My Princeton Reverb Build

[dragonbat13]

Here are some pics of my Princeton Reverb.  First complete build.  Changed the Reverb Pot to from liner taper to audio taper and slowed the vibrato with a cap swap.  Very happy except for the cranked overdrive.





The overdrive does not sound as though there is something wrong with the amp, it just sounds like the type of overdrive thats not right for me.  Of course I have not been able to play a humbucker equipped guitar with it. 

[sluckey]

Looks very nice.

[Willabe]

Very nice! 

......Very happy except for the cranked overdrive.

The overdrive does not sound as though there is something wrong with the amp, it just sounds like the type of overdrive thats not right for me.

Read this, might be/probably blocking distortion, Merlin shows a fix for it;

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

[dragonbat13]

Looks very nice.

Thank You.  It has a Jenson Special Design Alnico 10 in it and some of the last of the classic tone transformers, Princeton Reverb Spec.  Mojotone cab and chassis.

[dragonbat13]

Very nice! 

......Very happy except for the cranked overdrive.

The overdrive does not sound as though there is something wrong with the amp, it just sounds like the type of overdrive thats not right for me.

Read this, might be/probably blocking distortion, Merlin shows a fix for it;

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

I kinda figured that is what it was.  Ill look into it.

One other note regarding the parts in the amp.  I do not like the ceremic sockets at all.  I had to change the first preamp socket out because of bad connections.  Put in a Belden.  Eventually I will replace all the sockets.  But I cant stop playing it enough to give time for that!

Overall a wonderful amp, even though I found why its not recommended for a first build.  I have a lot of amp repair experience so I wasnt worried about if I could build it.  But it would for sure be a challenge for someone with less experience.  And I still wish I would have built something less complicated just due to the fact of things I found I prefer that I did not implement into the amp, such as the socket issue.

[tubenit]

I'll offer a thought for your consideration.  I owned an original PR.  I loved the clean tone.  I disliked the amp when overdriven and thought it sounded harsh even after an alnico speaker change.  So, I got rid of it.


Over the years, I've done quite a bit of experimenting to see what contributes to a smoother overdrive tone that I would like. So, I will offer these ideas for your consideration.  NOT saying you should do these.  However, I think you might find the amp sounded smoother when you pushed it into overdrive if these component values were changed. 


I have not done this myself with a Princeton Reverb.  But I currently have an amp that has 3 gain stages into an LTPI where I have it set up in a similar manner with similar values.  And if I were to build a Princeton Reverb, this is how I would approach it. I'd likely end up with a 12AY7 in V1.


You may also wish to consider 1.5k grid resistor on the 6V6's similar to a Deluxe Reverb.   


With respect, Tubenit

[acheld]

I think you might find the amp sounded smoother when you pushed it into overdrive if these component values were changed. 

Curious about some of these changes suggested around the PI:   You have a 220pF capacitor in parallel with the 56K plate resistor for V4a; what does this do?  Followed by the .047uF coupling caps to the output tubes (these are normally 0.1uF for a PR) -- how does this deter unpleasant distortion?

[SILVERGUN]

Ill look into it.

This is where a scope is an absolute necessity. You can look at your signal and see what it is you're not liking. You can make sure that your new build is working correctly. Then you can see what differences your tweaking makes.


On a separate note. I have an old Deluxe Reverb. I love the gritty cleans and the reverb. I wasn't a big pedal guy until I learned how to use one to push the DR right where I want it. Volume at 4 (40%), bass on 2, treb on 6 and that is my base tone (edge of breakup). I use one boost/overdrive pedal to create my crunch/rhythm tone, and another overdrive in front of that set for a volume boost to go over the edge for leads. This is my Friday night beer drinking with the boys basement rock and roll rig.


The key with any overdrive or distortion is to leave the distortion setting low'ish and drive the amp with the gain/volume setting.
Try that before you go changing a perfectly good amp. (said the guy who has changed every single perfectly good amp he has built)

[tubenit]

Curious about some of these changes suggested around the PI:   You have a 220pF capacitor in parallel with the 56K plate resistor for V4a; what does this do?  Followed by the .047uF coupling caps to the output tubes (these are normally 0.1uF for a PR) -- how does this deter unpleasant distortion?

Regarding the 220p, there is this thread about the "enhance cap".  Smoothing "Enhance" cap (el34world.com)


Regarding lower values like .047 instead of .1  .................. and also 10uf, 5uf, 2.2uf instead of 22uf,  these changes give me a smoother overdrive.  My guess is that it changes the frequencies being overdriven and that somehow smooths the overdrive tone to my liking.


Note on Dumble amps, Cornford and Mesa Boogie (and others that are more overdriven in tone) that they often use some smaller value cathode caps and coupling caps than the typical Fender amps.


With respect, Tubenit

[sluckey]

Followed by the .047uF coupling caps to the output tubes (these are normally 0.1uF for a PR) -- how does this deter unpleasant distortion?

A .047 cap passes less bass to the output tubes than a .1 cap. Less bass means less flub and distorted bass flub doesn't sound good. The same goes for using smaller cathode bypass caps in the preamp. Although the preamp tubes, especially the first one, don't really distort that much, with a big cathode bypass they will pass more bass frequencies on to later stages that do distort and distorted bass just doesn't sound good.

[tubeswell]

But it can be a good thing to have full cathode bypass in the V1a stage to get a good S:N ratio for the input signal, and then manipulate the frequency filtering after that. You can always take bass out, but if you start with poor S:N, the noise floor can become irritating (depending on what you want to use the amp for) YMMV.

[dragonbat13]

When I get a little more time when the rainy season starts around here I am gonna look more into it.  Thank you for all the suggestions, and in the meantime I am going to educate myself on those recommendations so I know exactly what's going on.

But I will say this,  I did not build nor expect this amp to be an amp with overdrive qualities.  I built it so it would be a little more of a lightweight version of my twin reverb.  I was on the fence on what clean, all around amp I should build and this one seemed to fit the bill.  Even down to the ten inch speaker.  I didn't build it to be something it isnt, thats another build which is leaning towards a Dual 50 (Sluckey).  I want to say that the final decision was made after I found that a lot of Steely Dan recordings featured Princeton Reverbs, although I may be wrong.  In any case,  It is a wonderful amp and I am very happy with it. That said I am still going to look into the suggestions so I can fine tune it. Thank you for all the help and insight.

[tubenit]

Larry Carlton used the 5E3 tweed Deluxe for all of his work with Steely Dan

With respect, Tubenit

[dragonbat13]

Larry Carlton used the 5E3 tweed Deluxe for all of his work with Steely Dan

With respect, Tubenit

So I have been proven wrong!

Well it still sounds like something that should be on a Steely Dan album!