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6G2 build begun

Discussion in 'Shock Brother's DIY Amps' started by King Fan, Oct 21, 2017.

  1. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Gentlemen, a new titan walks the heavens.

    No, the creek did not rise, exactly. The amp had passed the Rob and Sluckey in-build tests, and proceeded to pass safety ground, ohmmeter, and continuity testing, plenty-o-bias check, no-tube tests, rectifier-only tests, and then heater glow and voltage tests.

    Plugged in an old speaker (sitting in a box on the bench) and a guitar -- woohoo -- sound. Guitar sound, even. Since things looked good, I swapped out my 'R&D' JJ big tubes and beater minis and stuck in NOS.

    This was all with the NFB lifted, because easier. So of course when I clipped in the NFB, there was a faint howl -- like a toddler not getting a candy bar on the other side of the store -- as the amp warmed up. No deafening squeal, but present even with the volume on zero. So I switched the OT secondaries and bingo, clear, quiet, pretty sound.

    Voltages looked pretty good, mostly. But i knew that getting my bias set would change B+ and might take some iteration.

    Then it started to rain in the headwaters of that darn creek. As noted, I'd used Doug Hoffman's 'Princeton bias pot' setup. But I couldn't start to get the bias hot enough -- got as high as 14 or 17 mV when I wanted 22 to 25 or more. I'd used a 30k resistor to ground off the bias pot, using the original value from the bias board just like I did on my PR. Hmm, let's swap in 27k, a 'universal' Princeton value. Still not getting there, but better. Luckily, I'd been OCD enough to also order a 24k, and with that in there I have 'just enough' range to get in the 60-70% dispersion range.

    B+ is around 333, power tube plate-cathode voltage is 328, and I get 22 and 25mV on my 1-ohm resistors.

    So I put the real speaker in the real cab on the floor and plugged in to the chassis using a speaker extension cable... In the basement, heaven. Sustain and grit and chime and -- oh, nvm, this is a family-friendly website.

    But when I stuck it all together and got it upstairs -- total silence. Red lamp, no smells, no sparks, but no sound. How could putting the amp in the cab kill it?

    But I had one idea. Only one. Back in the basement I plugged in the speaker extension cable, which has a big, fat, full-length Switchcraft plug. The speaker in the amp has one of those great old-style right-angle plastic-cover Fender 'F' plugs. And when you lifted the cab up on the bench, and plugged that in directly, and looked at the shunt jack, it wasn't bent quite far enough to separate from the tip jack.. Two seconds with a bladed screwdriver, and bingo. Luckily for me I've seen this once before; in that case George L plugs wouldn't open the shunt on an input jack even though Switchcraft plugs would.

    So, what's she like? All of you who told me the 6G2 is the best but least-appreciated little amp out there were right. Not little, either, cuz the sound is hu-u-uge. Tele paradise -- that singing sustain you get in a tweed mixed with the beautiful highs in a blackface and balanced clear mids you don't get anywhere else in Fenderland. Sweet sweet breakup, a little even low on the dial if you dig in, a ton -- but so pretty -- as you go through the middle of the dial.

    Thanks to everyone for their kind remarks, support, and remarkable help and patience in my endless research and planning. You all share in the credit: This is an amazing amp.

    Oh, and did I tell you she's a blonde? A beautiful *rough* blonde? Note the dogbone and corner protectors. I think they lend her a bit of what I'm calling "Showman-ship." And the speaker CJ recommended? Somewhere between a Jensen C10R and a CTS ceramic from a SR. Yeah, she's all that!

    6G2 - 1 (7).jpg

    6G2 - 2 (4).jpg

    The nameplate? Turns out an amazingly generous friend has access to an industrial laser cutter, and went to a *ton* of care and effort to make it. Oh, and Pennington? a great little town not too far from... Princeton.

    6G2 - 3 (4).jpg
     

  2. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Great! My 5f11 ended up getting two 33k resistors paralleled to get a decent bias range, so 16.5k I guess?
     
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  3. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Oh my. Oh my.

    I need some more time to soak this in. -K
     
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  4. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    I'll add to that and say that with my 315-0-315 PT, my vintage bias level was so cold that I thought my meter was broken. The paralleled 33k's got it right. And I'd heard a lot about the 5f11 - 99% the same as your 6g2 - needing a colder bias for the tremolo to work right, but 68% still had mine pumping strong at 368-370v once I got it settled.

    I like the cabinet too. I do the same thing. I've never used a wood screw on any of my cabs. All tnuts and machine screws. The baffles to. Parts Express has some speaker bolts that are black and come with a washer that are great. Congratulations on a real beauty!

    EDIT: I have a 10k bias pot on mine when I settled on the 2 x 33k resistors. Just for clarity.
     
    Last edited: Oct 31, 2017
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  5. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Dang, King Fan! That's AWESOME! I'm really jealous! Can you believe that you BUILT it?! Isn't that so cool? I hope that I'll have built a 5f2a in the next couple or three weeks.

    I love the Pennington thing! I know Pennington, NJ. I've always been fond of the Princeton, not only because of the sound, but also because we lived in Princeton, NJ for four years while I got my Ph.D.

    Congratulations! I WANT TO HEAR IT!!!
     
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  6. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    @King Fan, congrats! That is a really, really great looking amp. The entire build quality is as good as it gets. I think you just up'd the general reputation of all us Shock Brothers builders here!

    Good job on building a unique amp in great attire. A tuxedo Princeton in Blonde Tolex. I can't recall ever seeing one like it anywhere.

    I have a warm spot in my heart for Blonde amps. It is my favourite of all the Fender colours. An interesting tidbit of info: Did you know that all vintage Fender Blonde amps (except 1) are Piggyback head/cab configurations? Only one Fender combo amp was originally sheathed in Blonde. The Twin.

    My Wife and Son smiled as I passed your amp pics around the dinner table tonite. Corneli Elec Instr Co. We know the place!

    I know it sounds great. Are you noticing much difference with or without the NFB connected? I preferred to leave my NFB not connected. I was going to make mine switchable, however opted not too. It sounded better to me with no NFB, ever.
     
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  7. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Dang. I never tried my 5f11 without NFB. Now I'm jonesing...
     
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  8. Nickfl

    Nickfl Tele-Holic

    683
    May 24, 2016
    Florida
    Very nice looking build! Can we look forward to some sound clips?

    How do you feel about that Weber DT speaker? I came real close to ordering one this evening for my upcoming Princeton reverb build, but ended up going with a 10F150T instead. It seems like it is probably a good fit for a brown era amp.
     
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  9. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Having a look at this amp again this morning... this has got to be one of the most beautiful amps I've seen. I've seen the inside and the outside, and I haven't even heard it. I'm sure it sounds as good as it looks. I'm jealous! The blonde tolex is tremendous, and the faceplate is the cherry on top. I really like the look of the brown Tolex era Fender amps, but I don't think I've ever seen a Fender amp--or any amp--that is such a looker as this one!
     
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  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks for your kind remarks, FL. You may be right. That shielded cable -- the stuff Doug sells -- looks beefy, but each of those 6+ inches weighs less than 2g. I hope allowing its natural arc will decrease stress and movement where the weight rests on the tiny center conductor at the ends. Also I try to limit motion by making a support / stiffener of the ground wire at the grounded end.

    IMG_5665.JPG

    Hey, do you think maybe I spent *too much* time thinking about this build? :D

    Thanks again, Keith, for all your help on this amp. Say hi to your family and thank them, too. No NFB? That's an interesting idea -- I've only heard it without NFB for a minute or two during testing. I'll have to try it -- good idea. And if I like it I'll fit a switch. I always like to be able to go back to 'stock' -- and somehow the only lead that ended up too short to hug the chassis was the NFB lead, so a mini-switch would be an elegant splice. ;)

    Interesting you should ask -- although I had Weber do their free factory break-in, I actually stuck it in my PR the last few days to break in a little more. The trick with recommending speakers is that we're all headed for different targets, and somehow that's especially true for PRs.

    In the 6G2, I think you're right that it'll be great. Give me a month to be sure. Designed by Ted Weber with input from Lord Valve for Derek Trucks? Not three people I know a ton about, but pretty good credentials. And I've had really good results on speakers CJ suggests when I email him about my targets. This one? Big, very present and immediate, *big* magnet to generate oomph, but he says a fairly small voice coil to break up nicely and limit efficiency (they were designed to go in a 4-plex SR for DT). Amazing sparkle, but definitely not shrill. Extremely touch sensitive. And break-up? Is there such a thing as melting break-up... like buttah? :)
     

  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Very helpful, Jason, thanks. You just saved me from ordering in, and soldering in, a bunch of smaller resistor sizes!
     

  12. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    I found the tone knob more effective with NFB disconnected. I like some bright sparkle. Turning the amp volume up, yields thicker bottom end from the power tubes. Ajust tone for top end tastes. I found with NFB disconnected, I was more effectively able to dial in the highs I preferred.
     
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  13. r_o_b_s_o_n

    r_o_b_s_o_n TDPRI Member Gold Supporter

    Age:
    35
    44
    Jun 16, 2017
    Victoria BC, Canada
    Your build definitely gives me a level of quality and attention to detail to strive for!!

    Beautiful and inspiring work!!

    Thanks for your help with my 5F1, and sharing your build with us!
     
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  14. kleydejong

    kleydejong Tele-Meister

    459
    Aug 30, 2010
    Orange City, IA
    Wow, stunning build! Nice work.
     
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  15. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks, all, for your kind words. Every one of you has helped me or inspired me or both, from Rob to Robson — who just had the straightest bus bar I’ve ever seen.

    Postscript. I’d be remiss if I didn’t mention the trem. It slays.

    Now we’re off for a few days to visit some remote canyons.
     
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  16. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Where did you end up with your bias resistor & setting?
     

  17. CoyotesGator

    CoyotesGator Tele-Meister

    309
    Jul 12, 2014
    Gulf Coast
    @King Fan, That is a spectacular level of build quality others will strive for.

    Very nicely done
     

  18. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Haven't been back in there yet, so I have the stock bias 'range' resistor but a 24k instead of 30k off the pot to ground. At max, that gives me my 60-70% dispersion. I'll try your suggested value when I go back in there -- I need some range to go higher with other 6V6s. The ones I'm using are old Ken-Rads, are slightly mismatched, but bias up very easily.

    CG, I really value your support and thoughtful comments. Thank you, my friend.
     

  19. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City

  20. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Small updates:

    Thanks to @keithb7 for the great idea about an NFB lift. I did put mine on a switch -- the NFB wire routing goes past acres of empty chassis surfaces. This may be the perfect amp for an on-off NFB approach. (I found simple 'off' to be way too much on my 5f2a and 'almost too much' on my PR). I won't keep it lifted -- my guess is it'll be on : off in maybe 70:30 ratio -- but wow.

    The reason it's great besides *how much* is *what* it provides -- just the right amount of extra OD. I'm finding out why folks go all weak in the knees for 6G2 drive. First, it has a long and gradual increase on the dial. You can get nearer and further from that magic 'edge' over a long span of rotation. But the NFB lift brings it forward -- it's right there, and it's an amazing crossover between tweed and BF OD. Tweed OD (before it goes all Neil)? I say singing cello or oboe. BF (at least on my PR) is like Sam Cooke singing with Billie Holiday -- subtle, melting, bee-stung honey. But 6g2 OD (until it goes all Who in your face) is like those tiny temple bells (silvery jingles? angel chimes?) they play when the young hero goes into a mysterious temple in the Himalayas where he'll meet a wise monk and get his weary soul renewed.

    Whew, did I say that? Gotta get me a wine-tasting show on the local cable channel. :D

    Then, @jsnwhite619, thanks to your advice, I tried a 20k resistor to ground off the bias pot. With my current tubes, it seems to give me the right span above and below my 60-70% dispersion targets.

    Final upgrade (I knew I'd probably do this based on my PR and Vibro Champ) was a .02 cap in the middle of the trem chain instead of a .01. This slowed the slowest trem from about 220 bpm to around 120. Can you say, "throb"? The Mallory I had in the spares drawer is a lot smaller than its Dijon neighbors, but if you're keeping score, they're .02, .02, .01 as you go L-R.

    6G2 - 1 (12).jpg

    6G2 - 2 (6).jpg
     
    Last edited: Nov 10, 2017
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