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5e3 to bare bones PRRI conversion?

Discussion in 'Amp Tech Center' started by regispenguin, Aug 19, 2020.

  1. Dacious

    Dacious Poster Extraordinaire

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    Rather than reinvent the wheel, and end up with a flat on one side, take the advice of people on this page.

    The PRRI is a Princeton Reverb. It just has PCBs instead of a hand soldered tagboard, but the circuit is the same.

    A PR is a Princeton with reverb.

    A Princeton is a smaller Brown Deluxe with 10" speaker and tremolo.

    A Brown Deluxe is a Tweed with fixed grid bias instead of cathode bias.

    So if you build a 5E3 it's the simplest and.lightest 6V6 push-pull amp that's very easy to build because it's cathode biased.

    Once you have built a 5E3 you can progressively turn it into a Princeton - the 6G2 Princeton is probably the most revered small Fender. Even more so amongst cognoscenti than the PR. Fender builds a $3000 handwired version of this, the Chris Stapleton.

    And it has a direct lineage to a Tweed Deluxe.

    The Tweed Deluxe power and output transformer are straight into the ballpark for a 6G2.

    So if you build the 5E3 and get it working - and it's a great amp, built two myself - it's about a dozen components and half a dozen circuit changes. It has the right number of tubes, too

    You can build a 5E3:with a single input in a small chassis. Very easy. Someone posted a link to Rob's version.

    If you build a PR with no reverb or trem, you have a Princeton with no balls, because the PR uses a tube to push gain up because the reverb tank and circuit pulls it down.
     
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  2. Wally

    Wally Telefied Ad Free Member

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    Ime, a BF/SF Princeton no-verb is NOT a 6G2....very different results due simply to the difference in tone stacks. The 6G2 will make a Bf/SF non-verb Princeton back off, ime....6G2s are great little amps. The tone stack in the BF/Sf holds the BF/SF amp back from getting as lively as does the 6G2.
     
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  3. regispenguin

    regispenguin TDPRI Member

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    love uncle Doug. I understand a lot of what he says but not to the extent where I can confidently say I know what changing out resistor and cap values. I think I’ll need to do hands on experimentation to get that kind of understanding.
     
  4. regispenguin

    regispenguin TDPRI Member

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    I like the comment about the Princeton no reverb being castrated. That was a big reason for my initial question so thanks for confirming that.
     
  5. Wally

    Wally Telefied Ad Free Member

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    yes, the PRin Rev has a third gain stage. However the gain effect of that stage is not full force because as noted the reverb and vibrato circuit eat a lot of gain. if one builds what you described first, which is what D’tar showed us on page 1 and which is also a Champ II amp, you get those three gain stages that are full strength...and the amp is in effect an AB 165 Bassman Normal channel. You get. A hot amp. A 5E3 with a gain sucking tone stack doesn’t have much go power in the preamp. I know that I would not want that type of amp. Ymmv.
    The question is, imho... “what sound are you looking for?” What have you played that you would,like to have?
     
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  6. jays0n

    jays0n Tele-Holic

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    Agree totally. Next step must be to try a simple build. I hope to would keep it very simple as some are recommending in this thread.



     
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    regispenguin and D'tar like this.
  8. jsnwhite619

    jsnwhite619 Friend of Leo's

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    I'll throw my 2 cents in here. I actually never played a Princeton Reverb until I built one last year. Until then, I assumed that maybe the LTP phase inverter was what really set the different tone with Blackface amp vs the Tweed amps I had built and played up to that point. As soon as I plugged in, I realized I was wrong. That Treb/Bass tone stack is what does it, to my ears at least. So, if that's the tone you're after, I don't think anything with a simple Vol/Tone setup will be a real substitute.

    Rob's PR -trem -reverb all stuck into a 6g2 chassis might be a good smaller configuration that meets the requirements.
     
  9. schmee

    schmee Doctor of Teleocity

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    Just build a BF Princeton (Non reverb) layout. I did this recently in my Monoprice 15 chassis and cabinet which is a bit tighter than the 5E3. It was a PITA but I got it done. You can choose to not do the tremelo if you want, although it doesn't lessen the number of tubes.
     
    Last edited: Aug 23, 2020
  10. zook

    zook Friend of Leo's

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    My 2 cents:

    A Princeton is not a 6G2 since they have different Phase inverters.

    Here's my comment on Rob's schematic

    upload_2020-8-23_8-14-18.png
     
  11. zook

    zook Friend of Leo's

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    A Princeton has a cathodyne phase inverter, The Brown Deluxe has a long tail pair

    Tweed Deluxe has a cathodyne PI
     
  12. Dacious

    Dacious Poster Extraordinaire

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    True - I know that. I had a SFPR built a couple 5E3s and have a 83 Superchamp. Owned Pro Reverb and Vibrolux Reverb.

    I was meaning more in conceptual terms. The OP is not across the distinction.
     
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  13. schmee

    schmee Doctor of Teleocity

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    The Princeton and PR Cathodyne PI is the magic if you ask me.
    It would be great in a 5E3 chassis.
     
  14. Dacious

    Dacious Poster Extraordinaire

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    That's why I got the Superchamp. Princeton preamp with cathodyne PI with ballsier PT into .Deluxe Reverb output transformer.

    Touch sensitivity and reverb into solid giggable 18watts.

    If I were the OP I'd just go 6G2 - it's what I'd build. Vintage one with a 67 Tele in Cargill, best single Fender combo I've ever heard. Shop owner had just unboxed it in his store.
     
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  15. printer2

    printer2 Poster Extraordinaire

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    [​IMG]
    [​IMG]

    A 6G2 is not much different than a BF Princeton non-reverb. Ignore the trem on either and you have the same amp. Now the difference between the BFPNR to the PR is the triode used to do the trem. You could easily convert the 12AX7 into the reverb recovery triode. Assuming you can do that on the nonreverb you can do it on the 6G2 if you can make a little perf board for the tone stack parts.

    So really they are all the same amp but just a few things modifying them.

    I will get back to this yet, need my other computer.
     
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  16. printer2

    printer2 Poster Extraordinaire

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    Now the 5E3

    [​IMG]

    Stick the tone stack where the volume and tone circuit is (disconnecting the normal volume control) and you have the above BF circuit. Well, almost. You need to get rid of the 250R resistor and capacitor and replace it with the fixed bias. Since The 5E3 does not have one you might as well make a little adjustable fixed bias board and have it sit where the 250R and 22uF cap sat. So now you have a BF non reverb.

    You only need to put the volume control go into the Normal triode ans when it comes out off the plate go through the 3.3M resistor and cap. To be acurate you would add the other parts preceded and behind it as Rob showed. Easy right?

    Well depends on the execution. I could probably do it on a 5E3 board with those instructions, Wally no problem, a few others here. I can't say that about everyone but it is doable. I was going to do something else, seems I did not need the other computer.

    Oh wait, forgot about the NFB for the 5E3, another little change. Might be worth making up your own board at this point. But I see no reason it could not fit in the 5E3 spot.

    More looking. I think a 6G2 board, use the Volume and Tone position for the reverb 3.3M, then use the Trem triode for the first stage and the tone stack parts. But still the NFB 49R resistor is missing, feels like I am going round in circles. Sorry. Mind you, that is how I get from here to there. Iteration after iteration til I get what I want, in my head that is.
     
    Last edited: Aug 23, 2020
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  17. printer2

    printer2 Poster Extraordinaire

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    Here we go. Not too hard. I was going to use some whiteout and mark up Fender's 5E3 layout but I don't have any that is not rock hard.

    1. You do not use the second set of inputs, just the one at the edge of the board. you do not jumper across the cathodes of the input tube. Pin 2 will go to the regular resistor/capacitor combination but rather than 820 ohm you put a 1.5k. The 68k input resistor positions for the second channel, you are going to use this for the second stage 1.5k cathode resistor as well as the 22uF cap. You jumper the other end of the parts together and then run a jumper to the ground point of the input cathode bias pair. Now both triodes are biased properly and act independently.

    2. Replace the second channel volume and tone pot with 250k pots. You are going to copy the Princeton arrangement but rather than having the 100k resistor and the 0.047 and 0.100uF capacitors on the board you are going to solder one end of the capacitors to the pots and the other ends to a perf strip or whatever you find convenient.
    a) Where the 0.005 uF capacitor was soldered to the tone pot (now to be the bass pot) is where you put the 6.8k resistor for the tone stack.
    b) The middle of the bass pot goes to the closest lug of the treble pot (which was the volume pot).
    c) The middle of the treble pot goes to the far lug (closest to the input jacks) of the volume pot.
    d) The 250 pF cap gets soldered to the top lug of the treble pot. e) The 0.047 uF cap soldered to the bass lug with the resistor.
    e) The 0.100 uF capacitor is soldered to the center lug of the bass pot.
    f) On the perf board (which is conveniently mounted by the controls) you are going to join the 0.047 uF, 0.100 uF capacitor leads together and to one side of the resistor.
    g) The other end of the resistor is going to be joined to the free end of the 250 pF capacitor. This point will then go to the first stage 0.100 uF coupling capacitor.
    h) The center lug of the volume pot is wired to the second triode grid.
    i) Congratulations, the hard part is done.

    3. The 0.100 uF coupling cap now goes to the 3.3M resistor and 10 pF capacitor, I probably would ignore the cap. Rob has the parts that went to the reverb in place, I would ignore them, the 470k resistor to ground after the 3.3M, I would use. Or not. There is no reason the 3.3M can not be a 1M, might as well use the one from the unused input. And since we divided that by a third we want to do that to the 470k, so that now will be a 150k. This should reduce the noise a little, will anyone notice, let us know. A handy place to put these two resistors might be between the 0.020 uF and the 0.100 uF coupling caps. Run the ground to a convenient place. Take the reduced signal from between the resistors and wire it up to pin 2 of the second triode.

    4) Here is the tricky part with the NFB. Rather than just the 1.5k resistor with the 22 uF cap across it you are going to twist the leads from the 1.5k resistor and a 47 ohm resistor together and solder them. Then solder the pair across where the 1.5k resistor originally was. You need to solder a 2.7k resistor on the speaker output jack to a standoff or whatever you creatively come up with. Then you wire the end of the resistor to the 47R/1.5k junction.

    5) Install 470R resistors on the 6V6 screens (Or not, I would)

    6) Look up a fixed bias board to get the bias off the high voltage winding. Change the power supply capacitors and dropping resistors to increase the stiffness of the power supply,

    7) Sorry for the rush on 6) but it is movie time.

    I think that is it but I will check it over tomorrow.
     
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  18. printer2

    printer2 Poster Extraordinaire

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    Movie was ok. Just noticed Rob's layout has a bias board. Don't have to look for one. Thinking about it replace the 5Y3 with a less lossy rectifier will give a bit more voltage and less sag.
     
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  19. mgreene

    mgreene Tele-Afflicted

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    There is however something to be said for the Non-reverb's ability to take pedals. So far, mine is the ultimate living room amp.
     
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  20. Wally

    Wally Telefied Ad Free Member

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    It seems that time has proven by usage that all BF preamps take pedals well.
     
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