New silver face Princeton non reverb w/questions.

Discussion in 'Amp Central Station' started by mixtery, Oct 17, 2020 at 11:13 AM.

  1. mixtery

    mixtery TDPRI Member

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    I just picked up this '75 Princeton non reverb and it looks to have a '69 speaker in it that I assume is reconed. It sounds amazing so clean and full all the way up the dial. Some speaker flub if it's on 10 or hit with loud overdrive pedal. I am not getting any tremolo at all and I have read it's likely a bad 7025tube (they are new JJ ecc83s), over bias, or one of the .01 uf disc shaped caps in the middle of the board. Mine has 2 x .01 uf caps and one of them looks a little melted, perhaps by a soldering iron. Should there be 3 of these caps or only two in the non reverb model?
    Thanks to all here this forum has really such great info!

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  2. Wildeman

    Wildeman Tele-Meister

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    Sorry if im stating the obvious, do you need a footswitch for the trem? My Twin wont trem without one. And, yes that cap looks damaged, might be the culprit.
     
  3. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Your amp does have 3 caps, one is just not a disc cap. (I see a typical '70's "blue blob" cap there) The Princeton Trem is always on unless you have a switch connected.
    That cap may be bad or may not, it's just hard to say. You can temporarily just solder one in parallel to it to see. The worst that will do is slow down the tremelo range.
    It is just as likely the bias thing though.

    Also, check the impedance (just in case) on that non original alnico speaker, it looks a lot like some Fender PA/amp speakers that were 16 ohm.
     
  4. milocj

    milocj Friend of Leo's

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    Make sure to clean the footswitch jack if you haven't tried plugging a switch in and out yet. These RCA jacks can build up just enough corrosion to short the jack out and effectively turn the tremolo off without looking crusty or being mistreated.
     
  5. mixtery

    mixtery TDPRI Member

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    I will spray some caig's pro gold on an RCA jack and try that as an easy fix but I'm guessing it's the bias as well. I'll try the parallel cap trick in the disc caps.
    These "blue blob" caps are from the 70's? But non original right?

    I just measured the speaker and it's 7.5 ohms so hopefully the real alnico deal.
     
  6. keithb7

    keithb7 Friend of Leo's

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    Find an old RCA wire. Maybe an older TV video or sound cable. I think they can still be had at the dollar store for cheap. Cut 1 male RCA connection off the end. Leave a little bit of wire. Remove the outer shield wire covering off of both wires going into the RCA plug end. Once trimmed off, twist the 2 bare exposed copper wires together. Wrap it in tape if you like. Insert it into the RCA female jack on the back of your amp chassis. Now your trem works without a foot switch.
     
  7. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Blue blobs are probably original, I think they're pretty good myself. Not that it's a big thing either way!
    There should be a 1 meg resistor for the tremelo just below those caps in your pic. If it's too far out of spec the trem may not work. Sometimes I replace it with about a 470k resistor for stronger tremelo.
     
  8. Paul G.

    Paul G. Friend of Leo's

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    Princeton does not need a jumper to work, jumper shuts the trem off.

    Before you go soldering, yanking and whatnot, check your amps bias. Princeton trem is bias vary and if the amp is biased too hot, your trem will be very weak. If the bias is ok, I'd check the three oscillator caps.
     
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  9. BobbyZ

    BobbyZ Doctor of Teleocity

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    Before you do anything change those white Mallory electrolytic caps in the amp. At least do the one in the trem circuit, that might be the problem. I'd just do all the electrolytic caps, because the filter caps in the can and the Mallory in the bias supply can burn the power transformer. The small ones on the board won't hurt anything but can be noisy and cause issues, like trem or reverb. (reverb isnot an issue here)
    If you haven't already pull the fuse and check the amp rating against what it say by the fuse holder.
    As stated you don't need a pedal or shorting jack on Princetons or Vibro Champs to turn on trem. That ain't the problem. Bias can be an issue on these.
    My 2 cents. That amp needs to get serviced, I'd put in a trim pot to set bias at the same time. After a basic service, with all new electrolytic caps, if the trem still doesn't work then you start to look at the "prime suspects" in that circuit.
    Honestly can't recall the last time I changed anything in a trem circuit in a Fender of this vintage.
     
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  10. mixtery

    mixtery TDPRI Member

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    Thank you I was thinking the Mallory caps looked older. Should I replace this main Cap as well?

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  11. Wildeman

    Wildeman Tele-Meister

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    I'm not of the opinion that all caps in old amps need to be replaced but big power caps like that definitely need to after 40 years. Some of those multi cans are unavailable so guys will disconnect it and put individual caps inside the amp so you can retain the look.
     
  12. BobbyZ

    BobbyZ Doctor of Teleocity

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    You can get a C&E cap can from Antique Electric Supply. It fits in just like that original old Mallory. Not a fan of individual caps if a suitable replacement is available and they are for Fenders. What scares a lot of guys is soldering them in. If you don't have a huge iron it is truly an exercise in frustration! I found an old 200 watt iron in an antique shop that made chanting cap cans FUN. It had a big chisel tip that didn't cool down when it hit the chassis. The solder melted almost instantly! Seriously the cap change took seconds with that thing.
    Use a small one and you'll wind up holding it in the chassis for ever, and heat up the chassis and probably melt rubber grommets in the process. A big iron with a big tip gets it done fast, the heat is off before it spreads. Only way to do it right.
    The filter and bias caps are the "critical" ones, cathode bypass caps won't hurt anything if they fail. However I've never had any luck with those and just replace them. In my experience the white Mallory caps are just plain junk. The later blackface small bypass caps are junk too. Only good bypass caps you might see are pre about 1965, the big toilet paper roll jobs, Mallory or maybe Astron. But they're over 50 years old now too.
    Electrolytic caps are like car batteries, time is not on their side. They supposedly last longer with frequent use and go bad if unused. With a Princeton or Champ you can bet they sat unused a lot too! Nobody wanted those amps until fairly recently, they sat in closets and under beds for years. That's why the old caps look so good in them, they aren't good, lack of use just kept the insides inside.
    Conversely take a Twin Reverb that's been used a lot and you'll see leaky, bulging caps in the dog house almost all the time. Amp still seems fine because nobody turns up a TR anymore.
     
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