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Rob Inspired 6G3 - Looking for Feedback:)

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

  1. Snfoilhat

    Snfoilhat Tele-Holic

    Age:
    37
    547
    Apr 8, 2016
    Oakland, CA
    IMG_1861.JPG
    Does this look right to everyone?

    I estimated that at 50% rotation on a log taper pot, that the resistance is 10% of total, but I could be off in my thinking.

    I'm not seeing an advantage over either the Lar-Mar or the Frondelli, but I'm no expert. Looking forward to seeing how that comes out.
     

  2. thesjkexperienc

    thesjkexperienc Tele-Meister

    Age:
    55
    482
    Dec 19, 2008
    Colorado Mountains
    Why are 5e3 kits under $600 and all the 6G3 kits are over $1,000? Weber might have one for less, but I don’t know if it is a true brown deluxe or inspired by....
     

  3. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon

    Hi. I’m not even close to the expert but there’s quite a few significant differences in large parts and then many subtle differences in caps and other smaller parts. So that’s the cost difference right there.

    The 5e3 does not have the tremolo circuit (fewer caps and three less pots etc), only has 2 tubes in preamp section (1x preamp gain section) as opposed to three for the 6g3 (2x preamp gain section).

    Transformers spec a little different too which affects cost.

    Hope that helps.

    Sam
     

  4. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    So were you meaning larmar vs RICH MOD?

    Ok so if the eqn Rt = Rgrid*Rpot/(Rgrid+Rpot) is the right one to use, then I see where you got 153.7. A 250ka gives 117kohm and a 1M gives 180 at max resistance yes? This doesn’t seem to be what the people over in the Metropoulos PPIMV were coming up with though for LARMAR values but these are the values I see for the RICHMOD. The 1.8M to 2.2M safety resistors need to be considered for the LARMAR right? Wwwwwaaaaaaaayyyyyyy over my boots now haha.

    Sam
     

  5. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va
    Both of these MV will effect the nfb levels and make your tone controls less effective as you turn the MV down. They both help a great deal in knocking off a few db's but if you wind them down too far, the tone does suffer. Some folks have implemented adjustable nfb which does help to combat the reduced levels as you turn the MV down.

    I just finished a single channel 6g3 style build and i'm also considering adding a ppimv. While they seem populat for Marshall style circuits, many folks have said that they don't sound so good on the Fender circuits. Could be the lack of cathode follower in these particular circuits that effects the overdriven sound. I'll probably break down and install one just to see if I like it or not though.
     
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  6. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    I would love to hear more about your 6g3, Dan! I actually don’t know a ton about them, like what I might expect compared to my 5f6a (6g3 will break up sooner!)....

    So in running the ppimv resistance numbers:

    LARMAR (boy the Marshall guys love this thing!!!): 250k dual gang, removed grid leaks and the 1.8M safety resistors (the values that rob recommends as opposed to 2.2M that LAR suggests), gets a dimed resistance of 219.5k....ala the ROBLARMAR

    RICHMOD with 1M dual gang and the standard 220k resistors, dimed = 180k.

    RICHMOD with 250k dual gang and std 220k resistors dimed = 117k.

    Why would Metropoulos suggest the 500k dual gang? I’m guessing maybe there’s Consistency in the resistance values throughout the entire sweep of dual gang with lower pot resistance?

    I guess I’m just going to experiment. I plan to go with the 1M RICHMOD since I have that pot, and maybe it won’t sound good at low volumes??????.....unless you guys think I should just go straight to the LARMAR because I do have a 250k dual gang?? I just sort of trust - at this point - the down brownie choice of the RICHMOD, like maybe it sounds better with fender style amps (along lines of what Dan was talking about above).

    Much wiring should get done this weekend!

    My faceplate as of today:

    [​IMG]Untitled by Sam Van, on Flickr
     

  7. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va
    All of the MV's you are considering are fairly similar so if you plan ahead before the build, you should be able to swap a few component values and try all three of them pretty easily. I would suggest to build the amp stock first until you have ironed out all of the details. Don't forget to leave some extra wire length on the OT's secondary wires connecting to pin 3 of the power tubes. You have a 50/50 chance of getting them right on the first go round but you want some extra wire length in case you need to swap them. The amp's DC bias voltage rides on the MV pot on it's way to the grids, so getting the amp working 100% before implementing the MV mod would be a wise choice. Good luck with the build!
     

  8. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va

  9. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Oh my god Dan (rob et al), sorry to be an idiot. I’ve read that page more than once but at the times I did, I didn’t realize RICHMOD was a type of ppimv and thought it was more a part name or something that went with the ppimv....wowza. He even says he used the pec 500k hahaha which I’ve been wondering for the last few days. Well, now I know:) thanks for the heads up.

    I’m going with that! But do I really want to spend the big bucks for the PEC dual gang?

    Thanks again Dan.

    Sam
     

  10. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va
    I have used one as a volume pot in between the first two gain stages of a Princeton style amp and it became a bit scratchy sounding over time. They are sealed so their is no way to clean them like a cheaper pot. They do have an excellent taper though. I did use one in a Larmar ppimv and it has been quiet since I installed it several years back. The great thing about them is the very smooth volume taper that some of the other pots don't seem to have. If you have the money I would definitely use it for the MV position.
     

  11. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    good info dan! I did end up buying one. I also have some vintage dual gangs, one of which appears to be a 500ka....but there was large difference in each gang.....

    ok, I doubt anyone has the patience to look through this but I realized I didn't have the UPRIGHT chassis layout right with respect to pots. I realize that, although the board and overall layout is essentially a flipped image, the pots will not be wired that way (I hope Im right because I just spent mucho hours redrafting!). But here's that layout, with a few of the mods also layed out....


    [​IMG]Print by Sam Van, on Flickr


    and also here's a pic of the vintage capped board (but volume pots are wired wrong and caps/resistors on the pots are also wrong side etc)...wiring these is what got me thinking:).


    [​IMG]Untitled by Sam Van, on Flickr
     

  12. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hello all! I’m looking at transformers and am leaning classictone. They have a model for deluxes (40-18016)

    http://www.classictone.net/40-18016.html


    that has been used successfully in other 6G3 clones so I feel good about that. The standard model has 330v primary. Although those are apparently fine for a 6g3, Down brownie suggests that the vintage specs for a 6g3 had lower plate voltages and thus the brownie uses MERCURY magnetics deluxe PT (FBDP-M) that has lower winding plates of 315v.
    classictone offers an upgraded version of their deluxe PT that has both 330v and optional lower plate windings of 300v.

    http://www.classictone.net/40-18028.html

    Would the 300v work properly, most importantly, and be closer to vintage specs with my modded 6g3? Maybe tonally would be different too?

    Thanks for any thoughts!

    Sam


    And I’m almost all the way wired up woohoo.
     

  13. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    OK went classic tone OT and PT....upgraded PT to have option to use the 300v leads. Meanwhile, here's where Im at. I HOPE you guys will still help me even though I have already wired beyond stock:). But I am still going to leave the PPIMV off for now as has been discussed.

    [​IMG]Untitled by Sam Van, on Flickr
     

  14. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va
    Looking good so far! I used the same PT in a few of my dual 6v6 builds. With the two secondary voltage options and your choice of rectifier tube, you will have several B+ options available. I prefer lower B+ (320-350) because the amp breaks up a bit earlier and feels a bit softer. If you use the amp for gigging, you may like a higher B+ for the extra punch and headroom.
     
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  15. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    It WORKS! And sounds quite nice already and seemingly ultra versatile! Both channels work, Channel jumper works, vox cut didn't seem to work (might be pot because its old??), and tremolo didn't work (but I was thinking thats because I don't have switch yet but I wired in the coax and thus its wired in as OFF????).

    And I got shocked mightily so I guess now Im part of that club (I "think" it was 360v on the rectifier switch because it seemed difficult that I would have touched the 120v on the low side of the switch??? Is this possible?).

    But if you guys don't mind I'd like your thoughts on the following:

    - Last night upon walking quickly through the startup procedure (without variac or light bulb) and then hooking up speaker and power tubes etc it didn't have any sound, or hisses etc at all even though my quick eval of voltages seemed ok. So I assumed it was the way i wired the NFB-impedance selector-speaker jack. But I wasn't just going to jump to that fix yet because I thought the power tubes were red plating AND I couldnt adjust bias (but then again I wasn't trying too hard to understand how to measure bias - slacker!). So I was also worried there were other more serious things to troubleshoot......

    Then this morning I carefully remeasured voltages without power tubes in and got these, which seem sort of OK????:

    [​IMG]6g3_voltages_03092018 by Sam Van, on Flickr

    So then I rewired the NFB and speaker jack WITHOUT impedance selector mini switch, wired the 8 ohm only......installed power tubes and had tone! Then a minor smoke and some poor sound. Turned it off and rewired to 4 ohm secondary BECAUSE THATS WHAT MY CAB IS!!! Hmmm, no smoke and great tone! And it seems like red plating is either much reduced or gone? Does this look like red plating to you guys? This was this morning when it was working great. Last night they were way more red hot.

    [​IMG]IMG_0509 by Sam Van, on Flickr

    So here's how I thought I should wire my impedance selector-NFB-out jack. But I did wonder a) should I have wired it for my 4 ohm speaker even though NFB is set up for 8 ohm? I assumed this would only affect the qualities of the the NFB but was ultimately the right way to wire it?

    I also worried that I did not understand and thus layout correctly where the lead from the 5e3 on the NFB goes/where common goes etc??? Any thoughts on that? Thanks a million for all the help guys! I already love it. Sam

    [​IMG]6g3_ohm_select by Sam Van, on Flickr
     

  16. trouserpress

    trouserpress Tele-Meister

    Age:
    55
    390
    May 4, 2015
    Leipzig
    I hope you can get all issues sorted out, it's quite an interesting build and already looking good. Concerning that shock you really should monitor what your heart(beat) is up to for next couple of days (+weeks!). Don't hesitate to visit a hospital if you feel something abnormal.
    Slow down your building pace - you've got no routine doing this.
    All the best.
     

  17. dan40

    dan40 Tele-Holic

    823
    Aug 19, 2015
    Richmond Va
    Your tubes are definitely redplating and may be ruined if they have been doing this for a bit. Did you include a bias pot in your build? It's an easy mod that is essential with today's wide variance in tubes. Did you install any 1 ohm cathode resistors to help measure bias?
     

  18. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Thanks Dan. Ok yes I have a bias pot but it isn’t doing anything turning it all the way down or up? I forget - since adjusting bias on my bassman long ago - whether it’s more about a sweet spot than it is high or low? I did not install cathode resistors. I’ll look into that.

    What should I expect if the power tubes are “ruined”?

    Sam
     

  19. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hey trouser,

    Well I DIDNT shock myself when I was going fast and only got shocked when I slowed down hahaha... ok i agree about slowing down:). But isn’t the heart concern more relevant had I touched amp with two hands? I don’t think that shock got near my heart and just went into the one arm I was probing amp with?

    Sam
     

  20. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Hey be careful in there!

    With 0vdc on the cathode and no negative grid voltage you are cooking those tubes!!!

    Pull the 6v6's and look for negative voltage at the bias pot. Sweep the pot and record the range. Set it to the most negative value. If you dont have -ve voltage you need to figure out why. This voltage needs to be fed to the grids of the 6v6. Do you have rectifier back up diodes installed?
     

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