Advice please: I have an opportunity to get a 1955 Princeton 5D2 narrow panel

Discussion in 'Glowing Bottle Tube Amp Forum' started by medoc, Feb 11, 2019.

  1. medoc

    medoc TDPRI Member

    Age:
    39
    4
    Jan 17, 2018
    Louisiana - New Orleans
    I've been in the market for 5F1 champ but I can get a really clean 5D2 right now; it's in excellent original condition and sounds great; It looks like most 5D2s were wide panel even in 1955 so this narrow panel 5D2 was likely a transitional amp? I suspect that this is actually a 5E2 and they were still using the 5D2 tube charts. How can I verify?

    In doing some research on the circuit, I found this quote at carlscustomamps.com and was hoping I could get some perspective from this board. What does he mean by flawed power section?

    "Wide Panel 5D2 1955
    This was the first Princeton to use the 12AX7 rather than the 6SL7 or 6SC7 of previous models. Fender went back to a grid leak biased first gain stage giving the amp a gritty sound. This is rare one.

    Again the power section is flawed in these amps and uses a similar configuration as the octal models. Increasing the filtering and some other slight changes can great reduce hum and increase punch. Adding a 3 prong grounded cord is a necessity. I also recommend adding 2 watt 1K screen resistor and replacing filter caps over 10 years old for the best sound.

    I've also tried this circuit a but found I prefer the cathode bias of the 5F2A later tweeds in a 12AX7 pre-amp.

    Narrow Panel 5E2 and 5F2 1955-56
    These rare versions were made with a cathode biased first gain stage. They also introduced negative feedback which gave them a smoother more even sound. Both used a choke transformer in the power section with rather minimal filtering. So additional filtering is helpful here to give amp punch and reduce hum. Adding a 3 prong grounded cord is a necessity. I also recommend adding 2 watt 1K screen resistor and replacing filter caps over 10 years old for the best sound."

    Has anyone actually seen a narrow panel 5D2? or were they likely 5E2?

    Thanks all!
     
    Last edited: Feb 11, 2019
  2. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Welcome on board! I don't think Carl is trying to be mysterious. "Again the power section was flawed" refers back to his earlier note on the 5B2, and both notes tell you what flaws he's talking about. "The power section is flawed in these amps. Increasing the filtering and some other slight changes can greatly reduce hum and increase punch. Adding a 3 prong grounded cord is a necessity. I also recommend adding a 2 watt 1K screen resistor and replacing filter caps over 10 years old for the best sound." In other words, they were under-filtered, lacked screen resistors, and have filter caps that age (many amps do, but aged filter caps in an under-filtered circuit are double trouble.) BTW Carl's a good guy, and would likely answer your questions himself.

    As for these vs. the 5f2a, he also gets that about right IMHO. The older Princetons get some love, though, and maybe their fans will help us out here.
     
    dan40 likes this.
  3. medoc

    medoc TDPRI Member

    Age:
    39
    4
    Jan 17, 2018
    Louisiana - New Orleans
    Good stuff; really appreciate it.
     
  4. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Medoc...welcome! If one had the amp with the back panel off so that one could see, then one could detect the particulars of input preamp stage. The 5D2 has a grid leak bias in that stage whereas the 5E2 has a cathode bypass circuit. If you go here....
    https://schematicheaven.net/fenderamps/princeton_5e2_schem.pdf

    And look at the right side of the layout, you will see a 25mfd cap paralleled with a 1.5k resistor. This is the cathode bypass circuit. The 5D2 does not these two components in that position. That would be the quickest clue as to what circuit is there.
     
    King Fan likes this.
  5. medoc

    medoc TDPRI Member

    Age:
    39
    4
    Jan 17, 2018
    Louisiana - New Orleans
    Great info. Thanks. Is the cathode bias/5E2 preferable??
     
  6. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Medoc, just a heads up.... generally, when we say cathode biased, we are talking about the output stage.
    It is true that that cathode bypass circuit is cathode biasing for that preamp triode versus the grid leak biasing that is seen in the 5D2 input preamp stage.
    To your your question, better might be subjective as some folks may prefer one over the other. Grid leak biasing can have issues when a player wants to use boost/overdrive pedals in front of the amp. Fender did not build any grid leak biased amps that come to my memory after the 1955 circuits were introduced.....the ‘E’ in the 5E2 indicates 1955.
    The market holds the 1955 later Tweeds to higher values compared to the earlier Tweeds. That doesn’t mean that everyone has to agree that the sonics follow the market, right?
     
    medoc likes this.
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