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Help: 65 Princeton Reverb Kit Build Problem

Discussion in 'Amp Tech Center' started by trber, Dec 28, 2019.

  1. trber

    trber Tele-Meister

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    Thanks for the response. I was wondering since you had recommended the lower dissipation %, so thought you might have noted the differences in settings. That's great info, and if I get real curious, I'll test it out and see, or ask in the forum, as suggested.

    Many thanks on all the help!
     
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  2. trber

    trber Tele-Meister

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    I am calling this thread resolved, and I am super appreciative for all the help and patience from the contributing forum members. You guys rock!

    To sum up of the good of the order and any future builders who have the same problem:

    1) The unpleasant distortion is gone with a tube change and some messing about with the lead dress. I did not install anything to remedy the problem, as some noted on the linked forum threads.

    2) I installed a 10k adjustable bias pot in the ground switch location with the 22k resistor previously located on the bias board. This gave me enough adjustability to get to 70% dissipation and plenty of room above and below this for fine tuning.

    I am now playing and enjoying the amp quite a bit!

    Thanks for the generous sharing of information and guidance from all you guys. That was a really great experience for me. Cheers.
     
  3. BigDaddy23

    BigDaddy23 Tele-Holic

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    Well done, mate!

    Whatcha building next?
     
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  4. trber

    trber Tele-Meister

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    :D I know, right? Amp building is kind of captivating and rewarding!

    I wish money were no object, but...

    I have looked at the Hoffman site and noted that there is a turret board and diagram for a point to point Blues Junior conversion! Since I already have one of those amps, well, maybe hand wiring it could be interesting! ;)

    Thanks for all the help! It really was!

    Cheers
     
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  5. dan40

    dan40 Tele-Afflicted

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    Hoffman boards are laid out slightly different than most but they are top notch quality. You can also load your own specs into his board maker and he will drill and populate your own custom designed board. Congratulations on wrapping up the build successfully and learning quite a bit in the process!
     
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  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I am sorry if I added to the confusion. I should have explained the reasoning for the suggestions I made. You now know a 10k pot in series with a 22k resistor will adjust from 22k to 32k. Somewhere between 22k and 32k will get the bias required for this circuit. (we now know somewhere between 27k and 32k).

    At the time, you did not want to wait for ordered parts to arrive and you wanted to address a extremely hot bias. I suggested using resistors you had in your possession to come up with a bias in the 50 to 70% range. You had enough resistors in your stash to get into that range.

    (As I mentioned, there are two Princeton AA1164 schematics. The schematic on Robinette's site shows a 5u4 rectifier with a 22k resistor in the bias supply. The other schematic shows a gz34 with a 27k resistor. Your use of a gz34 would indicate a 27k value. (different rectifier tubes provide different B+ voltages which you "now" know effects the bias).).

    To achieve a 27k value, I suggested paralleling two of your 10k resistors (=5k) in series with the 22k to come up with 27k. The bias was still over 70% so, I suggested clipping out one of the 10k resistors. (10k and 22k in series equals 32k.) At 32k you had the cold bias you mention above. I then asked you to parallel in another resistor you had on hand to warm the bias which you did not do. The hunt for a set of resistors to get to a 50 to 70% bias ended there.

    So, yes the 10k is "causing/contributing to the strangely low bias". 10k in series with the 22k equals 32k. (You now have a 10k pot replacing that 10k resistor. If the pot is adjusted to 10k resistance you would have the same strangely low bias.)

    As pointed out by others there is a relationship between the 100k resistor and the "22k" resistor. Those two resistors "fix" the bias in this circuit. To change the "fixed bias" either or both resistors value need to change. You have chosen the ability to quickly change the value of the 22k resistor by adding a 10k pot in series. (the 10k pot is used as a variable resistor).

     
  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Which tube are you using now?
     
  8. trber

    trber Tele-Meister

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    This is great, thank you! It's a super clear explanation of what was happening. It seems I just needed some adjustability within the 32k of resistance, not that that number alone was a problematic value.

    Your time, patience, knowledge, thoroughness, greatly appreciated. I now have an amp I'm really enjoying and growing understanding about how it works. All wins.

    Sent from my SM-G955U using Tapatalk
     
  9. trber

    trber Tele-Meister

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    I just grabbed a tube to see if it would solve the problem at a local, small music store. It's a Mesa/Boogie tube, but not sure who makes those. Eventually, I'll make some choices about brands. I'm just thrilled it's working right now!

    Sent from my SM-G955U using Tapatalk
     
  10. trber

    trber Tele-Meister

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    [emoji106][emoji106]

    Sent from my SM-G955U using Tapatalk
     
  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Glad to help. I learned some valuable info about the Princeton as well.

    I think it's great you stuck with it and gave the resolution.

    Since your next amp build has to wait for financing, you can turn to the next learning experience.

    May I suggest you build two stompboxes? You already have the skill set to build these. You can listen on youtube and find building instructions by googling tagboardeffects crunchbox and tagboardeffects paul trombetta bone-machine. The crunchbox has a useable eighties vibe. The bone machine is a versatile fuzz. These two will build your skills with opamps and transistors. You can learn about low and hi pass filters, and the interaction of diodes for distortion. A bonus is these usually work well with other pedals.

    Use sockets for the opamp and transistors to protect them from soldering heat. Use sockets for the led/diodes so you can try different combinations of diodes for voicing. The opamp and transistors are fairly generic and can be replaced with similar more available less expensive items.

    Crunchbox
    Replace the LM833 with a TL072. Make sure to get the thru hole model not the tiny smd.
    5mm red led can be replaced with 3mm red led. You can try combinations of diodes 1n914 and 1n4001 and green led for asymmetric distortion.(I ended up with two red led but you can hear the differences by using other combinations).
    You can run this at 9 or 18volt if you order capacitors rated above 18volts.
    Instead of the 20k trimpot use a pot (a 50k pot with a ~50k resistor soldered from pin 1 to 3) This allows adjustment from outside. Label it glass or shimmer or presence.
    All of the pots can be log. The 10k pot does not have to be reverse log.

    Bone Machine
    Q1 use 2n5088 and Q2 use 2n3906. A germanium (ge) PNP can be used for Q2. I find it sputtery and low volume YMMV.
    Capacitors C2 22n C4 220n.
    D1 and D2 1n914 and or 1n4001 or similar. Try different diodes to taste.
    The pots can be log.

    If stompboxes are not of interest, you can readily challenge your patience and fine manual dexterity with winding pickups. Yes, I am serious.

    Enjoy your new amp! (Any and all pictures of your finished Princeton would be nice.)
     
  12. trber

    trber Tele-Meister

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    Great information here! I did notice a few differences from what I was seeing elsewhere, so was just making note until I understand how/why the differences exist. Who knows, maybe someday I'll actually be able to use the board maker and know what the heck I'm up to! :D Thanks, Dan. In some ways, the long lead up to finally completing the project has made it that much more sweet in the end. Cheers.
     
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  13. trber

    trber Tele-Meister

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    Umm.....

    That's an emphatic and enthusiastic YES. Great suggestions (pickups, as well)!!!!

    I have seen stompbox kits before, but was never really drawn to them in the same way as an amp build. But, following up with one after the amp project is perfect timing. The fuzz pedal, in particular, has my attention and I'll be planning on that first. Very cool! I've already looked at your recommended searches and watched some videos. Nice.

    Do you have a preferred source to order the box and components? I will be able to look it up, but sometimes, people have preferred sources that may never/slowly come to be known. Hoffman's site, case in point.

    On pickups: that has actually gotten my attention previously. Winding pickups had some strange allure for me. It started with a muddy neck pickup on my Les Paul and after researching a bit, I became fascinated with the huge range of player preferences and options. I settled on a well reviewed but affordable, non-"boutique" brand, but was underwhelmed with the results. Plenty of tinkering with pup/pole height adjustments left me with avoiding using that pickup. Hah.

    I was a bit put-off by the equipment/time investment to make them...winder, trial and error with results, installation challenges (non stop bar guitars are a bit harder to swap pups), and so on. Maybe that's not worth focusing on? Would you recommend I just research "hand winding pickups"? Other? I'd really like to use my neck pickup more! Laughing...

    You're on point: continue the learning experience...thanks for the guidance and suggestions. Looking forward to these next steps!
     
  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    We are off topic for this thread. Should we start a new thread on one of these topics or discuss this privately?

    Components - For your first stompboxes you might just want to deal with one source. I am a shopper, some would call it cheap. Mouser, ebay (pu magnets),(knobs, power jacks, from china), any of the online pedal parts outlets, circuit specialists (great deal on 10 hammond 1590n boxes and 15% off), tube companies, even amazon(pickup wire).
    Shipping costs are killer. I try to make one order rather than three. Hence my suggestion to build more than one stompbox.

    I started winding when I wanted something better for a MIM strat. I couldn't justify putting that much money into it. All of my guitars have my pickups in them now.

    First time pickup winder? Just use what you have. A reversible power drill or sewing machine will get you there. I built my first winder from scrap wood and a kitchen hand mixer. I still use it. I have tried a hand drill with good results. With the right sewing machine, you'll be stylin'.

    I liken pickups to fifth grade science. That's when we learn about magnets, eddy currents, and coils. Playing with this stuff is just a refresher course. laugh. Having the patience and manual dexterity to deal with wire thinner than hair is "the" make or break skill needed for this endeavor. There are very few variables magnet, wire, shape of coil, metals near the magnet coil structure. Fifth grade stuff if you don't figure in that physicists haven't figured out magnets yet.

    Stompboxes - You will learn more with veroboard than you will with a kit. You mentioned a boost box in the thread. Build these two first, then you will have ideas on modifying a boost box to better suit your needs. (The crunchbox is sort of a modified boost.) You will start to see the similarities as you build and learn. I chose these two pedals because they probably are not like a pedal you have. They are not beginner builds so they fit your skills. And if you don't like them you can give them to someone who will.

    (caution - just like building an amp, the universe will be thrown off should the stompbox work the first time you fire it up.)
     
    Last edited: Jan 17, 2020
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