1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Princeton Reverb Wiring Question

Discussion in 'Amp Tech Center' started by Forthefunofit, Oct 30, 2020.

  1. Forthefunofit

    Forthefunofit TDPRI Member

    Posts:
    5
    Joined:
    Oct 30, 2020
    Location:
    Minnesota
    Hi all!
    I'm in the process of hand building my first amp, a modified PR clone, and have run into a possible issue that I'd appreciate some expert help with.
    I've been using StewMacs instructions just as a chassis wiring reference and have hit a discrepancy (I think) in the B+3 & B+4 wiring compared to Fender's schematic. S-M has the jumper connecting the plate load resistors skipping past the 56k phase inverter resistor, & then a separate jumper from that 56k resistor going to the B+3 connection at the eyelet where the can cap B+3 connects to the 18k resistor. This looks like it would put 320v at the PI plate load resistor instead of 240v as Fender's schematic shows.
    Am I not seeing this correctly, or is it an error in StewMac's instructions?
    Any help would be greatly appreciated!
    Thanks!
     
  2. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,184
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    A picture of the stew Mac schematic or even the layout would be of help as would the same for the Fender circuit.
     
  3. Wally

    Wally Telefied Ad Free Member

    Posts:
    37,184
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    And..welcome...
     
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,246
    Joined:
    Dec 30, 2019
    Location:
    california
    +1 ^^^^

    You have me looking cross eyed. SM has the eyelets numbered. If you would use the eyelet numbers, maybe that would help.
     
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,246
    Joined:
    Dec 30, 2019
    Location:
    california
    Yep, that is what I see. The plate resistor for the V4 pin6 is fed with a higher B+ (320V).

    Are you going to stay true to the Fender design or???
     
    Last edited: Oct 30, 2020
  6. Forthefunofit

    Forthefunofit TDPRI Member

    Posts:
    5
    Joined:
    Oct 30, 2020
    Location:
    Minnesota
    Sorry, I'm also new to forums, but I will get the hang of this.
     
  7. Forthefunofit

    Forthefunofit TDPRI Member

    Posts:
    5
    Joined:
    Oct 30, 2020
    Location:
    Minnesota
    I believe I am going to stay with Fender's design... unless there's a good reason to go with the higher voltage. Any thoughts on this?

    Funny thing is that StewMac's instructions (and physical layout diagram) calls for the higher voltage connection while the AA1164 schematic that they also include in the instruction book shows Fender's original lower voltage connection to the PI plate load resistor. That's what made me question their altered layout in the first place. Didn't know if it was intentional or a mistake.
     
  8. D'tar

    D'tar Friend of Leo's

    Posts:
    3,073
    Joined:
    Jan 11, 2013
    Location:
    WNY
  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,246
    Joined:
    Dec 30, 2019
    Location:
    california
    Just noticed D'tar mentioned the Stokes mod. If you want more clean perhaps you could go that way.
    Rob's site says of the Stokes mod: *This is one of the most "didn't like it so I reversed it" mods for the Princeton Reverb.*

    YMMV.
     
    SnidelyWhiplash likes this.
  10. Forthefunofit

    Forthefunofit TDPRI Member

    Posts:
    5
    Joined:
    Oct 30, 2020
    Location:
    Minnesota
    Thanks guys!
    I think I'm going to stick with the lower factory voltage as I don't ever plan to run 6L6's or 5881's, & the stock clean headroom is more than enough for my noddling around at home.
    I appreciate all the help!
     
    D'tar and Lowerleftcoast like this.
  11. Forthefunofit

    Forthefunofit TDPRI Member

    Posts:
    5
    Joined:
    Oct 30, 2020
    Location:
    Minnesota
    D'tar,
    Thanks for reminding me of this! I had read through Rob's site about 6-8 months ago when I was trying to decide on what mods to include in my build. The Stokes mod was one of the ones I had decided against.
     
    robrob and D'tar like this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.