Deluxe Reverb AB763 Build

Discussion in 'Shock Brother's DIY Amps' started by MasterEvan07, Mar 15, 2019.

  1. MasterEvan07

    MasterEvan07 Tele-Meister

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    This build could take a while to complete, but I'm going to finish it and I would love feedback and guidance along the way - this place has some of the best of that.

    Here's what I started with:

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    After some chassis "TLC" -

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    Circuit -

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    I don't yet know if the transformers or blue molded caps are any good, and I don't know if there's anything else worth salvaging from the circuit board, but I'm hoping hanging out here will clarify some of those quandaries.

    Next step is probably a Mojo small parts kit and Heyboer OT. Recommendations and suggestions welcome.

    I've been reading @robrob's site with intentionality for the first time in years and it's really sparked my desire to get back into this but to actually understand it this time. I've tried and fallen off the wagon a few times in the past.
     
    Last edited: Mar 15, 2019
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  2. schmee

    schmee Poster Extraordinaire Silver Supporter

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    Cool. Submerged? The tranny's may still work. My bet is the blues are ok.
    I would go with only Switchcraft on jacks.
    CTS pots in the correct values you can find.
    I rebuilt a '49 RCA art deco PA amp once that had been sitting outside in the rain according to the seller. Full of debris etc. Amazingly, the trannys and pots were good. All the paper caps had come apart of course.
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    Last edited: Mar 15, 2019
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  3. theprofessor

    theprofessor Friend of Leo's

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    Magnificent. I love restoration threads like these. I look forward to seeing what you do. I have a vintage Deluxe Reverb, so they're near and dear to my heart. Yours looks to be a 1967 chassis?
     
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  4. MasterEvan07

    MasterEvan07 Tele-Meister

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    Yep, transformer codes are mostly from '66 it looks like, but the chassis is '67.
     
  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    [​IMG]
     
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  6. MasterEvan07

    MasterEvan07 Tele-Meister

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    So I'm looking at both Hoffman and Mojo for kits. Any preferences for either? Hoffman has all metal film resistors and ceramic sockets. I'm not necessarily against them but seems like most people don't like to use MF in the audio path and I like Belton sockets. Also they're just 1/2W and Rob's mentioned 1W will be quieter on his site, and I want it quiet.

    If I had plenty of disposable income I'd try lots of things, but I want to do this right the first time and keep learning and growing from there.
     
  7. theprofessor

    theprofessor Friend of Leo's

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    I have used Mojo kits and parts, and you can't go wrong with them. I've also built a Princeton Reverb with Doug Hoffman's parts and layout, and it was magnificent. I would have no hesitation about using Hoffman's parts and layout. It will be quiet. The only thing I don't like about Hoffman's parts is that the CTS pots he sources have a vinyl shaft. I always order the CTS pots with brass shafts that can only be had from Mojotone.

    I have never built an amp with only metal film resistors. I tend to be partial to carbon comps, which are noisier. You could use metal film most everywhere but substitute carbon comp where there will be the most distortion.

    In other words, you can't go wrong. The Princeton Reverb I built on Hoffman's layout and with his parts is one of the best amps I've heard, and it was dead quiet. And Mojotone has never failed me, either.
     
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  8. clintj

    clintj Friend of Leo's

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    AB763 amps are fairly low gain, so it's not going to be that bad even with all CC. My SR is pretty darn quiet. They're also period correct for the amp. Another downside, however, is they're unstable over time and can drift a lot in some cases. New resistors are also shorter than NOS and may just barely reach the eyelets in some spots. You can cut the most noise by replacing just the input jack resistors and V1/V2 plate loads with 1W metal film. You'll need four 100k, four 68k, and two 1M to do this.

    There's nothing wrong with going all metal film, either. Any non-linearity CC adds is dwarfed by what the tubes add, and these are reliable, stable, and quiet. You won't be in there later replacing crackling resistors later as it ages.

    There's a third option, but it'll take some work to make sure you order all the right values. 1W carbon film. Some of the "mojo" people claim from CC, about 1/10 the noise, and long term stability.

    Sent from my Pixel 2 using Tapatalk
     
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  9. theprofessor

    theprofessor Friend of Leo's

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    You probably already know this, but clintj is one of the experts around here; I'm not. So... what he said.

    His comments reminded me of a couple of things: I have always used metal film on the inputs, but in general, I can't stand the flimsy and short leads on metal film resistors. They're very difficult to manipulate. I much prefer the thicker leads on the carbon comps, and I really like the old Allen Bradley carbon comps with very thick copper leads. The only downside to those is they take up more space in an eyelet.

    But if Hoffman has a special layout that he designed for the amp you're building (he does for the Princeton Reverb), he'll have taken lead-length into account.
     
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  10. D'tar

    D'tar Friend of Leo's

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    Doug Hoffman has 1/2w cc resistors and belton sockets. He makes it very easy to modify the parts list so you get what you want.
     
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  11. MasterEvan07

    MasterEvan07 Tele-Meister

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    Thanks for the thoughts, friends!

    I think the 1W substitution approach is what I'm going to try for. Maybe some Takman or something from CE Dist.
     
  12. clintj

    clintj Friend of Leo's

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    Check out Mouser. There's a little bit of a learning curve to drill down using their filter options, but their inventory is huge and their prices are good.

    Sent from my Pixel 2 using Tapatalk
     
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  13. sds1

    sds1 Tele-Afflicted

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  14. MasterEvan07

    MasterEvan07 Tele-Meister

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    Parts ordered! A little here and a little there but worked out without shipping costs being prohibitive or undoing any savings. I'll update as parts arrive!
     
  15. MasterEvan07

    MasterEvan07 Tele-Meister

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    [​IMG]

    The original panel was weathered and bent a bit, but a car restoration buddy of mine took it, cleaned it up and revitalized the front. It's looking great and just waiting to be installed on its original chassis for another 50 years :)
     
  16. MasterEvan07

    MasterEvan07 Tele-Meister

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    Got the first round of parts in and I'm sorting what I overlooked working between a couple resources. So far mostly good, just a couple little thing I missed.

    I'm looking at StewMac's build docs for their thoroughness but using @robrob's layout as a guide.

    -Hoffman bypass caps were all 22uf @ 50V - is that difference negligible or consequential?
    -Rob's layout uses mostly linear pots, though the original Fender schematic and the StewMac docs are all audio (or reverse audio) except the 100KL...?
    -If I use a .0022uf instead of the .0033uf for the V4A coupling cap will that big a problem?
     
  17. Faceman

    Faceman Tele-Meister

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    Love it! I just got a 1963 Showman done that was in similar shape. It was fun bringing it back to life. Here is a link...
     
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  18. clintj

    clintj Friend of Leo's

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    Bypass caps: those are equivalent. All good there.

    Pots: personally, I'd go with the Fender specified taper, especially on the volume pots.

    V4A cap: that'll limit low end more than stock on the wet reverb signal, may even make it seem too bright. I'd have to get out the calculator and see where the corner frequency actually lies. Again, I'd go with the original values.

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  19. MasterEvan07

    MasterEvan07 Tele-Meister

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    Agreed.

    I think I can reuse the remaining ceramic disc caps from the original board for anything I'm missing. I opted for the audio taper and the 1W CF resistors across the board.

    I could only find 2M and 3M CF for the trem jump start and reverb mix resistors. I'm not sure if that's within acceptable margins. More than asking "is this ok?" I want to learn how to comprehend the application and ramifications of changes - minute or major.

    I've got one of the Blencowe books, which I'll be breaking into sooner than later, and I'm poring over Rob's stuff, so I'm really grateful to the willing and gracious guidance of all the more experienced fellows here helping further my knowledge and education. Thanks a ton!
     
  20. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The only linear pots in my layout are the reverb and bias just like Fender. Log = Audio taper.
     
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