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Princeton Re-issue Reverb slight moan.

Discussion in 'Amp Tech Center' started by tecelaster, Feb 13, 2017.

  1. tecelaster

    tecelaster Tele-Meister

    499
    Apr 11, 2015
    Glasgow, Scotland
    Well....I've always noticed that there is hum when the reverb is high, so while I wait for a pair of new 6V6 output tubes it seems timely to see what I can do to cure the issue. First off, the stock RCA phono leads are cheap plastic crap, so I will replace with shielded cable and Switchcraft connectors. Taking the tank out and then de-bagging the spring unit it's obvious that the bag has no shielding layer either (do vintage amps have that?). I've put copper tape on cardboard and then covered the tank on top and bottom. Should help.
    I won't have time to solder up the new cables until next weekend, but fingers crossed that these small mods help.
    This Princeton wasn't exactly cheap, so I'm struggling to understand why Fender didn't try a bit harder to do the job just that little bit better for us 'Verb hogs.
     
  2. milocj

    milocj Friend of Leo's Ad Free Member

    Aug 21, 2005
    Michigan
    The originals didn't have a shielded tank. The bottom of it usually had a thick cardboard bottom attached to it and three long strips of foam rubber along the top to help dampen external vibrations.

    Bad shielding on the footswitch can also add to noise since it carries signal when using it. I haven't noticed noise issues with the newer foot switches, but the switches themselves aren't the greatest quality even though they are Carling. I've had to replace a couple of the switches.
     
  3. Platefire

    Platefire Friend of Leo's

    Age:
    69
    Nov 3, 2003
    North Louisiana around Many
    Did you try:

    1-a different known good driver tube and recovery tube?

    2-Try the reverb with the foot-switch UN-plugged.

    3-Do you have another fender type amp/tank to plug the cables from your amp into a different known good working tank.

    4-Clean existing rca plugs/jacks/switch with Deoxit?

    Platefire
     
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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    I like all of Platefire's suggestions above.

    The reverb driver tube is pushed pretty hard with high plate voltage so they tend to wear out quicker than the other tubes. A bad reverb driver or recovery tube can cause hum and other, sometimes weird issues.
     
  6. tecelaster

    tecelaster Tele-Meister

    499
    Apr 11, 2015
    Glasgow, Scotland
    Thanks for the replies folks.
    The hum from the reverb circuit doesn't make the amp unusable, but I'd like to try and lessen it. I have other spring reverb tanks but as studio effects not on amps.
    The switch connected or disconnected makes very little difference to the level of hum BTW.
    I've just finished re-biasing the amp for new 6V6's so my next step is to test whether the hum is bad shielding or not. I'll move the tank away from the chassis/cabinet and try some good quality shielded phono cables, test for ground continuity etc. - all these things first. If there's no improvement then I'll look at a new tube for the driver.
    Cheers.
     
  7. tecelaster

    tecelaster Tele-Meister

    499
    Apr 11, 2015
    Glasgow, Scotland
    Quick update - the extra shielding on the tank and a good clean of all the sockets and plugs has fixed the hum. Even with the reverb set full on there's nothing detectable.
    Sometimes the easiest fixes do work.
     
  8. jazzguitar

    jazzguitar Tele-Afflicted

    Mar 17, 2003
    Germany
    Interesting. All the vintage ones have a little extra hum with the reverb fully open. Even without the tank!
     
  9. tecelaster

    tecelaster Tele-Meister

    499
    Apr 11, 2015
    Glasgow, Scotland
    Yes - I'm also amazed at the change. With the reverb at 10 all you can hear is some low level hiss - which I'd expect. Maybe I've just got lucky, or vintage amps are over-rated! (joking). Mind you, hum is in the ear of the beholder.
     
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