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Thread: Blackface Princeton Reverb problem ...

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    Blackface Princeton Reverb problem ...

    I am just starting to restore my Princeton reverb blackface amp. First of all I have the following problems: The heating voltage of the rectifier tube is 4 volts, the heating voltage of the other tubes is about 5.7 volts. The anode voltage after the rectifier tube is about 440 volts without load, but as soon as I plug in the power tubes it drops to about 300 volts, which is much too low. So it looks as if the transformer (original 110 volts with 220 volts transformer before) does not provide enough power. How can this be? The Cs seem to be ok. Transformers don't usually get worse with time, do they? .... What ideas do you have?

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    Forum Member phantomman's Avatar
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    Re: Blackface Princeton Reverb problem ...

    The low heater voltages (both 5V and 6.3V) and the reduced output voltage from the rectifier would seem to indicate a power-tranny issue. Is it the correct type for a Princeton Reverb? An original Fender will be stamped with the P/N 125P1B (FEIC) or 022772 (FMI).
    Last edited by phantomman; 01-23-2021 at 10:15 AM.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Blackface Princeton Reverb problem ...

    Quote Originally Posted by phantomman View Post
    The low heater voltages (both 5V and 6.3V) and the reduced output voltage from the rectifier would seem to indicate a power-tranny issue. Is it the correct type for a Princeton Reverb? An original Fender will be stamped with the P/N 125P1B (FEIC) or 022772 (FMI).
    Yes its stamped with the number 022772 ...

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    Forum Member phantomman's Avatar
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    Re: Blackface Princeton Reverb problem ...

    In that case I'd suspect that the tranny is tired -- a replacement may be in order. Another option would be to have the existing iron rewound to factory specs. Mercury Magnetics used to offer this service, they may still.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Blackface Princeton Reverb problem ...

    Thank you very much for helping ... Can a tranny age and become weaker? I didn't know that ...

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    Forum Member Don's Avatar
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    Re: Blackface Princeton Reverb problem ...

    What's your line voltage? I know it's higher than it used to be in the old days, but you could have an issue where it's much lower. I use a Variac and a Kill A Watt to make sure the voltage is where I want it when working on amps. If the dehumidifier, central air come on or my son is welding, the voltage can get pretty low.

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    Forum Member phantomman's Avatar
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    Re: Blackface Princeton Reverb problem ...

    Shorted windings within the core can reduce the available output voltage at the secondary taps. It's not a common phenomenon but it does occur periodically. If the amp is otherwise all original, I'd seriously consider having the P/T rewound rather than replacing it with a modern equivalent. My '65 Princeton Reverb is all original save for a replacement speaker, a Fender-marked CTS alnico from a Super Reverb. It also has a standby switch, a mod that is invisible and totally reversible.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Blackface Princeton Reverb problem ...

    Quote Originally Posted by Don View Post
    What's your line voltage? I know it's higher than it used to be in the old days, but you could have an issue where it's much lower. I use a Variac and a Kill A Watt to make sure the voltage is where I want it when working on amps. If the dehumidifier, central air come on or my son is welding, the voltage can get pretty low.
    we have 230 volts stable here in europe. i have a step down transformer that makes 110 volts out of it before the original fender tranny, the 110 volts also come out of the step down there.

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    Forum Member phantomman's Avatar
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    Re: Blackface Princeton Reverb problem ...

    Fender used an alternate power tranny for export models intended for Europe. It carries Fender P/N 020873. You might try locating one of these -- it would allow you to ditch the stand-alone step-down converter. They must rare though, I've never even seen one in my fifty years of working on Fender equipment.
    "When injustice becomes law then rebellion becomes duty."

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    Forum Member phantomman's Avatar
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    Re: Blackface Princeton Reverb problem ...

    After further consideration (and a third cup of coffee) I think you should check the output of that step-down converter. If it's flaking out that might account for the low voltages you've measured in the amp.
    "When injustice becomes law then rebellion becomes duty."

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    Forum Member Don's Avatar
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    Re: Blackface Princeton Reverb problem ...

    Quote Originally Posted by phantomman View Post
    After further consideration (and a third cup of coffee) I think you should check the output of that step-down converter. If it's flaking out that might account for the low voltages you've measured in the amp.
    We need a like button so I can say I agree.

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    Re: Blackface Princeton Reverb problem ...

    Quote Originally Posted by Don View Post
    We need a like button so I can say I agree.
    No, I checked. The voltage is stable 110V after the step up tranny

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    Re: Blackface Princeton Reverb problem ...

    If that be the case and you're certain then it's time to start digging into that power tranny.
    "When injustice becomes law then rebellion becomes duty."

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    Re: Blackface Princeton Reverb problem ...

    Quote Originally Posted by phantomman View Post
    If that be the case and you're certain then it's time to start digging into that power tranny.
    I will check again tomorrow... but thats what we measured today....

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