Princeton Mod Placements

[jordan86]

Newbie here. This shelter in place has gotten the best of me....so I'm setting out to finally build my first amp here shortly. 

I am most seriously considering the Princeton Reverb AA1164 (though a 5f6a and RobRobinette's 6v6 Blackvibe are in the running still). I'd like to do two simple mods, but would welcome the advice of more experienced builders as to how the placement of the mods may effect noise.

The two mods I'm considering...

1) Raw Control. I really would like try this. Thinking of using the Ground switch hole on the back side (or extra speaker jack, would be my second choice). Just thinking the mid resistor with the added 100K or 250K pot. Would this placement so far from the tonestack cause any added noise?

2) Moving reverb control to back side of chassis? Again, any issues with noise here? Would probably use the extra speaker jack, or drill a new hole new the reverb tank inputs on back. REASON: This one is more ridiculous, but I just REALLY like the aesthetics of the Non-Reverb Princeton faceplate. A little more open real estate and the logo looks better to me. Totally stupid, I know. Would require a new faceplate too. I may just skip.

Also plan to upgrade the OT to Billm/Allen TO20 but that's nothing too out of the ordinary.

Bonus request: Anyone out there just prefer the Non-Reverb Princeton AA964? I could just build that amp from an AA1164 kit, I think. I'd be content without reverb. Even though its a simpler circuit, I imagine it may be a little more difficult to go "off the page" for a first build. Doug has posted the AA964 circuit on his site and offers an eyelet board. I understand that without the reverb make up gain stage it stays cleaner all the way up the dial, but is only as loud as a PR on 6? Does that sound right? I'm a pedal guy so the clean doesn't bother me. Slightly prefer it.

Thanks in advance to any generous souls willing to help me!!!

[shooter]

how the placement of the mods may effect noise.

If you start with a quiet amp that can be banged n clanged around and still quiet, I doubt the raw will have any effect unless it's hiss from toooo much gain.

If moving reverb wires makes them shorter, AND there was NO noise to start, that shouldn't be an issue either.

flying wires willy nilly, without regard to small signal, big signal WILL insure a good chance at noise

[jordan86]

My Princeton build is coming along smoothly. Wanted to ask about preferred way to tackle a RAW mod. I am going to start with a mostly stock build (Mojo kit) but have both a 100K pot or an extra 68K resistor (i replaced the input resistors with metal film). Doing tonestack calculations on TSC I liked 100K for a pot value, but could definitely be content with 68K if easier to utilize that in switch form.

Would appreciate some guidance on what would be the cleanest/easiest approach:

• Would a 68K on a switch or a 100K pot be an easier mod to implement?
• I'd be content to use the ground switch hole or the ext speaker hole.Is one better?
• Is there a way to utilize the ground switch as is to put the 68K resistor in series?
• Also I'd love to be able to tackle this with just running one wire under the circuit board - NOT like the picture below. Is that possible or do I have to run two wires

FWIW, so far I have all the mechanical assembly done and the circuit board populated. Now to run the jumpers to the back of the board. UGH...not looking forward to that. :)

Going to pass on the Stokes and Paul C for now, but I did a few upgrades/mods right out of the gate, including:

• Hammond 290AX PT (100ma capable vs 75ma)
• David Allen's TO20B OT
• Adjustable Bias pot (10k pot, 27k resistor)
• Replaced first two bypass caps with 4.7uf
• Swapped pne of the .01 trem oscilators for an .022 (only had one extra)
• Swapped 1M trem intensity resistor for a 430K (technically a 470K. I'm happy it measured lower)
• Several of RobRob's "performance" upgrades.(grid stoppers, component upgrades, etc)

Do I have to have two wires for mod like below, or can it connect to the 6.8K in series?

[jordan86]

Update: So I'm no switch expert but I think I figured out how to do a MID/RAW option with the switch scenario. I got my multimeter out and tested for continuity with the switch in different positions.  I think I can do the attached scenario below.  Even tested it with the resistors just dry fit in there to see how it reads out on the multimeter.

Only question would be grounding the resistors. Does my ground location matter? Since the switch is so far from the tonestack, wondering if it would be better to run a ground wire all the way back to tonestack ground bar, or use a closer ground point? Options I have:

• One of the ground tabs attached to the 6v6 power tube sockets.
• Main power ground tab
• Ground to chassis?

Also....Would this scenario work for a single wire run to the ground switch hole using a RAW pot? Was poking around on Sluckey's website and found the diagram of his AB763 Deluxe light.

[shooter]

I've used Sluckeys RAW and it works fine.
use the preamp ground buss, or "fly" the 6.8k to one of the pots that already has a ground wire going to it.

[mresistor]

like he said above..    I really like the raw pot..      I mounted mine in the #2 input on the front panel and then changed the grid stopper to 22K ohms.    It was easy. 


if you mount it in the back by the power tubes it is advisable to use shielded wire for connections.   

[jordan86]

Follow Up ?....

When running shielded cable into AC land, should the shielding double as the ground connection or is it best to run a separate ground connection AND ground the shield at one end?

Scenario: I've place a 100K RAW pot in the unused ground switch of my Princeton. I've just been using the stock tone stack for a few weeks though. Time to actually wire up the RAW pot.

Planning to run one lead from the bass pot to the RAW wiper terminal, then back from the ground terminal on the pot to the 6.8K resistor, connected to the preamp group bus.

Debating using just some cheap 22/2 shielded cable from the local home depot. Our would a 4 conductor shielded cable still be better? Guessing I'd connect two leads per terminal? Like red/black on the wiper terminal and green white on the ground terminal?

Bonus Question: Is it best to float the RAW pot off the chassis (with a plastic washer) to avoid a ground connection there? Assuming it would be ideal for that to ground back at the preamp ground bus to avoid ground loops? Or does that not matter?

[shooter]

I try and never use the shield as "a wire"
as a shield, it gets ONE end soldered, the one closest to the "AC source"

the pot "exterior" is already isolated from the inside stuff, so no ground loop issue there.