Customized Princeton Build: Mods suggestions?

[mirage_indigo]

I'm working on the initial layout for a BF Princeton Reverb. Being me, I've decided I can't just leave well enough alone, so I'll be trying my own layout (mostly since I already have a set of Hammond trannies in stock).
I'll be using a Hammond 270Fx and a 1620 for output.

What I'm after is which mods to people recommend for these style circuits?

So far, I'll be making the following changes:
- 25kB Mid control
- Pre PI, bootstrap style MV mod.
- SS rectified With Solen fast caps 47/27/27/27 laid out in chassis. 1M safety bleeder across supply.
- Hammond 125A reverb driver with push/pull style hookup using 12AT7.
- Single adjustment bias supply. bias probe points.
- Was considering a pentode/triode switch, but I used one of these in my last amp, and I basically never change it from pentode.

I'll probably stick with the 6v6 tubes. I'm debating DC heaters for the preamp tubes. I used a basic CLC filter in my Tweed/Delux mashup buid and it worked really well. I'm using a mojotone cusotm chassis , so 17" x 6.5" x 2.5".

Specifically, Dwell control? Passive Fx loop? Slower trem?

[xtian]

My opinions only: Mid boost pot is awesome, but master volume in a PR is basically useless. SS recto and heavy filtering is fine, as long as you don't push much past 350v plate-cathode.

[didit]

Hello -

Appears deviant largely from any reasoned Princeton template. More in the shape of a "Vibrato" channel HiFi Deluxe Reverb, presuming you'd sensibly want to include AB763 LTP PI. Or even a Vibrolux. Transformer sizing allows for 6L6 which is cool.

Similar project coming together here. Though somewhat smaller power transformer and awaiting prototype for decisions on output transformer options. Will be built on a stock Princeton Reverb steel chassis, with SS rectifier and "can" electrolytic caps from JJ - 32uF-32uF in a Pi filter with standard Fender choke and then 40uF-20uF-40uF using a 40/20/20/20. Reverb will be cap-coupled constant current transformerless using 6CX6 pentode, and will include back-panel dwell. No FX loop but will have a Dumble-esque FET. And yes, some tremolo tweaks to give slower and perhaps deeper effect.

Suggest it's all down to taste and desires. Be happy.

Best .. Ian

[Mark]

Have you seen the Valve Wizard mod?

http://www.valvewizard.co.uk/cathodyne.html

https://robrobinette.com/AA1164_Princeton_Reverb.htm

I'd use a bigger output transformer, even a Deluxe Reverb one.

[mirage_indigo]

I've been consulting Rob's excellent site a lot. Part of why I'm asking here is to help sort through all the options. The main mod suggestions seem to be around the cathodyne getting a much much bigger grid stopper input impedance either by fixed resistor or master input pot. That and everybody seems to love the mid pot addition.

I'd seen ValveWizard's site, but hadn't really groked he'd worked out a DC coupled cathodyne. That would makes sense since the cathodyne is a pair of cathode follower with one of them upside down. Not sure how to square that with an input volume pot. (I know, why have an MV pot? A: kids with an early bedtime).

I used a 4 cap/dual gang style post PI MV in the last amp I built with a cathodyne and it sounds great, but def has the farting out at high input problem. It's been my main gigging amp for about ten years and works great. But it seems a retrofit grid stopper is in order. The secondary problem is that it interacts with the bias wiggle trem when it's not at full volume.

[didit]

If committed to the Princeton cathodyne PI template definitely follow recommendations on "Stokes" mod along with grid-stoppers.

Best .. Ian

[telentubes]

I altered the layout to make it flow a little better, added another filter cap, and did a few mods from Rob's site, specifically, the "Paul C Mod", as well as adding adjustable bias, phase inverter grid stop resistor, and grid stop and screen resistors were added to the power tubes. The modded amp is markedly better for my needs. Smoother when you turn it up, and the flabby low end is tamed. I'd slow down the tremolo if I used it, but I really don't. I have an Eminence Josh Smith Signature 12" speaker (JS 1250) in the cab, which I recommend. It is my current "go to" amp. I've built them with Mid pots, but prefer just Treble and Bass.

[norburybrook]

Having built a princeton reverb last year in a Trainwreck chassis I'd say the standard version is hard to beat, it's one of my favourite 'clean' amps now. The bass is typical fender farty if you dime it but I use my Tweedle dee for that, so if you're going to be doing that then perhaps look at the telentubes suggestions

Only modifications I did were to double the cap values on the trem so it starts slower in the range, and I fitted a dwell pot for the reverb on the rear of the amp so you can really fine tune it. I made the combo cabinet larger and fitted an Eminence Cannabis Rex 12 inch speaker.

Lovely amp, superb spring reverb and lovely Bias trem


M

[Roe]

I prefer reducing the 3m3 resistor, while tweaking the other values for keeping the dry/wet balance right

[HereToday]

This is a "Princeton-inspired" design that has some of the mods you may be interested in.
- Mid control tone stack
- Adjustable bias
- Adjustable trem
- Adjustable feedback
- DC offset for heaters
- Quiet input section
- Bias measurement resistors
- Mute switch
- Bright switch
- Pre PI MV
- Adjustable speaker out impedance

No Fx section, though. Note, some of the tubes are different from a PR as well.

Schematic here:

[HereToday]

It is an inverted layout so that tubes can reside atop the chassis, but maintain an American controls layout on the faceplate.

This is the layout.

Btown 15R Layout r1.pdf

[mirage_indigo]

That looks great, what program did you use to draw it out?

[HereToday]

I used Visio for both. Actually, I'm a little embarrassed with all the spaghetti in the layout, but I was in a hurry to get to the build. I'm going back now and making the wiring a bit neater. I'll post the revised layout when finished.

Eager to hear how your Princeton is coming along. I imagine you are still in the design phase?

[Heikki]

I recently built Princeton Reverb with few minor tweaks. Tremolo can be quite weak in Princeton so I changed the 1M resistor that couples the oscillator to the bias pot to 220k (R33 in my schematic).

I would not bother with DC heaters. With "low-gain" amp like Princeton decent lead dress and layout is all that is needed to keep the amp hum free.






Schematic

[HereToday]

While making a couple of other as-built revisions, I was able to clean up the wiring in the layout. This should be a bit more pleasant to view. Again, my apologies!