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. dan40

    dan40 Tele-Holic

    924
    Aug 19, 2015
    Richmond Va
    Follow D'tar's advice and check for a negative DC voltage at pin 5 of both power tubes. The schematic shows -26 volts so your bias pot should sweep above and below that basic range if it's working correctly. If not, you need to trace back through the bias circuit and see where you are dropping the voltage at. Be sure you have the bias diode orientated correctly and the cap has it's positive to ground.
     

  2. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Are you sure those 1v voltages on pin 5 of 6v6’s in your chart are positive, and not negative?
    You should check first at the wiper of the bias pot, this will be the negative bias applied to grids, assuming you’ve wired that section correctly. And as dan40 said, make sure the bias filter cap is in right, + to gnd.
    The problem with measuring at the grids themselves is that your meter will load the bias through those 220k’s and give an inaccurate reading. (Although it wouldn’t make it go from neg to pos.)
     

  3. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    I'm definitely late to the party on this one. But going back to the PT question. As mentioned the Princeton PT is not up to the Deluxe circuit, it may work for a while but they are pretty faulty even in PR's.
    But what I was gong to say, I have a Princeton Reverb that has been modded a lot over the years. When I got it it had a large PT installed by hacking the chassis. I modded it into a bit of a single channel super reverb type and for years I used it as an outdoor/loud amp with some inherent grit to it.
    A while back I decided to return it to being a PR, as that is a hole in my array of amps I need more now. I returned the filters to the PR values and modded the rest back to a PR, but left the big PT in place for now.
    Now here's the interesting part, with the big PT, but all else returned to PR specs, the amp stays clean far longer/better headroom than a stock PR does. I've gigged quite a bit with 2 of the stock ones in the last 10 years and always found them to get pretty nasty in all but the smallest rooms.
    I guess it just surprised me it did that without bigger filters etc...
     

  4. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    The higher current / lower winding resistance PT is able to charge the filter cap faster and with less voltage drop.
     
    robrob and schmee like this.

  5. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Thank you everybody! I definitely need all the help I can get.

    I will hit it in earnest in next few days but to answer a few questions and make a few comments/questions:

    - bias is adjustable but I just wasn’t seeing any changes when adjusting.

    - I will recheck voltages but those I reported were WITHOUT the 6v6’s installed.

    - the transformers got very very hot, especially the PT.....way hotter than I’ve ever felt on my 5f6a.
     
    D'tar likes this.

  6. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    You need to see approximately -25 to -30 vdc on the input/control grid of the 6v6 pin 5.


    Your pt is pumping all the current it can through the 6v6's, Thats why they are glowing red. Once your bias is under control this should be non issue.
     

  7. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Ok thanks dtar. I forgot to say that I have the tube/solid State mod hooked up.
    So I’m assuming those same diodes work in the same way as the backup diodes???
     

  8. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    If you are tapping the bias from the HT VAC, do it before the recifier diodes

    I cant see in the pics where the tap is connected.

    Assuming your pt does not have a dedicated bias supply.
     

  9. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hey D'Tar (and others) - OK I think you are onto something.....Here's the best blowup I can offer for the Down Brownie, which is much of the inspiration for my amp. But what I think I am seeing is that the lead from the bias connects to pin 3 now that I look harder. I wired mine to pin 2, as its supposed to be on the regular 6G3.

    I've looked over my bias and it seems to be wired correctly and no leads are shorting on underside etc.....

    So do I need the bias to connect to Pin 3 instead?

    Im hesitant to start it up again because I definitely smelled something strange (burning PT?) the last time it was on.....I ordered another PT (without all the extra features), new 6V6's and rectifier tubes in case any of them are struggling....

    DOWN BROWNIE (bias is coming around PT to the rectifier...it is a bit darker yellow than the PT 5v yellow leads)
    [​IMG]DB_tube_ss_blowup-01 by Sam Van, on Flickr

    MY BUILD
    [​IMG]IMG_0511 by Sam Van, on Flickr
     

  10. Fiat_cc

    Fiat_cc Tele-Holic

    Age:
    35
    510
    Oct 8, 2016
    Melbourne, Australia
    You want it to come from whereever you connected your HT secondary to the rectifier socket, which looks like pin 3 or 5 in your build.
     
    Sam VanLaningham likes this.

  11. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Yep... If you remove the power tubes and rectifier tube, put the switch in tube rectification, you can turn on the amp without having high voltage into the circuit. You will have high voltage AC at the PT output red/white wires. This is where you tap for the bias circuit. Move your tap and take voltage readings at the bias pot and at the grids of the power tubes. Set it to the most negative value. Let us know what you have. If it looks good then you can re visit the start up procedure.


    upload_2018-3-13_8-26-35.png
     
    Sam VanLaningham likes this.

  12. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Ok thanks again! I’m going to have to wait til Friday. Can’t wait!

    Sam
     

  13. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Hi all. When I get home this afternoon I’ll get back to it. Whew! But one thing that was happening that I cannot find a solution to:

    My lamp bulbs kept blowing. I didn’t initially have resistors to ground and thought that might be an issue. So then I installed those but they still blew.

    Any thoughts on that?

    Thanks.

    Sam
     

  14. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Woohoo! OK hooked up new PT, double checked all leads. Might have had both 6.3v leads to lamp shorting with each other. The light burns a normal brightness and has not yet burnt out. So that appears solved.

    Went through startup procedure and all voltages checked out, generally.

    Got a negative bias voltage and adjusted it to lowest value I could get = -45v. Much better eh!

    Plugged it in and it sounds awesome!

    Tremolo works great.

    Vox cut works. I replaced pot, which was old and thus suspect.

    Note however that it sounded really good when I was burning it up before. It was quieter with lots of overdrive and I was wondering to myself "why would anyone want a master volume on these cuz the breakup is awesome as is" hehe, now it's sounding more fender clean like (but more bite than my 5f6a) and so I'll shoot to pop the RICH MOD in (I installed it into my 5f6a and it sounded sooooo much better than the simple TW3).

    How do I do a vox cut AND RICHMOD? I'll connect the vox cut to the caps that are going do be separated from the 220k resistors for the RICHMOD if that seems right to you guys.

    Thanks for everything a million times over, Dan, Dtar, RLee, Rob et al.
     

  15. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    VOLTAGES, just in case anything looks suspicious to you guys....
    [​IMG]6g3_VOLTAGES2 by Sam Van, on Flickr
     

  16. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Sam,

    Your plate voltages extremely high!
     

  17. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon

    Dang it! Thought I was there minus finding the source of a nasty buzz....however is it possible the two are related?

    I have a buzz that my instincts tell me is the two black beauty caps that are running the tremolo. I chopsticked one and the frequency of the buzz changed....chopsticking rest of amp produced no change. Switching to solid state rectifier also increases buzz. At one point the buzz was much louder without a cord plugged in. But now it seems to have equiilibrated cord or no.

    So I plan to replace those caps. If they’re leaky could that allow for excess voltage sneaking through to the plates? Again, way beyond my knowledge base. I’d love any other thoughts.

    Today, I got close to finishing the head cab. I love it! The tolex and grill cloth are far from perfect but I view it as a prototype:). And I also put my new guitar im building but have been unmotivated to buff and finish up..... maybe I’m about there.

    Sam

    [​IMG]Untitled by Sam Van, on Flickr

    [​IMG]Untitled by Sam Van, on Flickr

    [​IMG]Untitled by Sam Van, on Flickr

    [​IMG]Untitled by Sam Van, on Flickr
     
    robrob likes this.

  18. cap47

    cap47 Tele-Holic Silver Supporter

    527
    Jul 27, 2014
    bushnell, fl
    I really like that, great job Sam! Welcome to the recent 6G3 Build Club! LOL
     
    Sam VanLaningham likes this.

  19. Sam VanLaningham

    Sam VanLaningham TDPRI Member

    90
    Jan 6, 2018
    Bend Oregon
    Thanks Cap! Hope to get it right though. Indeed Dtar aint kidding. My plate voltages are insanely high, supposed to be max 375v ish????

    My instincts were NOT dialed in. I replaced the black beauties, maybe a little decrease in buzz but no real change???? Then replaced the vintage .068uf lead channel bypass and its resistor.....and an oddball beat up looking cap that was on the lead channels tone pot. No change except a brighter noise after these changes.

    The new sozo 0.068uf bypass cap is actually a bit microphonic when I hit it. But that ma have been the case with the old one too. So i resoldered connections there. Also swapped first preamp tube which didn't change anything. But all my 12ax7/7025's are old and while it seemed they weren't causing probs in the bassman, maybe i need to get some new 12ax7's to help test?

    Sam
     

  20. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Look closely at your power dropping string of resistors. Recheck those voltages to confirm they are indeed that high. This would be my priority before swapping in any new parts, or chasing humm/noise. Some new pictures may help also.
     

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