Just got an unmodded '73 or '74 Princeton non-reverb combo amp. Anyone have experience with one of these? Mods? Can't find a complete schematic for non reverb silverface model. Has vibrato, would love to use the extra vibrato stage without vibrato.
I don't recall reading that Jerry disconnected the trem stage. I'll have to check Waldo's age and see. In any event, I've put a pull pot on the intensity of the trem on a few bigger fenders and it is an effective and simple way to increase gain (and volume). On the princeton, you can turn intensity all the way down... simpler and sometimes more effective method would be to use a shorted rca jack in the footswitch slot. By default on that amp the trem is on. The shorting jack will turn it off. Not the same as removing it though.search4sound wrote: I read somewhere that one reason why tremolo (aka vibrato) is removed from Twin Reverb and other amps with similar trem circuit is that this circuit can load down the circuit creating suboptimal tone. Any truth to this?
In the case of Jerry's TR mods, I assumed the reason for removing the trem was to free up the tube to be used for an extra stage. Maybe it was both? Related to this, I wonder if anyone has the vibrato mod and has A/B'd the normal channel (stock) and the vibrato channel (extra stage, no vibrato). How do they compare?
In the case of the Princeton, I read that the way the trem is connected does not load down the circuit. So I presume that I can turn down the intensity to 0 and the vibrato should sound the same as the normal channel?
+1 on the tonestack mod. I'll do the cathode bypass caps on the triode stages as well. I suppose I should consider replacing all the electrolytic caps, that amp is almost 40 years old.
Thanks for you recommendation not to upgrade the speaker to 12" or increase the gain - I've long wanted a push pull amp that sounds good at lower volumes. So do you still get shimmering Garcia clean with a 10" speaker?
What about preamp tapping the Princeton? Anything keeping me from doing that? Is it done the same way as with a TR?
search4sound wrote:Yes, Waldo's site shows how when the TR is used as a preamp with McIntosh for amp, the vibrato channel is used but the vibrato itself is removed from the circuit.
I'm not sure if this frees up the vibrato triode to be used as an extra gain stage, or if it is completely out of the circuit and the exctra stage I've heard referred to is actually the triode associated with the reverb that gets used in the vibrato channel. Now would thet be a 12AX7 or a 12AT7? And does the dry signal before the reverb get amplified before the signal splits off to the reverb, or does the signal split off and then only the reverb signal is amplified before being mixed back into the dry signal?