Blackface Twin Reverb Build (my first from scratch!)

Discussion in 'Shock Brother's DIY Amps' started by JKube, May 24, 2017.

  1. robrob

    robrob Poster Extraordinaire Ad Free Member

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    That is a sexy amp.

    The vibrato tick is usually caused by interaction between wires--many times with wires run under the board. It can be fixed with a cap.

    Try another tube in the reverb driver and then reverb recovery sockets. A cap can also be added (already there in silverface amps) to quiet the reverb circuit.

    Details here: https://robrobinette.com/AB763_Modifications.htm
     
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  2. JKube

    JKube TDPRI Member

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    Thanks Rob! The vibrato tick is so faint, you barely know it's there. I'm just being hyper-critical because I still can't believe how well the amp is sounding right away. I might throw a 12AU7 in the reverb driver slot to see if I can gain some pot range and loosen up the sound a bit. It's basically unusable past 5. Got some travel for work this week, so it'll have to wait. I ran the TR and the DRRI in stereo last night, I can officially sell everything else I own....
     
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  3. JKube

    JKube TDPRI Member

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    Here's the promised Hi-res finished product. Hope these help folks looking for answers like I was a week ago.

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  4. JKube

    JKube TDPRI Member

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  5. JKube

    JKube TDPRI Member

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  6. boredguy6060

    boredguy6060 Friend of Leo's

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    Very nice indeed!
     
  7. King Fan

    King Fan Friend of Leo's

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    I don't know about that jewel lamp!!! :)

    Seriously, this thread is up for awards in so many categories.

    1. Best build pics
    2. Most useful build pics
    3. Most humble and gracious OP
    4. Most talented humble OP
    5. Most ambitious build ... that succeeded
    6. Prettiest dang Twin Reverb in history
     
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  8. RifleSlinger

    RifleSlinger Tele-Meister

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    7. Most inspirational: I know nothing, but this has made me want to learn all I can. I will study hard and practice diligently for a year and, if I feel ready, give this a go.
     
  9. JKube

    JKube TDPRI Member

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    I had blue and red, decided to try something different! I think I'm with you though, the red might be going in soon.

    I appreciate the kind words. It was probably more ambitious than I realized, but I guess ignorance is bliss! I will say, no matter how complicated the circuit may seem, if you approach it like several small circuits, it's much less overwhelming. It's the "how do you eat an elephant.... one bite at a time" approach. If I can do it, anyone can do it! I know that I spent a lot of time looking at the photos that you and Rob, Clint, and the rest of the folks here posted for reference. A schematic is great, but a good visual of which wire goes where, how to suspend cathode resistors, how to fly wires, etc would have been nice in a good resolution. Hopefully the different phases throughout the thread plus the final shots fill that gap for others.

    Now I'm gonna go swap that jewel....
     
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  10. JKube

    JKube TDPRI Member

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    The best part, I feel 1000% smarter on how this box of resistors and caps actually molds sound than I did 30 days ago. The sweet amp is a bonus!
     
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  11. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    I am very impressed @JKube! You did a great job.

    I am in the midst of wading in on my first big amp repair foray and you have been an inspiration to me as well! I like your description of breaking it down into smaller circuits to digest it better. That's what I've been doing as well. I'm not smart enough to view the whole picture yet! LOL
     
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  12. moosie

    moosie Doctor of Teleocity Ad Free Member

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    I like the blue jewel!

    @JKube, before we all leave, and go about our daily lives, with a new persistent itch.... and in the interest of best-thread-ever documentation...

    What parts, if any, did you use that were not in the Mojo kit?
     
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  13. robrob

    robrob Poster Extraordinaire Ad Free Member

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    It takes guts to to post high-res pictures of one's handiwork. Congrats on building a much-nicer-than-factory Twin Reverb. The world is a better place today because of that amp you created. Bravo!
     
  14. JKube

    JKube TDPRI Member

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    I used the small parts kit, the mojotone PT, OT, reverb tranny, choke, and chassis (ordered separately). I sourced parts for the ground bus and mounting bolts from Ace Hardware. The lockwire pliers for ease of twisting came from Harbor Freight. Tubes are a JJ's set from Eurotubes. I ordered $30 worth of extra yellow, green, red, black, and bare 20ga wire from hoffman (basically doubled what mojo provided so I could do more wiring outside/leave more slack before the boards went in. Only deviation from the original Fender schematic is the 10Kr bias resistor to gain usable range on the pot.

    Speaking of.... I have a ton of extra orange drops and 1/4w resistors that I couldn't use. Anyone building an amp that could use them?
     
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  15. JKube

    JKube TDPRI Member

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    Some of the solder joints, not my prettiest work, but this is the first time I've ever had to cram three components and three wires into a single eyelet!

    I'm gonna be on a plane later, I'll probably type up a summary of all of the lessons learned through the thread and post them up in one post.
     
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  16. JKube

    JKube TDPRI Member

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    Best way to learn is to do (for me anyway). Amps are scary and dangerous, but not really during a build. The entire process is power off until you decide you are comfortable enough with you product to apply power. Even then, light bulb limiters and variacs mitigate a great deal of the risk in damage. Dangerous still, so I would focus your studies on safe practices and general electronic principals. With a good head on your shoulders, patience, and an enjoyment for the journey more than the result, you could get through a build like this no problem. Schematics and layouts make it a color-by-number really. It's a matter of being able to take the time to review, review, and re-review, and as someone said before, spend 25% of your time assembling, and 75% or your time reviewing, scrutinizing, and most importantly, before and after board installations, verifying continuity where it needs to be and just as important, no continuity where it shouldn't be (power nodes to ground, etc.). With all of that behind me, I was still nervous about applying power, but do your due diligence and take care of the build, it will usually retain all of its smoke!
     
  17. RifleSlinger

    RifleSlinger Tele-Meister

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    Thanks for the words of wisdom.
     
  18. Andy B

    Andy B Friend of Leo's Silver Supporter

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    Way cool!
     
  19. sds1

    sds1 Tele-Afflicted

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    Hi, referencing this build heavily right now -- thanks.

    Question about your grounding -- are there 2 white wires coming from the cap board and curly-fried around the ABCD wires? One goes to preamp ground bus and the other to a chassis lug located near the top-left of the board?

    I think that should be how it's run but I can't see the white wire(s) or that lug real clear enough to know for sure. Thanks in advance, great job. :)
     
  20. JKube

    JKube TDPRI Member

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    Close. That's just a single wire, a makeshift shield for the high voltage B+. It is only grounded on one end, at the preamp bus. There are conflicting schools of thought on this, but providing a ground reference on both ends of a bus can potentially cause ground loop issues. My preamp bus is grounded at the input jack (and the screwed down copper lug technically, but that is before any of the preamp grounds), and is heatshrinked and isolated on the other end. Tieing the curly white wire to ground would ground the far end of the bus (which I decided I didn't want to do) so where you think it is connected to a lug, it's actually just heat shinked and tucked under the wires. For what it's worth, I alligator clipped a ground to that end and saw no difference in noise or signal. I think you're safe either way.
     
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