Princeton Reverb Clone - another clone thread

[owen]

Built a PR for a friend. Chassis is done! sounds lovely.

Mods: switchable midrange tone pot; 3 way NFB; reverb dwell control; log taper reverb pot; 12” speaker (friend’s request); and obviously, slower tremolo.

Answered questions:
1) sourcing Princeton Reverb chassis with non-angled/flat front: ordered one from zachmdhunter on ebay.

[Latole]

Google fender princeton reverb chassis

https://www.mojotone.com/Blackface-Princeton-Reverb-AA1164-Style-Chassis

[Latole]

https://www.tubeampdoctor.com/en/amp-chassis-for-blackface-princeton-rev.-style-aa1164

[Latole]

https://modulusamplification.com/Blackface-Princeton-Reverb-Chassis-Faceplates-with-Logo-P5266373.aspx

[sluckey]

Google fender princeton reverb chassis

None of those chassis have a ***FLAT*** front. All are angled.

[Latole]

Google fender princeton reverb chassis

None of those chassis have a ***FLAT*** front. All are angled.

I see they are flat !!

This is an angle chassis or what is it ?

[sluckey]

Google fender princeton reverb chassis

None of those chassis have a ***FLAT*** front. All are angled.

I see they are flat !!

Those pics are deceiving. Look at the video on the modulus link you provided.

[Latole]

Modulus chassis in video and what they show in my picture are not the same chassis !! WTF

[sluckey]

Modulus chassis in video and what they show in my picture are not the same chassis !! WTF

They are the same. Look at that odd PT cutout.

[Latole]

Modulus chassis in video and what they show in my picture are not the same chassis !! WTF

They are the same. Look at that odd PT cutout.

Thanks but I give up.

[Latole]

owen ,

Why do you want a flat front ?

[ac427v]

google                                  square angled blackface princeton chassis        will find you zachmdhunter site on ebay. I have bought from him with good results.  Sorry, I can't figure how to paste the link.

[sluckey]

https://www.ebay.com/itm/324949876865?hash=item4ba885a081:g:-20AAOSwaylhv2hE

[dwinstonwood]

I have bought from him with good results.

Same here. I've purchased three chassis from him. Excellent quality and free shipping.

Here's the square angled PR chassis:
https://www.ebay.com/itm/324949876865?hash=item4ba885a081:g:-20AAOSwaylhv2hE

Edit: sluckey, we posted at the same time.

[Latole]

Good job!  E-Bay, what else ?

[owen]

I found zach’s flat front one this morning. for some reason I only saw his blank one with no cutouts before.

this is my sixth chassis from him, haha. many thanks for the help. just ordered one.

[owen]

owen ,

Why do you want a flat front ?

purely aesthetics. I designed a new cabinet and a friend wants a flat-front princeton reverb in that cabinet. slightly more matchless look than fender.

[Latole]

owen ,

Why do you want a flat front ?

purely aesthetics. I designed a new cabinet and a friend wants a flat-front princeton reverb in that cabinet. slightly more matchless look than fender.

Thanks for your answer, this style of cabinet is also a great idea

[owen]

Amp is ‘finished’. Might swap a couple values when I choose a speaker. It worked first time on fire up. all voltages spot on. Biased 62% for that sweet, sweet tremolo, LOW noise floor, but a little hiss at max treble (can’t be from the TWO carbon comps…)

Time to build the cabinet.

I'm not sure I find use in the dwell control beyond a very specific value. at stock 1m it is just way too cavernous, but around 7 to 8 on a pot, it's perfect. I'll measure the pot and substitute the proper resistor, or a trimpot on the board to keep lead lengths tidy.

this is my 4th Princeton variant I've built including brown Princeton and tweed harvard. love these things.

[owen]

found a slight concern: I have to ‘jump start’ the tremolo.

if i power on the amp, turn the tremolo intensity to ‘10’ with speed at ‘1’ there is no tremolo. if i turn the speed knob up a minuscule amount, the tremolo will slowly ramp up and start pulsing. if i turn the speed back down to ‘1’ or the  lowest setting, tremolo is still there just pulsing at the slowest speed as it should.

i’ve rechecked all grounds, and connections. i did modify the tremolo with two .02 caps for
slower speed.

the bias current is at 22.3mA for one 6v6, 21ma for the second, plate voltage is at 411 volts (using a lower b+ power transformer.

the only other issue is once tremolo intensity is at 75% of max, there’s a scratchiness to the pot (for example between ‘7’ and ‘8’) have checked for DC and swapped pots to no avail.

i’ll do a full chart of measurements this weekend, but these two symptoms seemed related.

[sluckey]

found a slight concern: I have to ‘jump start’ the tremolo.

if i power on the amp, turn the tremolo intensity to ‘10’ with speed at ‘1’ there is no tremolo. if i turn the speed knob up a minuscule amount, the tremolo will slowly ramp up and start pulsing. if i turn the speed back down to ‘1’ or the  lowest setting, tremolo is still there just pulsing at the slowest speed as it should.

the only other issue is once tremolo intensity is at 75% of max, there’s a scratchiness to the pot (for example between ‘7’ and ‘8’) have checked for DC and swapped pots to no avail.

It's pretty common for the tremolo oscillator to drop out on the slow speed. A stronger 12AX7 would probably fix this issue, but I'd replace the oscillator cathode resistor/cap with a 5mm red LED (cathode to ground). The LED will boost the amplitude of the trem signal and allow the oscillator to operate reliably over the entire speed range.

I've never seen the scratchy INT pot issue. Disable the trem with the footswitch or a gator clip lead between the FS jack and chassis. Still scratchy? Monitor the bias voltage on pin 5 of the output tubes. Is it affected by the scratchy pot?

[owen]

It's pretty common for the tremolo oscillator to drop out on the slow speed. A stronger 12AX7 would probably fix this issue, but I'd replace the oscillator cathode resistor/cap with a 5mm red LED (cathode to ground). The LED will boost the amplitude of the trem signal and allow the oscillator to operate reliably over the entire speed range.

I've never seen the scratchy INT pot issue. Disable the trem with the footswitch or a gator clip lead between the FS jack and chassis. Still scratchy? Monitor the bias voltage on pin 5 of the output tubes. Is it affected by the scratchy pot?

I will try the LED. I don’t have any red, (just every other water clear color of the spectrum.)

and I wonder if my footswitch jack (trs) is causing that pot issue. Will do these later this evening and report back.

[sluckey]

Different colors have different voltage drops. Red and yellow work the best of all the colors I tried.