Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: J3ona1 on September 23, 2023, 08:45:40 pm
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Hi Folks,
I play out in jam sessions and have found that my 65 PRRI could use a little more volume. I'm building a new Princeton Reverb based on the aa1164 circuit and I'm picking transformers for the build. Will the Stokes mod and a deluxe reverb pt/ot give me that extra bit of volume needed? Are those changes worth the difference in volume it provides in db's? I love the tone of the PRRI (it had an alnico blue loaded in it) and I don't want to change its tone too much. I'm not against using the drop in hammond replacements for the Princeton Reverb pt and ot and just sticking with letting this small amp do what it does best! Sidenote: I purchased a Warehouse G12C for the build.
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I ... have found that my 65 PRRI could use a little more volume. ... Will the Stokes mod and a deluxe reverb pt/ot give me that extra bit of volume needed? ...
No way to know unless you can say for-certain, "I used a Deluxe Reverb, and it was plenty loud enough."
I ... have found that my 65 PRRI could use a little more volume. ... I purchased a Warehouse G12C for the build.
What speaker does your PRRI have now? The Jensen C10R found in the current reissue (https://www.fender.com/en-US/play-home/65-princeton-reverb/2172000000.html)?
I ask because the speaker's sensitivity is perhaps more-important than amp-power in determining how loud you will be. If, "Yes, my PRRI has the stock Jensen C10R," then you might be loud enough with the new G12C speaker and no circuit-change.
PRRI 15w into Jensen C10R (https://www.jensentone.com/vintage-ceramic/c10r):
10 log (15w/1w) + 93.6dB = 105.4 dB SPL
Deluxe Reverb 22w into Jensen C10R:
10 log (22w/1w) + 93.6dB = 107 dB SPL
Super Reverb 40w into Jensen C10R:
10 log (40w/1w) + 93.6dB = 109.6 dB SPL
PRRI 15w into Warehouse G12C (https://wgsusa.com/g12c#specs)
10 log (15w/1w) + 99.48dB = 111.2 dB SPL
From the above, playing the stock Princeton into the G12C is likely louder than playing a 40w amp into the relatively-insenstive C10R speaker. So the loudness-change from just doing the speaker-swap will very likely outweigh the Deluxe Reverb parts of the phase inverter circuit-tweak (though if you made all the changes at once you might not realize the speaker was responsible for nearly all the loudness-change).
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1. My PRRI was loaded with a Celestion Alnico Blue. What I think I'm hearing is that a more sensitive speaker is more effective and less expensive in cash/elbow grease to accommodate those transformer upgrades.
2. If a deluxe reverb ain't loud enough then my amp just won't be loud enough.
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1. I've never played a DR out, but in shops I've always found them a bit TOO scooped for my liking, and I loved the warmer tone of the princeton. ...
You're probably reacting to the bright cap on the Vibrato channel Volume control, which makes the Deluxe Reverb sound "steely" unless you have the Volume up to 7-8. I hated that aspect of the 1964 Deluxe Reverb I used to own.
2. My PRRI was loaded with a Celestion Alnico Blue. ...
The Celestion Blue is a 100dB speaker (https://celestion.com/product/celestion-blue/), and slightly more-sensitive than the G12C. So if it's not loud enough, you won't get the volume-boost I described.
I play out in jam sessions and have found that my 65 PRRI could use a little more volume. I'm building a new Princeton Reverb based on the aa1164 circuit and I'm picking transformers for the build. ...
3. If a deluxe reverb ain't loud enough then my amp just won't be loud enough.
It sounds like you've already decided to build the Princeton circuit. You can do the transformer and Stokes-mod changes you asked about, and you will get marginally more volume. You're already using a 12" speaker, so that change is off the table.
Depending on your applications, I'd recommend adding a Middle control as I find that very useful.
(Of course, I also tend to turn the Bass control down to 1-2 on blackface amps, and would spend more time/energy trimming values of cathode bypass caps & coupling caps to shave the excessive bass. But that extra bass sounds good playing solo at home.)
Having owned a bunch of blackface amps at the same time (https://i.imgur.com/zYh0eyF.jpg), I'd choose the Pro Reverb or Super Reverb power-level to have any kind of chance at a clean-ish sound in a band setting, then augment with a good dirt pedal or two.
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HBP. You're the man.
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Hi Folks,
I play out in jam sessions and have found that my 65 PRRI could use a little more volume. I'm building a new Princeton Reverb based on the aa1164 circuit and I'm picking transformers for the build. Will the Stokes mod and a deluxe reverb pt/ot give me that extra bit of volume needed? Are those changes worth the difference in volume it provides in db's? I love the tone of the PRRI (it had an alnico blue loaded in it) and I don't want to change its tone too much. I'm not against using the drop in hammond replacements for the Princeton Reverb pt and ot and just sticking with letting this small amp do what it does best! Sidenote: I purchased a Warehouse G12C for the build.
I personally find the 12” blue in my PR is adequate volume for most of my playing.
For Transformers i’d recommend the Soursounds transformers. Especially the reverb one transformer. Bryan has replicated the factory and then added a secondary winding in it so you can use either normal factory dwell or a lighter dwell. You can then add a switch to toggle dwell in place of the ground switch.
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... the reverb one transformer. Bryan has replicated the factory and then added a secondary winding in it so you can use either normal factory dwell or a lighter dwell. ...
It's easier & more effective to attack the Root Cause: use a 100kΩ audio taper Reverb pot, rather than the 100kΩ linear taper indicated in the schematic. Now the amount of reverb you previously got at "3" has been moved to "7" on the dial.
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Not really part of the original query, but regarding the reverb dwell thing;
After broaching that subject here years back & trying it out, I have added a dwell control whenever possible, as I find it makes the reverb way more adjustable. A pretty nice return (pun partially intended, as it's really the "send") for changing out 1 part for about $3.
Still surprised it wasn't included in the original circuits.
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... the reverb one transformer. Bryan has replicated the factory and then added a secondary winding in it so you can use either normal factory dwell or a lighter dwell. ...
It's easier & more effective to attack the Root Cause: use a 100kΩ audio taper Reverb pot, rather than the 100kΩ linear taper indicated in the schematic. Now the amount of reverb you previously got at "3" has been moved to "7" on the dial.
I have not tried that mod. That just changes the curve for mixing in the wet signal as opposed to dwell though. Idea being mix in less of the same dwell versus change dwell? Not in disagreement on which is easier just seems like two different outcomes.
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... That just changes the curve for mixing in the wet signal as opposed to dwell though. Idea being mix in less ...? ...
Yes.
The 6G15 Reverb has a Dwell control and a Mix control.
Certainly it seems desirable to turn down "Dwell" when your Mix control is stuck near full-up (as is the case with a linear-taper Reverb control). Once you are able to "turn the Mix down" (with an audio-taper Reverb control) you will likely find the Dwell control has lost some of its appeal.
FWIW, I own a 1965 Reverb unit. Dwell is useful, but Mix is more-critical.
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My personal recommendation would be to go with whatever transformer set allows you to use 6L6s in the Princeton. A 40w Princeton is a thing to behold.
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A 40w Princeton is a thing to behold.
Isn't that the first Mesa Boogie?
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A 40w Princeton is a thing to behold.
Isn't that the first Mesa Boogie?
Yes and he stole the reverb tube for the extra gain.