Swapping Princeton Reverb built with Deluxe PT & OT to Standar

[daveneary]

Hi,
  I built my first Princeton reverb Sept/October time last year. I used the deluxe reverb Power and Output transformers.  I want to try putting original spec PT and OT's in.  Are there any pitfalls, I am hoping the swap will get some breakup in the amp. Which will have the biggest impact on the sound - smaller PT or Smaller OT.
Dave.

[pompeiisneaks]

I may be out on a limb here, but I think both impact tone.

PT if not quite delivering fully what the circuit wants can create more sag.  This won't necessarily change the break up, though, I don't think.
OT, if under powered, I think will just get hot and can burn up, its just pushing the sound you put into it. 

I think the break up is based upon the biasing of the tubes.  Now the overall voltages may be lower thereby adjusting the bias of the tubes anyway, meaning the overall tonality of each stage is adjusted as well, so that means the PT has another impact as well. 

Maybe the guru's will set me straight if that's off...

~Phil

[Shack]

I would think the 8k ohm output transformer would get it closer to the PR sound and breakup than the power transformer ....the DR output transformer is 6.6k ohms and from what ive been told here, that makes alot of difference...seeings how the PT isnt far off in B+ voltage....maybe current capacity is the only difference there.

[CraigB]

Hi,
  I built my first Princeton reverb Sept/October time last year. I used the deluxe reverb Power and Output transformers.  I want to try putting original spec PT and OT's in.  Are there any pitfalls, I am hoping the swap will get some breakup in the amp. Which will have the biggest impact on the sound - smaller PT or Smaller OT.
Dave.

Hey Dave, nice avatar!  You're fine using the spec xfmrs.  I think the overall effect is bound to be more heat, a little less output power, less bottom end with the smaller OT, and if you really like to crank it up, you'll likely get breakup slightly earlier.  To me the downside would be the chassis cutout for the PT is probably not going to be the right size.  You could always start with the OT swap and see how you like that

[mresistor]

I would stay with the bigger iron and not look back. I love my Hoffman PR with oversize PT and deluxe OT.   Hands down way better than my stock 1978.  Much more headroom, ability to use EL34/6L6 and takes pedals effortlessly.

[eleventeen]

Have you tried changing out your first preamp tube (or perhaps others) to a 12AY7, 5751 or even a 12AT7?


I'm not sure exactly what you are aiming at tonewise and probably could never be, given (only) a written description. But depending upon how much metalwork this proposed change will force you to do.... I mean, if you have built up a full-on complete clone unit on nicely drilled and machined chassis....and now you'll have to fabricate some sort of adapter plate for the PT AND very carefully drill for the smaller footprint OT----because the mounting holes are very closely spaced astride the parts board....the electronic connections to be remade are pretty trivial....


All I am saying is, it would be a sin to start off in this direction if you could get what you wanted via a perfectly reversible tube swap.

[daveneary]

Thanks for the response so far.  Tone wise - I love the tone of the existing Princeton Reverb with the deluxe xformer but it won't break up. I have tried swapping the reverb driver between 12AX7 - 12AT7. I want to avoid pedals if I can but I have a Bluesbreaker II which is OK but not great. 
I  have purchased a second princeton chassis so am thinking of  ending up with a Princeton Reverb with orginal spec Xformers and building a single channel Deluxe reverb  - keep one as a head and the other as a 12" combo to suit. 

I will need to drill to fit the smaller PT in the existing Chassis. I will tryout to see how that sounds before deciding whether to swap out or keep the larger OT.

The Champ OT I have purchased only has 2 input wires (Blue and Black) the existing DR one has a Centre tap which goes to the B+. Can I create a centre tap with 2 resistors going to the B+ ?

Dave

[jjasilli]

Intead of iron, you can try more gain.  Checkout "Torres Mods". Below is my my hotrodded Princeton schematic which incorporate those mods & more.  A RAW control alone will probably cause overdrive. 

[eleventeen]

"Thanks for the response so far.  Tone wise - I love the tone of the existing Princeton Reverb with the deluxe xformer but it won't break up. I have tried swapping the reverb driver between 12AX7 - 12AT7."


This is not the grail tube swap, this only affects the reverb drive, not the "dry" signal. You want to try a lower gain tube (12AY7, 5751, 12AT7) for V1, the very first small tube in the amp. With a lower gain first-preamp-tube, the immediate effect will be, you'll have to crank the volume control higher to get the same output level. The idea is, if you had to crank the vol control using the original tube to let's say "8", the tube swap will cause the amp to breakup more at "5". This theoretically gives you more rotation of that knob during which the amp breaks up.


"The Champ OT I have purchased only has 2 input wires (Blue and Black) the existing DR one has a Centre tap which goes to the B+. Can I create a centre tap with 2 resistors going to the B+ ?"


No. A champ OT is what's called a "single ended" output tranny, (abbrev: "SE") used for a single-tube output section, in this case, a single 6V6 (or could be a 6BQ5 or 6AQ5) A Champ OT is very much like the reverb driver tranny you currently have, using the two sections of the 12AT7 strapped together to drive the reverb can. It otherwise has no applicability to a dual-tube aka "push-pull" output section.

Once again, there's no way I can predict whether this suggestion will give you what you want, whatever that is. What I am advocating is to flip the tubes on the grounds that it's easy to do and easy to reverse. Plus, knowing this and knowing the results, perhaps you use a 5751 playing in the bedroom but change back to a 12AX7 doing a small gig. That would be somewhat useful, I think.

[p2pAmps]

I have built quite a few Hoffman style turret style PRs and I have used Classic Tone PR PT and a DR OT with great success.  I have not heard one customer complaint so far.  In fact they are rave how this is the best sounding PR they have ever played.

My 2 Cents

[ac427v]

I'd like to know more about your amp. I suspect plate voltages are too high for the sound you want. Can you give voltage readings on all pins on all tubes? Also what are you using for a rectifier? I'm a fan of increasing dropping resistors and using a 5R4 rectifier to reduce voltages and increase breakup/distortion.
--alt Craig B

[daveneary]

I will look at this at the weekend - and report back.

[Ed_Chambley]

Try putting your NFB on a switch.  This will make the amp breakup sooner.  Also, usually when using a Deluxe set of iron the Princeton AA1164 Circuit gets too boomy so most people reduce the bass a lot.  Reducing the first Bypass cap to 4.7uf - 6.8uf will help as well.


A raw control will help as well.


Since you have this iron, you should be able to Run 6L6 tubes.  When I use mine for a show I install some Tung-sol 5881's and bias for these and it turns into a real amp.