Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups darrenriley.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Rob Inspired 6G3 - Looking for Feedback:)

Discussion in 'Shock Brother's DIY Amps' started by Sam VanLaningham, Feb 9, 2018.

  1. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Ok thanks a trillion for the help. I guess I made a lot of assumptions about the DB 's PPIMV and then because you demonstrated that the frondelli is the most transparent, I liked that idea myself.

    Here's a blowup of the DB and then my depiction of the layout. I see no failsafe resistors or 1.5k resistors connected to the path. But then I wonder if the DB uses a dual gang with higher resistance or something? I am swimming in the deep end!

    Sam

    [​IMG]downbrown_ppimv1-01 by Sam Van, on Flickr
     
    Last edited: Feb 18, 2018

  2. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    Canada
    Eeeeeeeeeeeeeeeeee..........


    feedback.
     

  3. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    That does look like a dual-gang master volume pot. Since there are no safety resistors I would assume that's a Frondelli. I assume the 220k grid leaks have been clipped and not removed.

    I was mistaken about having to separate the 220k grid leak resistors because the dual-gang pot replaces them so they can be left out.

    The blue wire running from the 220k grid leaks to the bias circuit would be your "intensity" wire.
    [​IMG]
     
    Sam VanLaningham likes this.

  4. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hey Fred (can't be another Printer2 eh!). I was looking for both positive and negative feedback, so thanks! Hope youre well.

    Sam
     

  5. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Thanks for digging in with me, Rob! Glad I'm not totally out to lunch too, interpreting the down brownie circuitry relative to your mod layouts for the bassman et al.

    So do you still think I should wait on the vox cut?

    Sam
     

  6. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    I would wait to wire up the pot until I got the amp running and the master volume worked as it should.
     
    Sam VanLaningham likes this.

  7. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Ok so I’m reworking my faceplate and waiting for the terminal lugs.

    But I thought I’d show the other angle of the DB power tube grid leaks to show they don’t seem clipped. So I am guessing there’s just some extra or redundant resistance on the path??? Again, swimming in the deep end. Meanwhile, I’ll keep re reading about the flow of electrons and the rate of flow!

    Sam

    [​IMG]IMG_0358 by Sam Van, on Flickr
     

  8. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    It does look like the grid leak resistors are in play so I don't know what master volume that is.
     
    Sam VanLaningham likes this.

  9. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    So if I’m reading correctly, additional resistance in power tube grid leaks means a couple things:

    - they serve as high pass filters when combined with a coupling cap (which is the case here it appears) so some amount of lower frequencies get filtered out, and specifically the higher the resistance the more the lows get filtered out, if I understand what I’m reading correctly?

    - in some configs they are voltage dividers?? and affect gain. It appears that higher grid leak resistance means higher gain????

    I’m mostly processing info out loud here.

    Thanks for listening hehe:).

    Sam
     

  10. Snfoilhat

    Snfoilhat Tele-Holic

    Age:
    37
    547
    Apr 8, 2016
    Oakland, CA
    Maybe Down Brownie parallels the grid leaks on the board with the 'grid leaks' in the dual gang pot?

    220K grid leak paralleled with 250K in the pot puts you at 117K, which is not Fender standard but still fine for fixed bias, right? And a 500K dual gang pot would make the total grid leak resistance closer to Fender, but I can't predict if that would make the taper of the pot better or worse. I know my last amp with the Frondelli PPIMV doesn't have the best taper, for all that it works very well in other respects.
     
    Last edited: Feb 21, 2018
    Sam VanLaningham likes this.

  11. JuneauMike

    JuneauMike Friend of Leo's

    May 5, 2015
    Alaska
    Sam,
    I would spend considerable time sourcing the PT and be very reluctant to take Mojotone's recommendation. I am card-carrying member of the Mojotone Newbie Victim's Club, buying a 5F11 transformer based on their recommendation and absolutely nothing else. I was incredibly dumb back then and I'd say I'm about 10 percent smarter now, ha. As a newbie, I'd suggest you arrive at the ballpark B+ that you want and then get the help of knowledgeable builders on sourcing the PT that gets you there.

    If you lurk around here for a while you'll find numerous stories of folks fighting higher than anticipated voltages from Mojotone's "recommended" transformers. Its expanded our knowledge, but the headaches are no fun. The story is usually the same; good transformers, wrong amp. Not Mojotone's fault, and they are a good company overall. Its our fault for not knowing exactly what we're looking for.

    Doug Hoffman is a really nice guy and you can email him for some guidance. He's also great to buy from. Once all your questions are answered here and elsewhere, then buy the iron. FWIW.
     
    Last edited: Feb 21, 2018

  12. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Thanks mike! Yeah I’m passing on mojotone. I think I’ll go with classictones tweed deluxe that has the optional lowered 330v leads and/or (building two of these) the mercury mag PT for the 6g3 that is used in the down brownie.

    And yeah Hoffman amps is where I bought my transformers for my bassman. I’m a fan. However I tried to email him recently and the email bounced. So if you know of a working email, could you give it to me if you have it?

    Sam
     

  13. JuneauMike

    JuneauMike Friend of Leo's

    May 5, 2015
    Alaska
    I want to be clear, Mojotone transformers are good iron (I think they are Heyboer) its just that their recommended pairings seem to be questionable if you are aiming at a more brown vintage sound.

    Doug Hoffman
     
    Last edited: Feb 21, 2018
    Sam VanLaningham likes this.

  14. dan40

    dan40 Tele-Holic

    824
    Aug 19, 2015
    Richmond Va
    Check out the master volume shown at the bottom of this page from Valvestorm. It was called a "Rich Mod MV" over at the Metroamp forum and it is the type that George Metropoulos uses on his newer amps. It may be the same as the one in your pic above...http://valvestorm.com/Amp Mods/PPIMV#Installation
     
    Sam VanLaningham and Snfoilhat like this.

  15. dan40

    dan40 Tele-Holic

    824
    Aug 19, 2015
    Richmond Va
    It does require breaking the connection between the .022uf pi caps and the 220k's by adding two more turrets. You can also hang the caps from the pot as shown in the installation pic if you don't want to add the extra turrets.
     
    Sam VanLaningham likes this.

  16. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Nice work Dan! Thanks so much. This rich mod is indeed what is in the down brownie as far as I can tell = the wiring looks identical. My world expands........

    It calls for a 500 ka dual gang (I’d have to order one).....however in reading about this rich mod, it does appear that some prefer a 250 ka (I have one!) because at lower volumes, the resistance remains closer to this value as opposed to the 500 or 1mohm......

    Additionally and possibly serendipitously, one guy discussing his favoritism for the 250k dual gang also says it pairs well with “the cut mod installed on the PI”....seems like that describes the vox cut, right!?!?


    I’m not seeing any first hand experience comparing the rich mod to the frondelli. But quite a bit of back and forth exists comparing the rich mod and the lar-mar....appears there’s no clear cut favorite.

    As you guys know, I’m way over my boots here (and really loving every second of it!). But I guess I’ll just go for it with the way the DB is wired to start
    = rich mod, unless there’s a good argument to try to frondelli et al.

    Thanks again everyone for helping me so much.

    Sam
     

  17. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hey so what you described here is essentially the rich mod? And you too are saying a dual gang 250k would work just fine, though a bit different then fender?

    Good stuff, tinfoil!

    Sam
     

  18. Snfoilhat

    Snfoilhat Tele-Holic

    Age:
    37
    547
    Apr 8, 2016
    Oakland, CA
    I don't think so. I'm not sure, but it looks like the master volume pot is in series with the grid leaks. I dislike trying to talk about a circuit without seeing a schematic. Not to be a complainer, but layouts and photos of wiring are just harder to read. They are on the other hand easier to copy, and so there are two camps.

    Anyhow, my understanding of the story is that the 6V6GT data sheets from way back when all give a maximum grid resistance of 500K for cathode bias and 100K for fixed bias, but Fenders have always used 220K grid leak resistors in fixed bias 6V6GT amps, showing there is some latitude in what the tubes will tolerate. This PPIMV from valvestorm (and the Down Brownie if it in fact uses it) seems to violate that limit even further (500K+220K at full rotation), but as I said I am not sure.
     

  19. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Right? When I first started hanging out here, I was puzzled by the constant use of layouts for situations where a circuit was being discussed... things you can see at a glance on a schematic take several minutes to trace out on a layout or photo. Layouts show parts location, orientation, and relative size, and some hints as to wire locations, but no sense of what the circuit does.

    Then I realized that one reason for this is because nearly all the layouts for tube amps don’t have component numbering (R1, C2, etc) that match numbering on the schematic, which is the industry standard (except for vintage amps it seems). If that was available, I think we might see more folks benefiting from using both schematics and layouts together, as intended... best of both perspectives.

    It’s much easier and less error prone to use the layout just for locating parts (and some wire routing hints of course), and use the schematic to verify the actual component wiring (pin 1 of V3 to + side of C2, etc), then use a marker to highlight that line on the schematic as done. I think there would be fewer cases of missed connections on a build; it’s tough to see that you missed a ground on a layout, but obvious on a marked up schematic.

    And as you noted, for discussing circuit operation a layout is really cumbersome.
     

  20. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    I wanna get there my bruthas! And you’re right, rlee, I saw a vox schematic with component numbering and that helped. I remember almost nothing from college physics classes....I was just trying to get by (“and keep my sideburns too”)....so I just plain ol suck at having intuitive circuit understanding.

    Ok I’m approx 30 pages into a 119 page THREAD on PPIMV over on The Metropoulos forum....it’s fascinating because it seems to be where the LAR-MAR was born (or at least where Larry and mark came together to create their version of it.....many came before them as well). But the thread is supposedly going to morph into a rich mod discussion. I’m still learning that way but I’m waiting to learn if the rich mod affects NFB like LARMAR does....
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.