Princeton AA964 clone low volume output and various other issues

[Bruce / Mission Amps]

You mean the riveted terminal part came off the carbon track? Weird, I've seen them loose but not come off...break off yes.
Was it a new one or a salvaged part?

[Les s of Paul]

Brand new Alpha pot, strange thing, to all appearances its a perfectly good pot, until you ohm it. one of the terminals was completly open air, or when you're lucky 1.5Mohm across the whole pot. i just have a knack for finding the broken ones in a batch, always broke in ways you would never expect.

On a side note, Denver, makes me wish i was back home around Pueblo, not here in the east... nothing but rain or clouds it seems... far as i'm concerned your lucky to get to live out there

[Les s of Paul]

Hmm, looks like one final problem has presented itself. should'nt be anything major, just hoping someone might know off the top of their head. anyways, i cannot connect the tremolo footswitch to ground without a large ammount of high pitched squeal emitting. it seems the intensity pot has a small effect on it. i had to redo a couple of grounds to clean things up a bit, all i can figure is the speed pot isnt grounded, or i soldered the wires back in the wrong spot.

[nickb]

Unplug the foot switch and short to ground as shown here:. Does the problem go away?

When not grounded does the tremolo work normally?
Does the speed pot work?

[Bruce / Mission Amps]

Brand new Alpha pot, strange thing, to all appearances its a perfectly good pot, until you ohm it. one of the terminals was completly open air, or when you're lucky 1.5Mohm across the whole pot. i just have a knack for finding the broken ones in a batch, always broke in ways you would never expect.

On a side note, Denver, makes me wish i was back home around Pueblo, not here in the east... nothing but rain or clouds it seems... far as i'm concerned your lucky to get to live out there

Cool. I played 3 1/2 hours at the annual
Chile & Frijoles Festival down in Pueblo, CO this September... with Dan Treanor (a Pueblo native) and the Afrosippi Band.
Dan Treanor - Home

[Les s of Paul]

With the ground disconnected i don't remember the tremolo at all, might not have had it cranked up enough. i will have to try the ground you show there. and its not quite a footswitch, i have a spdt center off for an on-off-footswitch selection. far as i remember, it worked before i touched up the grounds. i'll have an answer here shortly.

[Les s of Paul]

Well, it would seem Grounded or not, theres no tremolo i've heard its a very soft tremolo, but i can hear it at all. Whether its a bug of the amp, or just how the circuit works i dont know. but for some reason, that squealing problem vanished aswell. so, ground disconnected = tremolo, grounded = off? swung both speed and intensity pot through the full range, no change in either position

[nickb]

Yes, grounded is off. I'd like to see voltage measurements from around the tremolo with it turned off. Take at all points indicated
I recall from your earlier numbers that you saw the plate voltage vary when the tremolo was on. That's good, but what we don't know is if the signal is big enough and unless you have a scope it's going to be hard to figure out. Since we know the circuit works in other amps there has to a wiring or component problem.

[Les s of Paul]

All voltages with reference to ground as usual, most of the voltage ranges are fairly accurate, voltages should be with speed pot at near min and intensity maxed for ease of measuring. i think the meter has about a 1/6th to 1/10th second refresh rate.

[Jazz P Bass]

It would really help if you took some Vac readings. (right where you took the Vdc ones.)
The circuit is called a LFO (low frequency oscillator)
In the end it varies the bias voltage to the output tubes.
If the circuit surrounding the 12AX7 is not oscillating, then you will not have a Tremelo effect.
It is usually the caps that fail.

[nickb]

OK that looks good (except that you did the measurements with the tremolo on by the look of things). I really wanted it to be off so we could get stable readings. Anyway, since it's varying it's likely that's it's oscillating. Now we need to know how big the signals are. As I mentioned before you really need a scope to do this. Try checking the same points using your meter set to AC volts and the tremolo set to fastest (lowest resistance of speed pot).

[Les s of Paul]

Just thought i'd say "i'm not dead yet!"

been insanely busy lately, still haven't finished the tremolo problem, maybe i'll have that done soon, we'll see.
ill post back here once i have the voltages

[Les s of Paul]

Alright, finally replaced the volume pot, now the amp is finally alive no hums, just awesome tone. Anyways, the tremolo is still a problem, however i have a symptom that i had not observed previously because i wasn't actually grounding the tremolo (forgot the footswitch jack isnt a shorting type) anyways, when i ground the tremolo, a nasty fizzing noise comes through, its quite trebly and the speed pot seems to make the fizz a little louder and more trebly, the more its turned up. Also, only after grounding the tremolo for a period, turning the volume to zero resulted in an oscillating pop noise, only with the volume fully down. turn it up the slightest and the pop dissapears.
i can't get the voltages right now as my DMM needed calibration and had to be sent in... i had that fizz noise before but cant remember what i changed that fixed it.

Hopefully this helps, if not i'll get the voltages when my meter is back.

[Les s of Paul]

Alright, i now have voltages. speed pot was set to minimum resistance. which interestingly enough had a small effect on some hum from the amp.

oh, a couple other details that might help-hurt. On startup tremolo off, the amp makes 3-7 LOUD pops. also, with the trem grounded the amp has a high pitched radio noise type sound. when probing around the trem circuit, the noise goes away.

ALL voltages were taken without an input signal. if you need any other information i will provide that i can, and yes i can get ahold of an Ocilioscope, just confirmed today.

Sorry if the color scheme is a little whacky, i can re-write it if need be.