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Filament buss question

Discussion in 'Shock Brother's DIY Amps' started by moosie, Nov 23, 2017.

  1. Phrygian77

    Phrygian77 Tele-Holic

    758
    Apr 30, 2016
    Crawfordville, FL
    Nice work so far, guys. If you get this thing figured out, I may just have to build one. But, instead of dealing with that cramped nightmare of a kit, I think I'd want to do my own layout and board to fit into a PR chassis and head cabinet.
     
    moosie and Snfoilhat like this.

  2. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Thanks. Yes, that's what I was thinking, too. The idea of the outboard tank cab with the cool surprise inside is neat, but a pain to build.

    I think whatever further tweaking we do, it'll be minimal, and I suspect it's going to be a matter of individual component values. Meaning, you'll still have to dial yours in, once you build it. So, don't let me hold you up. Get started! :D I already can't wait to build another.
     

  3. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Yep. Sounds good.

    Are you saying let's leave the 100k loads in place for now, and tweak the cathode first?

    Incidentally, I was searching the web for an old link to the rev3 schematic, thinking that even if it was defunct, I might be able to pull it out of archive.org's Wayback Machine, like I did with Gehring's build page. I didn't find it, but I may have found Mr. Gehring himself. He seems active on The Gear Page. I just PM'ed him with our situation.
     

  4. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Jeff replies:

    As you suspect, the tremolo performance is a see-saw balance of the amount of LFO drive versus the bias point of the V4 modulator stage. Have you tried increasing the LFO drive to V4 by reducing the R37 4.7M series resistor on the oscillator output, feeding the intensity pot?

    R16 was a 150 ohm resistor shunting the RCA jack feeding the reverb tank input. It is not necessary; the original intent was to prevent damage if someone ran the unit with no reverb tank plugged in.




    I'm confused over the difference between increasing LFO drive by reducing R37, and what we just did by raising the top end of the intensity pot.
     

  5. Phrygian77

    Phrygian77 Tele-Holic

    758
    Apr 30, 2016
    Crawfordville, FL
    Can't wait to build another, huh? Seems like the DirecTV commercial. You know, uncommon pleasures like banging your head, paper cuts, camping in poison ivy, etc. :D

    Well, I've got a Super Lead chassis sitting here that I'm planning to build a 6V6 1987 in first. But, a 6G15 has been on my short list, to use with my Blackface Bassman build, and this thread has me intrigued about doing it with the harmonic tremolo. Maybe this year sometime.
     
    moosie likes this.

  6. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    His method would raise the amount of drive available while keeping the 0 to 10 sweep of the pot - basically, 10 gets stronger while 0 stays the same. Our method has effectively made the range 2 to 12. It's basically six of one, half dozen of the other at this point, but his method is a little more elegant in that the existing solder points are already used, vs adding a new component. Feel free to experiment with lowering his specified resistor in conjunction with adjusting what you added to the pot earlier - you might find a balance you really like.

    The 150r makes total sense. I've seen 270r resistors strapped across output jacks for the same purpose.

    And it's really cool that you found the designer online. I generally avoid that forum, as it can get really contentious and myths & snake oil flow freely at times. I like the laid back, friendly atmosphere here a lot.
     
    King Fan likes this.

  7. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    You know, I'm rethinking this kit myself just for the cramped aspect of it. Now that we have a handle on it, it's really not that daunting.

    I wanna build a 6G12-A Concert instead. :)
     

  8. Phrygian77

    Phrygian77 Tele-Holic

    758
    Apr 30, 2016
    Crawfordville, FL
    I've seriously always wanted one. I've always though thought of it as one of the ultimate Fender amps. But, that's WAY too much amp for me. My Bassman combo with a single 100dB 12" is loud as hell as is. I don't need what's basically the same the same power section with 4x10s. Tapped treble pots, who even has those now days anyway?

    Building the ReVibe in a Princeton Reverb sized head might be a little big, but it would at least be a comfortable build, and the tank would fit perfectly in a bag in the bottom. Seems like a perfect plan to me.
     

  9. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Our method seems fine, then. In fact, for testing, why don't I use a 6M resistor, and make it essentially a 6-16 range on the depth pot. I don't have to use it all, but in conjunction with the cathode trimmer, it would be the equivalent of having a second trimmer. Would I need to avoid diming it, lest we redplate the triodes?


    I only hang at TDPRI, though I do sometimes browse or even post a bit on MLP, UMGF or AGF. TGP threads tend to move too quickly. I do like buying and selling over there, though. I've done over 50 transactions, and not a single issue. Nice folks.

    I gave Jeff the link to this thread, hoping he'd join in, but I can see why it might not be as exciting for him. It's work he did over a decade ago, after all.



    Oh, I said the unit got noisy? I was mistaken. I have an amp A/B/Y switch with a ground lift. It was lifted. Flicked the switch and it's still DEAD silent. Whew.
     

  10. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    How about 3.3M or 4.7M, and reevaluate. Or even better, get that trimmer installed and dial in V4. The best way to do this is methodically, IMO. One change, test, another change, test, etc. It avoids the problem of making a major shift in the circuit, and it suddenly doesn't work at all - especially since we're doing this by internet, where I can't evaluate on the fly and keep us out of the weeds. Like he said, it's a delicate see-saw.

    I think the triodes should be fine as long as we don't get crazy with it. This circuit works by pushing the tubes into cutoff (no current flow), but it could be possible to drive it too hard at the other end of a large LFO cycle and start to push things a bit too hard. We'd probably become grid current limited first, and that could have some strange side effects on the sound.
     

  11. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I agree with your point. I think we're not quite on the same page here.

    I meant to set up a testbed with two trimmers. One, the 2k on the cathode, adjusting from 4k7 to 6k7. And the other made by changing the range on the depth pot to give us plenty of room to adjust. For example, replacing the 2M resistor with a 6M would give us a pot equivalent to 6-16 on the original scale. Setting it at 6 would be the same as diming it now, but I would also have room to tweak. Just like the cathode trimmer.

    Then, when optimal values are identified for each component, remove both and install the correct values permanently.

    That's what I was thinking. But, I can see how this might make it more difficult for you to assist remotely.

    How about this:

    Install the cathode trimmer, and leave the 2M in place for now. Run through the range of settings.

    Then, if it's not immediately awesome, swap the 2M for a 3.3, and run through the trimmer once again. Rinse repeat.

    I'm guessing for you to assist, you'll want both sound clips, and V4 cathode, grid, and plate measurements, in real time with the scope.

    How does that sound? The part arrives tomorrow.
     
    clintj likes this.

  12. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I still have the 100k plate resistors installed. Would you like me to revert that to Gehring's v4 spec before we test?
     

  13. Phrygian77

    Phrygian77 Tele-Holic

    758
    Apr 30, 2016
    Crawfordville, FL
    I still haven't seen a legit theory as to why those plate load resistors were changed to begin with. Hell, I'm still wondering why did he did a split plate load on the second gain stage of the reverb.
     

  14. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Right, me too.
     

  15. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    I think the goal here is for you to be most satisfied with the finished sound. You're getting some pretty good results here, and we now know the system is working and why it wasn't before. So, in that spirit, your ears are your best piece of test gear unless something weird happens. I do the same on final tweaking and voicing.

    With the V4 plate loads, I think it sounded a little better after you swapped to 100k, personally. You can certainly swap them back to 220k and give a listen if you like. Whichever you elect to use, stick with it from here forward for tweaking.

    I like that on the 2M idea. Sounds like a solid plan to me. We may also find a sweet spot with the cathode trimmer that makes the 2M obsolete, too.
     

  16. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I'll leave the 100k in place.

    It it interesting that when Leo wrote that patent, he was thinking it would take a 15k cathode resistor.
     

  17. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Hadn't heard from you in a few days. Any progress or good news?
     

  18. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Standing by, Houston...
     

  19. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Sorry for the delay. First snow delayed the part, and then life delayed my working on it. Hoping to have something tonight or tomorrow.
     

  20. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Don't rush. Despite the way we all act here, life comes first!!!
     

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