Finally, at long last, that 5G9 build...

Discussion in 'Shock Brother's DIY Amps' started by King Fan, May 27, 2020.

  1. The Ballzz

    The Ballzz Tele-Afflicted

    Age:
    65
    Posts:
    1,643
    Joined:
    Apr 11, 2016
    Location:
    Las Vegas, NV
    @David Barnett

    I'm not sure that I'm seeing any "lovely cathode follower" that you mentioned in any of the amps being discussed, 5E9-A, 5G9, 6G9 or 6G3.

    Please Enlighten Me?
    Gene
     
  2. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Thanks, @tubeswell , for this and all your good info over the years. Yeah, you shared some PT goals like that -- they became my goals.

    As I said, I stubbornly added one other goal, to get a PT that would fit in my Bandmaster-sized cutout but still come as close as possible to 300-0-300. FWIW I don't think that's the size of the Triad 8160 (see photo above). In fact, Weber sells a W025130 'Tweed Tremolux' PT that fits 2.8 x 2.25" bolt holes -- it just doesn't drop in to their 5e7 chassis. Which makes perfect sense. Behind every great parts problem is a chassis problem..

    After a long search in initial planning several years back, I settled on the ClassicTone 40-18029. If you can cap the extra wires, what's not to like?

    ClassicTone 40-18029.png

    And then, in March, when I was finally ready to order the big stuff, Chicago shut down and ClassicTone stopped winding. One option woulda been Mercury Magnetics, who make not one but two PTs for the 5G9. They were very helpful in my original search, emailed back the same day, but I noted that the lower-voltage of the two still came in at 320 HV, which was too high for me. And then when I got desperate, of course, California had also shut down and MM was not winding either.

    I tried Edcor, too (great iron by all reports) but aside from the fact I never seem to be able to find lay-down formats there, they always build on order, and their standard multi-weeks wait just wasn't gonna work for me.

    One 'new' resource for PT hunters is AmpPartsDirect. They used to handle the CT line, but some kind of small-business breakup happened and they're now apparently working with both Heyboer and MM to build new lines of transformers that will replace their CT listings. They talked about custom winding as a possibility. They were also very helpful -- but in the middle of March, were stuck in covid limbo like the rest of us.

    So I contacted @jsnwhite619 who knows all the paths through the dense Hammond forest, and found something I was sure would work, the imposingly-named Hammond 290D2X.

    Hammond 290D2X copy.png

    This turns out to be a thing of beauty, a punk Medusa with wild Rasta dreads...

    679B7F83-89B6-4888-8680-15D7F0C5D5AA.jpeg

    Dropped into the cutout like it was born there, too. In fact, I can only picture one negative -- with 300mA on tap, my puny little 3-nonal, 2-6V6 amp wasn't gonna load it down much, so I figured my voltages may still come in a bit high. But I also figured it would stay cool -- maybe I could rest my beer on the cab above it and it would act like a drinks cooler. :D
     
    Last edited: May 28, 2020
  3. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    With the PT sorted, time to start prepping the chassis. This is always a thing -- even on my custom kit chassis's, I've had to drill out or move mounting holes, etc. But this Weber stainless steel chassis presented me with three bigger challenges I knew about:

    1. It's a 5e7 chassis, and the existing mounting holes just weren't in the right places.
    2. Stainless steel is really hard. Drilling galvaneal is like butter compared to SS.
    3. The chassis is beautiful, and I didn't want to scratch and dent it.

    Turns out there's a fourth challenge: The inside of these beauties is a true hall of mirrors. We've seen builds in Weber SS where troubleshooting was almost impossible because every wire was perfectly reflected. Questions be like, "Where do those four yellow wires go?" In fact, it turns out to be so perfectly mirrored that I was getting eyestrain just looking in there. Besides troubleshooting photos, I like to detail my build as I go for clarity and later reference. And in photos here, you didn't see one reflection, you saw multiple reflections receding into the distance. Good photo lighting just made it worse.

    559A4E5F-7D09-4D86-9828-5DFCBC49DE39.jpeg

    But being oh so very clever, I dreamed up a perfect fix. Was there such a product? Oh yeah, and it turned out to have great reviews. And yep, really easy to apply:

    C00AA6C2-C132-4C75-AA77-C6ACD606137D.jpeg

    Now that looks pro, I thought, like zinc chromate inside a P-47. Then I went to test fit my board.

    IMG_5081.jpeg

    And you guessed it, on removal, the back of the eyelets had gouged and scratched the coating like it was fog on a window. This stuff may stick to glass, but it doesn't stick (duh, KF) to mirrored stainless.

    The obvious solution was sandpaper. And by the time I'd sanded the entire surface clean (150 grit; good forearm conditioning) I realized maybe I didn't need any spray.

    BB8D375D-6BC5-4F37-9EAF-CF6CE5ED70A2.jpeg
     
    Last edited: May 28, 2020
    theprofessor, Paul-T and D'tar like this.
  4. jsnwhite619

    jsnwhite619 Friend of Leo's

    Age:
    36
    Posts:
    2,990
    Joined:
    Sep 10, 2013
    Location:
    Georgia
    Have you picked your OT yet? Out of my Harvard builds, I've done a couple the exact same except 8k vs 6.6k OT's. The 6.6k was drastically cleaner. Since your PT is obviously not going to break a sweat, if you want much breakup and saturation, I'd definitely go with an 8k output.
     
  5. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Good point. I've always used 8K:8ohms for my '6V6' tweeds anyhow, so I ordered in a CT 40-18022 just like I used in my 5E3:

    40-18022 copy.png

    TubeDepot still had these on the shelf, and they had my choke as well, the CT 40-18040. They were super-helpful too -- in fact, everyone I worked with during the early covid craziness was awesome.
     
  6. David Barnett

    David Barnett Doctor of Teleocity

    Age:
    63
    Posts:
    12,816
    Joined:
    Mar 17, 2003
    Location:
    The Far-Flung Isles of Langerhans
    2nd stage of the trem oscillator
     
    D'tar likes this.
  7. David Barnett

    David Barnett Doctor of Teleocity

    Age:
    63
    Posts:
    12,816
    Joined:
    Mar 17, 2003
    Location:
    The Far-Flung Isles of Langerhans
    Is that a 6G11 on their home page?
     
  8. Intubator

    Intubator Tele-Holic

    Posts:
    555
    Joined:
    Feb 24, 2019
    Location:
    Bawlmer, MD- Home of the "Mayor Shuffle"...
    Looking forward to following your thread here King Fan!
     
    King Fan likes this.
  9. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    As I said, my chassis only had a few mounting holes, and they were in the wrong places. So I found some good info online about drilling stainless. Two big points:

    1. It gets a lot harder as soon as it gets hotter. So don't heat it -- drill as slowly as your drill will work, push down as hard as your drill bit will stand (wear safety glasses), and drill in short pulses (seconds, not minutes) to let the work cool. Cutting oil can help some too.

    2. Clamp it *really well* Much more than regular steel, it wants to seize the bit just as you punch through. Oh baby does it. I'm glad my workbench is anchored to the floor and has a big 2x12 clamp on the side.

    A couple other points. You don't totally need cobalt bits, but get a couple (carbide is apparently too brittle for home use, or at least for a hand drill). Luckily we're usually only drilling two or three sizes, often in small fractions like 9/64, so buying individual bits is an option.

    A *good* center punch is your friend. Can you see where I changed my mind about a hole but left the punch mark? And bigger holes are actually easier, within reason, partly because you can really push down on a big bit. My best hole is probably the left bottom grommet hole -- the other two are factory. You can obviously tell my holes from factory, and you can see the one that 'walked' -- my first bottom OT mounting hole was drilled in the wrong place.

    CCAA2ED8-87CC-408E-8257-579E56061F21.jpeg

    Finally, a wonderful feature of the Weber chassis is the copper threaded ground stud welded to the chassis. Now that's a solid ground anchor.

    Before we leave the wonders of the Weber chassis, note they provided a nice tech drawing that really really helps in planning. Here it is with some of my annotations:

    Weber tech drawing detail.png

    For example, you'll note the 1.125" octal socket holes. Will they fit my Belton sockets? Here Doug Hoffman had me covered. He says, "Mounts in a 1.18 inch chassis hole for top or bottom mounting. Can also be mounted in a .99 inch hole for bottom mounting using the small diameter section of the socket."

    So once I reminded my brain that 125 is not larger than 18 when preceded by a decimal, I also realized 1.125 *is* larger than 0.99. So bottom mounting it would be. Which worked perfectly.


    405B30F3-C06E-4C6D-BEE0-4F4112FDC011.jpeg


    0CAFFDE9-8860-4581-A2A7-BDEF73E070FA.jpeg
     
    Paul-T likes this.
  10. Paul-T

    Paul-T Tele-Meister

    Posts:
    417
    Joined:
    Nov 23, 2018
    Location:
    London
    Looking good!

    And that's excellent hole-nerd detail. If I'd realised you could mount with the lugs like that, I could've save myself a day cleaning up alternative sockets to my Beltons. A good reminder to keep Doug Hoffman's as a daily reference.
     
    King Fan likes this.
  11. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Yes, and opening up the holes in stainless did not appeal!

    So, with 14 or 15 new holes drilled, time for some pre-building. The weight of that PT (something over 8 lbs. I think) made me realize I'd want a hanging bracket like the big boys used -- Bassman etc. A query to the smart folks here gave me several great ideas, including this sturdy L-bracket suggested by @dunehunter , who builds entire fleets of cabs.

    3D89661D-C93D-44CD-89F4-EF5D3449D2A0.jpeg

    Then build some stuff that's easier to assemble on the outside of the cab than inside.

    818B9F23-D7AA-4249-B1F5-9769D3523996.jpeg

    4993F229-1C8F-4C59-87E4-3C41A1ADA2B4.jpeg

    093001D6-F122-4305-8EDB-49A7B8871770.jpeg

    FDA75B6E-75EC-423E-B2F8-8BB8D8F3352F.jpeg

    Note to self: Even doing outside mounting (I usually do inside) the bits hanging so far off the octals weren't a problem, since you could tilt the assembly to slide into its hole. But if you added more bits, like 100Rs to elevate the heaters, it might get ugly. And the simple jumpers and the resistor across the nonals? Turns out they need to be done with the lugs vertical -- if they splay out at all, they won't fit up through the holes. And nonals with shields don't allow for inside fitting.
     
    Last edited: May 29, 2020
    monkeybanana and dunehunter like this.
  12. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Next, power wiring. Some folks do this last, but it's kinda the most important thing in the amp, and even with a smaller PT, safety needs suggest building this in a wide-open space. Electrically and mechanically separate anchor bolt (it's UL, dude) sorta where Fender used to solder ground to the chassis? Layer star washer, crimped-and-soldered ring terminal, then a keps nut with loctite? Green longer than black or white? Black to fuse tip and then on to switch? And for a nod to the 21st century (actually the EU has required this for a long time) let's switch both hot and neutral.

    B15F83E2-0B40-4CBD-A473-FA93F708BC0B.jpeg

    Side note to new builders; get some cheap imitation-Heyco 'strain relief pliers' to mount your power cord. Though your children will be deprived of learning a dozen new curse words, your own life will be forever improved (different amp, same sigh of relief).

    A82EE1A2-122B-4209-AD94-C89C2F47E87D.jpeg

    Now to wire up the heater string. Usually I mount the PT very early in the process, following the brilliant test-as-you-build strategy of Steve Luckey (see reply #3 here). But with the weight of this PT, I was worried the whole thing might plunge to the center of the earth through my workbench, so I decided to test the PT secondaries in place after the amp was mostly wired up. So sockets in place as seen above. I decided to get real Belton bearclaws, because... shiny.

    42FC60C8-B5AB-4875-A32A-5FC4A73A27E2.jpeg

    I still like 18ga between the output sockets -- why not, they have (um, fairly) sturdy lugs with big holes in them. But I've gone to using 22ga to the preamp -- Marshall used it for the whole heater string, I'm told, and it is so much easier to train across the small sockets and shape into those gracile preamp lugs.

    21ABB159-8A52-42DD-A13F-EBECB4EAF40F.jpeg

    74C84DC8-1F53-40DD-8E4A-94C2A7C8F142.jpeg

    One green strand gets marked with a Sharpie so I can swap phase in the push-pull pair, and though phase doesn't matter much on dual triodes, using two different colors makes it easy to see what goes where if you care. Even with 22ga, diving it through the socket and keeping it twisted until it gets there (a la Merlin Blencowe) is hard enough.

    FWIW, I built my first tweed with flying overhead heaters (I still do in a tray-style BF chassis), but I've since listened to the wise ones here who point out that in tweeds they totally block later access to the board, and I've taken up the 'under-the-rim' style instead.
     
    Last edited: May 29, 2020
  13. chas.wahl

    chas.wahl Tele-Meister

    Posts:
    133
    Joined:
    Dec 8, 2012
    Location:
    NYC
    Reading with interest!

    A few facts about stainless steel that some people may find surprising (for consideration when choosing material for a chassis):

    a) The thermo-electrical conductivity of stainless is about 1/5th that of carbon steel. Apparently, grain-oriented steel is more like stainless in that regard.

    b) I guess that most people who would read this forum are already aware that some alloys of stainless steel are non-magnetic (austenitic) and some are magnetic.

    c) As the above conversation makes clear, stainless is noticeably harder than cold-rolled steel due to the additional nickel and chromium, even though its tensile strength and modulus of elasticity (not really big concerns for amp building) is only about 2/3 that of CRS. It is very hard on tools, and difficult for a home-builder to work.

    d) Stainless is not really "stain-less" as a guaranteed permanent property through and through. The "stainless" property is a surface-only thing, the result of (reactive) chromium forming a very thin, invisible and reasonably hard oxide, passively (on exposure to uncontaminated air). That oxide layer can be damaged, though, by abrasion; and the "re-passivation" process can be subverted by contaminants thus introduced. Stainless that's routinely exposed to harsh environments, and has its oxide layer disrupted, can proceed to alarming corrosion just as fast as non-stainless steels. Repeated exposure to salts is a common initiator. Moreover, unqualified fabricators (like XYZ Welding company who thinks they can do a stainless job) will often use the same tools to fabricate stainless as they use for carbon steel -- with the result that they embed carbon steel particles into the stainless surfaces, and more or less permanently prevent them from passivating effectively. The "fix" for this is generally not to resurface the stainless, which will mainly just spread the contaminants around, but to submerge it in nitric acid (which nobody should attempt at home). The 316 alloy of stainless is "more stainless" than the more common 304 alloy, but still not entirely immune to this.
     
    monkeybanana, King Fan and tubegeek like this.
  14. tubegeek

    tubegeek Tele-Afflicted

    Age:
    59
    Posts:
    1,769
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    That was definitely a lot of info I've never seen before, thank you for adding this to the discussion. Reading with interest, indeed.

    I've gotten about as far as "It is very hard on tools, and difficult for a home-builder to work" before giving up. I don't have the proper gear to do anything with stainless, I've tried. Too bad - it looks so nice.
     
    King Fan likes this.
  15. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Excellent info indeed, and some awesome new words. Autenistic! Passivating! Thank you.

    I'm thinking from what you say that my sanding will render the inside prone to corrosion. Living on a hill in Utah, this won't be an issue. If you lived on the beach in CA or FL, it might though.

    I won't choose stainless much, but Weber's shop did a great job with this one, and the outside's shiny beauty has some real advantages for tweed. No chrome peeling here.

    And although it's hard, it's not impossible to drill. Some guy who builds bluewater sailboats said with slow high-pressure lubricated intermittent drilling he actually drilled twenty 3/8th inch holes in stainless deck fittings -- with an HSS bit. I suspect YMMdefinitelyV.
     
    Last edited: May 29, 2020
    tubegeek likes this.
  16. CapnCrunch

    CapnCrunch Friend of Leo's

    Posts:
    2,960
    Joined:
    Jan 7, 2011
    Location:
    Washington, USA
    The metallurgy of various forms of mild steel, simple 10 series high carbon steel, hybrid tool steel, and complex hybrid stainless steels, is really fascinating. For amp builders though, I suspect one of the most important considerations is in paragraph a) above. I've always been sort of mystified by how eddy currents work in a chassis and what type of grounding scheme is most effective in a case like this where the chassis has 1/5th the conductivity of a cold rolled steel chassis. Compared to an aluminum chassis, the difference must be in 1/10th range I would think. It will be interesting to see how effective stainless is for shielding purposes and how vulnerable the build will be to things like ground loops. I've found aluminum to be really forgiving because of its high conductivity, but maybe I've just been lucky.

    Just a thought. I would be giving a lot of thought to my grounding scheme in a stainless chassis though.
     
    King Fan and tubegeek like this.
  17. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,122
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    Is it too silly to say that I really love your build threads, @King Fan? Seriously, they're great. Lots of narration and lots of close-up pics. And when I've watched your builds in the last few years -- but especially now -- I've gotten a little jealous. So neat and tidy, and with so much forethought! Watching you build amps makes me want to build more and to take on board all the new little perfections you've added into your process. (OK, I'm not jealous of chassis work -- especially stainless chassis work; but the rest...)

    As for the PT: if you ever get bored during your build, why don't you lean down and count the laminations on that power transformer? Holy cow, that thing's a monster! Some questions, if I may, despite my amateurism:

    (1) Since the PT is capable of providing about three times the necessary current, and since, as you mention, that will mean that the PT is basically providing current in its sleep, does that mean that the sound offered by such a PT may be perceived as more "modern"? I know that some folks describe David Allen's overbuilt transformers (http://www.allenamps.com/trans.html) that way. But it's quite possible that it has a lot more to do with factors other than being over-spec'd for amperage. Or perhaps that's really more about his output transformers than his power transformers.

    (2) You mentioned that since the PT won't be loaded by providing current, the voltages might be higher than would otherwise be. If that is the case (and that remains to be seen, I suppose), I wonder about the differences between, say, a PT with 305V secondaries but with 300mA capability (as your Hammond has), as opposed to a PT that may work harder to provide the current the amp needs (say, 100 mA; if one can really define that as "working hard," I don't know) and a secondary winding of around 315-0-315V. That is to say, is the PT's current capabilities, together with its lower secondary winding (305V) going to behave similarly to a PT with lower current capabilities and slightly higher secondary winding (e.g., 315V), since the current-loading may push the overall voltages down a bit? I have no idea of that's how all this really works; I'm simply following what I took to be the thought-process above and extrapolating from it.
     
    muscmp likes this.
  18. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
     
  19. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,191
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Hey, Professor, thanks for your kind words. Coming from someone with your research skills, that means a lot. I guess I'm only able to certify your amp / tube / guitar research skills, but I bet you're a wizard in the college library too. And as for neat and tidy? I seem to recall your recent PR build had some of the tidiest cloth-covered wiring I've ever seen anywhere.

    I'm guessing the 5G9 will sound more 'modern' than some smaller tweeds partly because of the choke, and the big reservoir, and the LTP, and the big cabinet... But if I'm right, a really 'big' PT should certainly get rid of PT sag if that contributes to 'old-fashioned' sound.

    As for your questions about a 'bigger' PT with lower HV v. a smaller PT with higher HV, that is all w-a-a-a-y beyond my pay grade. I have wondered. My idea that PTs on the verge of a nervous breakdown (sorry, film buffs) *may* have less capacity for housework is based on reading the real pros here talk about things like the 75mA Champ PT, say in a PR, when you load it up.

    I'm gonna take a WAG that you have to load up the stressed-out little PT pretty hard before you start to see its voltage drop much. I was trying to watch my 75mA PR PT sag in B+ (on my meter) under load, and I only saw it happen when you played a biggish chord above 7 or 8 on the volume -- an area I don't go a lot on a PR. I'm no EE, and may have done the test wrong, etc. but let me just guess that your higher-HV amp would still put out its rated voltage much of the time. Besides, if this 5G9 is as loud as I expect, I'm not likely to be diming it much. Wiser minds will have to step in here -- for all I know I'm spreading high-nitrogen bovine waste all over the alfalfa.

    But there's a question I've also wondered about a *lot.* The 5G9 has basically the same 3-pot interactive VVT as a 5e3. Will I get all my volume slope in the range of 2 – 4 (OK that's harsh, let's say 2.5 – 4.5 :)) on the volume dial? The 6G3, a sorta successor to this amp as noted above, certainly had a more modern volume circuit. I'd considered fitting something like that here. But no, one of my amp-building goals is to try to hear what Leo and Freddy Tavares intended, at least within reason. So I'm setting the wayback machine for 1960, not 1961...
     
    Last edited: May 29, 2020
  20. theprofessor

    theprofessor Poster Extraordinaire

    Posts:
    5,122
    Joined:
    Aug 8, 2016
    Location:
    Chattanooga, TN
    I think you're probably correct that it would take a LOT more current load to affect the voltages in that way. Maybe some of the pros will step and an explain here. I'd cherish a bit of sidebar-narration on what features of David Allen's PT's tend to make them sound more "modern," if folks are agreed on that description. All that said, I really do like the idea of a 305V secondary.

    I was also thinking -- and I didn't mention this in the previous post -- about the advantages of trying to "correct" the voltages at the power transformer on our builds (as we are often wondering about) versus "correcting" the voltage at the wall with a voltage attenuator like an AmpRx BrownBox or the like. It seems to me that, despite the fact that some companies seem at least to be trying to build "voltage-corrected" transformers, none has quite cornered the market on it yet. Your narration of the Mercury Magnetics options for the 5G9 is a perfect case-in-point, despite their great customer service. So then it leaves me to think: rather than us always having to haggle over the PT, what if we just used power-scaling at the wall? Problem solved. For all amps. Right? (BTW, I don't have one of these, and the very fact that I've "corrected" these things at the amp makes me less likely to go back and use the other model of "correcting" at the wall, since I might have to re-jig everything to make it work properly.)
     
    muscmp likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.