Need some help with Princeton Reverb Build

Discussion in 'Amp Tech Center' started by KBarW, Feb 24, 2020.

  1. KBarW

    KBarW Tele-Meister

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    I'm back for a little advice. I've played a couple of shows with the Princeton and I have one coming up tomorrow so I pulled it out and played some Tele through it.

    There seems to be a problem......on notes on the high E string from the 5th fret up, there is a kind'a buzzing sound, or maybe better put - almost a doubling effect. I tried a different Tele with the same issue. Ran the main Tele through another amp and there's no problem with the guitar. I've also noticed that if I strum a chord and let it ring - it sounds like the Tremolo is on - but it isn't. Switch is off and the knobs are all the way down.

    Plugged another speaker into it - same problem.....so, it's not that. It just seems to not have much oomph once you get to the high E string (yes, I tried another Tele to rule out the guitar) and the weaker it gets, the more of the problem. The lower strings aren't having a problem......so, it seems to be some kind of higher frequency issue.

    Any ideas on what might be causing this high frequency motor-boating sound?

    Thanks....
     
  2. dan40

    dan40 Friend of Leo's

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    I wasn't able to read through the entire thread so I'm not sure if you have checked this already but in many new builds, the wires leading from the OT to each of the 6v6 sockets may need to be swapped. In some cases, the nfb loop can inject positive feedback into the circuit causing all kinds of strange issues. In most cases, a loud squeal will be heard when the amp is powered up but in other cases, the amp simply acts a bit strange. Swapping the two wires at the socket will cure the problem if this is what's causing it.
     
  3. KBarW

    KBarW Tele-Meister

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    Thanks.

    Are you saying that people accidently wire it wrong or that it just may need to be switched even if it was wired as per the directions?

    I did install a three-way negative feedback switch as outlined on Robinette's site. Was looking for the cleanest sound at higher volume that I could get.

    I guess I could try the other two settings to see if that has any effect at all.
     
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Yes, following the directions may still have it wired wrong. One of the shock brothers says this follows the 50/50/90 rule. There is a fifty fifty chance of wiring it right and it is wired wrong ninety percent of the time. Since you have a NFB switch, it would be easiest to switch the wires from the Output Transformer that attach to pin3 of the 6V6 sockets. Usually the wires are brown and blue. If dan40 is wrong with this diagnosis, the amp has a chance to squeal loudly when it is switched *on* so be prepared for that.

    The other two settings on the NFB switch should not matter with this.
     
  5. KBarW

    KBarW Tele-Meister

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    Based on the idea that, if wired wrong the amp will squeal, I'm sure it's wired correctly. I've used the amp for a couple of shows and it was great.

    I went out and played it some more yesterday afternoon and the problem with the high frequency stuff on the E string was gone. I wonder if it is only happening when it gets good and warm. However, the tremolo effect is still there when strumming a chord and letting it ring.

    I'm going to try and use it tonight, but I'll be taking along a spare amp just in case.
     
  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    dan40 and I are not so sure. Positive feedback issues can present in unexpected ways.

    It is still possible a tube could be causing the odd behavior. Maybe an ultrasonic oscillation.
     
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