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Post subject: 1979 fender princeton export
Posted: Tue Apr 26, 2011 6:45 am
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hi new to the forum here and have a question.just bought the above amp a few weeks ago and its behaving funny.when i bought it from the guy he said it had no footswitch but the tremolo worked,i looked up the circuit diagram before i left and saw that the fs was just an open circuit with an rca socket.i brought a rca lead and a piece of copper to short it out.it did not seem to work so the guy knocked money off,when i got home and played around a bit with other foot switch's and swapping tubes i realized it was working but very very weak,now its on all the time without footswitch and the only way to turn it off is plugging in a shorted out rca lead.......anyone any idea's.thanks.


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 8:19 am
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All AA1164-based Princetons use the bias-modulated tremolo and the circuit is designed to be "on" without need for a footswitch. The only way to turn it off is with the footswitch. Thus, the amp is in fact operating correctly. The weak trem is itself likely the result of a tube issue.

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Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 8:32 am
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thanks for the reply.i was working off the aa964 non reverb schematics.


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 8:35 am
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Same deal -- the trem is always on.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 8:48 am
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thanks arjay.i dont understand the diagram then.looks like the pedal is an open circuit that closes when you engage the switch.


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 10:03 am
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The footswitch, when engaged, disables the half of the 12AX7 that acts as the oscillator by grounding the grid. When the footswitch is open (or unplugged), the trem tube remains integral to the circuit.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: 1979 fender princeton export
Posted: Tue Apr 26, 2011 10:24 am
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thanks for that.i am reading that reducing the 1m resister makes an improvement to the overall effect.anybody any experience with the weakness.cheers.


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