polarity of the speakers next.
     
  4. milocj

    milocj Friend of Leo's Ad Free Member

    Posts:
    3,810
    Joined:
    Aug 21, 2005
    Location:
    Michigan
    If the PRRI is like the original version the internal jack has a switch on the contacts so you won't damage the transformer if you run it without a speaker/load. Using just the external speaker jack will have very low output.

    Did you leave the internal jack wired as it was with the switching contact in place? Moving the internal speaker over and using it with your two 4 ohm jacks would leave that insternal speaker jack shorted out.
     
    toomanymods and Junior Little like this.
  5. Junior Little

    Junior Little Tele-Meister

    Posts:
    303
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    The original 8 ohm jack isn't a switched jack, is it?
    [email protected] beat me to it!
     
    toomanymods likes this.
  6. toomanymods

    toomanymods TDPRI Member

    Age:
    44
    Posts:
    14
    Joined:
    Dec 29, 2020
    Location:
    USA
    Thanks guys!

    So if I replace the internal speaker jack it should work? Could I also just remove the 3rd switched lug?
     
  7. Junior Little

    Junior Little Tele-Meister

    Posts:
    303
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    The switch will stay grounded if no jack is inserted. I'd swap out the switched jack for a non-switched one. Should be good to go then. Use all non-switched jacks, but make sure you have at least one speaker plugged in.
     
    toomanymods likes this.
  8. toomanymods

    toomanymods TDPRI Member

    Age:
    44
    Posts:
    14
    Joined:
    Dec 29, 2020
    Location:
    USA
    Just finished the jack swap and it's working perfectly now. Thanks for the info, this was vexing me for a few days!
     
    Junior Little likes this.
  9. milocj

    milocj Friend of Leo's Ad Free Member

    Posts:
    3,810
    Joined:
    Aug 21, 2005
    Location:
    Michigan
    Glad to hear it.
     
  10. Junior Little

    Junior Little Tele-Meister

    Posts:
    303
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    Nice!
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.