Packard Bell Console Preamp? 12AU7 Micro Build Potential?

Discussion in 'Shock Brother's DIY Amps' started by Fixcinater, May 15, 2021.

  1. Fixcinater

    Fixcinater TDPRI Member

    Posts:
    54
    Joined:
    Mar 29, 2021
    Location:
    San Diego, USA
    Fresh pickup from Offer-Up, seller said it came out of a Packard Bell console. I saw it had blue molded caps and thought plus the tubes and chassis might be worth the $40 even if the transformers are shot.

    Tube compliment (at least what is installed and written on chassis in marker):
    12AU7A
    7025
    6U8A
    6AN8A
    6X4

    Seems like most of P-B's consoles were stereo integrated all on one chassis.

    PA-20 is stamped on one side of the chassis, power transformer and OT (I'm guessing it's sort of a pre-amp out?) are 394 (Foster), blue molded caps labeled Packard-Bell which apparently are similar or same as what came in 60s Fenders and should sound quite good still?


    I've built and enjoy a 5F1 in a 1x12 combo so I'd like this to somehow compliment that (ie, not a tweed micro Bassman) but maybe the small bottle power amp would be enough of a change. I also have a 2xEL84 Stromberg-Carlson and a 2x6V6 Victor PA amp I have been storing for later (when I have more experience and know what I want them to be).


    Planned 1st steps:

    Test PT as much as I can in place, figure out what the "OT" is
    Replace 2-prong AC cord
    Install fuse/power switch/lamp
    Replace filter caps (re-stuff cap can to save chassis room?)
    Replace damaged resistors on one tube

    Then plug in (light bulb limiter) and follow Robrob's start up procedure.

    Picts (from seller):

    43f4271925d54af8bb8dabfee0e7e78f.jpg 15fcabac27a84c7296c1bee30743b109.jpg
    f14db25b2aaa476ab51e84dce9bba4d5.jpg 803af1b3857b4587bfd415d91fc66bed.jpg
    ec4f3c0c026841cba048b898a0b37141.jpg 110011ca8e334049b474326de8ced323.jpg
    afc7b58bd9c14d799686505c0a5fa61f.jpg 4284a70058c64c468b8b0ee1c9135486.jpg
    02d8775b3dbb41b8800ba7692ef0596f.jpg 1e86ebd923604eb39ce4ef4d75792b32.jpg
     
    RollingBender likes this.
  2. printer2

    printer2 Poster Extraordinaire

    Posts:
    7,393
    Joined:
    May 24, 2010
    Location:
    Canada
    Fixcinater likes this.
  3. Fixcinater

    Fixcinater TDPRI Member

    Posts:
    54
    Joined:
    Mar 29, 2021
    Location:
    San Diego, USA
  4. printer2

    printer2 Poster Extraordinaire

    Posts:
    7,393
    Joined:
    May 24, 2010
    Location:
    Canada
    I would think you have an idea what you want and while it might be interesting to know what other people think about design and see what they did, but that is just a geeky thing. Actually not too hard to do with the tube pinout and just trace through the grids and plates, don't need to know the component values, sort of a block diagram of what you got (that would be me). I am thinking the 6U8A and the 6AN8A triodes (being a pentode-triode tube) would be used as the output tube (rather than a 12AU7). Mind you they could have triode strapped the pentodes also, really they could have done all kinds of different stuff. I am not going to even look on the underside of the chassis, I need to work on a guitar.

    Might want to look at the Traynor Dark Horse schematic, they put a 12AU7 through an output transformer that runs EL84's to give it a 2W option.
     
    Fixcinater likes this.
  5. mrriggs

    mrriggs Tele-Meister

    Age:
    41
    Posts:
    194
    Joined:
    May 24, 2020
    Location:
    Vancouver, WA
    It looks like someone robbed the EL84s and jabbed two random tubes into the sockets so it wouldn't look like it was missing anything. The sockets are still wired for a pair of power tubes.
     
    Fixcinater likes this.
  6. Nickfl

    Nickfl Friend of Leo's

    Posts:
    2,588
    Joined:
    May 24, 2016
    Location:
    Florida
    I'd gut it and test the transformers, then go from there once you know if they are viable.
     
    Fixcinater likes this.
  7. Fixcinater

    Fixcinater TDPRI Member

    Posts:
    54
    Joined:
    Mar 29, 2021
    Location:
    San Diego, USA
    That's exactly what happened, plus a power supply resistor breaking a lead and looking toasted. There is also some damage to the "Stereo" jack nearby, so may have just been broken mechanically.
     
  8. Fixcinater

    Fixcinater TDPRI Member

    Posts:
    54
    Joined:
    Mar 29, 2021
    Location:
    San Diego, USA
    Thanks for your thoughts and write-up. Turns out it's all stock wiring, just with a power supply resistor that is smoked. So next step is check out the transformers and go from there. Will report back once I've taken some voltages and checked ratios on the OT.

    Thanks again!
     
    Nickfl likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.