Brass Plate Questions and Grounds

Discussion in 'Shock Brother's DIY Amps' started by keithb7, Jan 9, 2016.

  1. keithb7

    keithb7 Friend of Leo's

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    I am currently assembling a Weber 5F2A kit for a friend. I have not built an amp with the brass plate used behind the pots and input jacks before. What is it's purpose?

    Please correct me if I am wrong, but the pots are grounded to the chassis correct? The lugs on the volume and tone pots that need to be grounded can just be grounded to the rear of the pot. Correct?

    The V1 cathode cap at the far end of the preamp side of the board, where should it be grounded? The sleeves of both input jacks also need a ground. Can I solder these 3 points to the brass plate? I do have a large 100W soldering iron if required.

    I have seen on older vintage Fender SF amps that I own, where it appears that grounds are directly soldered to a brass plate under the pots. As seen here in my 71 Super Reverb.

    [​IMG]

    I would like to separate the preamp side grounds, from the power supply cap grounds. Weber has a lug Welded to the chassis near the PT. I was thinking I'll put the PT center tap and the grounds from the B+ caps together at that lug.

    Here is my current 5F2A project showing area of discussion. You can see I have not yet grounded the jack sleeves, of the cathode cap. Your help is appreciated. Thx. Keith

    [​IMG]
     
  2. clintj

    clintj Friend of Leo's

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    Check out Robrob's site for a good ground scheme for the Champ/Princeton type amps. A two point star works very well in these - preamp bussed and connected to the input jack, power section bussed and grounded near the PT.

    The brass plate method and grounding by soldering the pot lugs to the casing does work. However, if the pot comes loose over time or corrosion builds where it meets the chassis, you get random noise that's not fun to chase down.
     
  3. keithb7

    keithb7 Friend of Leo's

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    Thanks Clint. I checked out the info suggested here:

    http://el34world.com/charts/grounds.htm

    I must say I am not very impressed with the quality of parts in the Weber kit. Certain parts are quite poor. The small power cord they supply is too small for the strain relief, so it just slides around with the strain relief locked in place. Effectively useless. I think if you sneeze while installing the lamp assembly it'll break. So much for tightening down the pots real good to make sure they are well grounded. The cheap mounting nuts strip out with very little torque. Very high chance this amp will need replacement parts sooner than later. I will not recommend. If you want to build a 5F2A or a 5F1 see contact Dave at Boothill amps. "hackworth1" on this forum. He's got a ground scheme that works very well with his turret circuit board. Quality parts throughout.
     
  4. andyfromdenver

    andyfromdenver Friend of Leo's

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    you could solder to the plate just for looks. just make sure the joint is shiny and solid. i'll bet it will sound the same or great however you slice it.

    if you are trying to do a straight up clone, just clone the lead dress really well.

    sorry about the cheap parts.
     
    Last edited: Jan 9, 2016
  5. Ricky D.

    Ricky D. Doctor of Teleocity

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    I got stuck for a while trying to solder to the brass plate in my Mission 5E3 kit. I needed three hands: one to hold the wire in place, one for the iron, and one for the solder. :) I finally drilled a small hole at each solder point on the plate to make a mechanical connection.

    On mine, the V1 cathode cap is grounded to the nearest corner of the plate.

    The jacks I have are all metal, so they ground to the plate and chassis just by being mounted. The pots ground the same way.

    The power supply caps are grounded at the corner of the plate closest to the PT.

    The amp is very quiet, FWIW.

    Hope you find this helpful.
     
  6. moosie

    moosie Doctor of Teleocity Ad Free Member

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    Keith, in addition to robrob's site, check out the Blencowe book. Here's the appropriate chapter as a PDF: http://www.valvewizard.co.uk/Grounding.pdf

    Basically "yes" to clintj's two-point star idea. At least this is becoming my understanding. I'm just learning...

    I found this much more informative that the Hoffman site you referenced. I was specifically looking for advice on grounding schemes for a Weber ReVibe, which is arguably potentially the noisiest circuit imaginable if not done right. And because it's not the amp, and plugs into the amp, ground loops are an issue.

    Hoffman's answer was to lift the ground. Blencowe enabled me to understand how I could elevate ground, to separate chassis and preamp grounds. You don't need to go so far with an amp (Leo never did), but too much knowledge never hurt.
     
  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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    There is a very common mod for the Weber ReVibe that eliminates its hum. Google should turn it up.
     
  8. moosie

    moosie Doctor of Teleocity Ad Free Member

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    The Tore T mod, which raises the signal level...

    Lots of dead links floating around. Forum messages to things that no longer exist. Some stuff still on the Hoffman site.

    I looked into this in detail a while back, then got sidetracked by my health (again). I seem to recall the grounding was still an issue, but I'm not sure now. There are so many variations, partial info, some of which I don't understand, etc.
     
  9. keithb7

    keithb7 Friend of Leo's

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    Thanks folks. Some real good reading there. Who knew there was so much to learn about grounding?

    I carried on assembling the 5F2A after reading some of your posts. The pots are grounded as normal through the chassis. I put the main ground wire on the nearest PT mounting lug. The B+ caps are grounded to the back of the tone pot. The PT center taps I grounded together on the lug Weber welded in near the PT.

    Fired it up and played it. The amp is dead quiet. Thanks for your input folks.

    [​IMG]

    [​IMG]
     
    Last edited: Jan 10, 2016
  10. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Re: Weber kits. I would say that you get what you pay for. They're delivering one of the cheapest kits available while still being fairly true to the original circuits/layouts, and to do that, you need to use cheap parts. If a person wants it to look, sound, and feel more like an original Fender, they'll have to pony up a little more. Not a dig at you, Keith -- I just want to slap people who expect the world, without paying for it. ;)

    That said, I've built a couple amps from Weber kits, and I am nothing less than satisfied. :)

    One thing I'd recommend is to add some insulation on the legs of that 500pF tone cap -- if it flexes due to handling, it could short out against the grounded leg of the volume pot.
     
  11. keithb7

    keithb7 Friend of Leo's

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    Good tip thermionicScott, I will put some heat shrink tube on that tone bleed cap.

    I get what you are saying about the Weber parts quality. I hyad not really thought of lower quality parts to keep the kit prices down. Previous parts kits I bought were from Trinity and Boothill. When I did those I was happy what I got, not really having anything to compare them to. Now I have added the Weber kit to my list, I now have more experience.
     
  12. keithb7

    keithb7 Friend of Leo's

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    This one is a wrap. Another member of the 5F2A army. Sending it off now with the new owner for a lifetime of enjoyment. Switchable NFB and switchable multi-tap output transformer.

    [​IMG]
     
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  13. alathIN

    alathIN Tele-Holic

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    Thread resurrection - I'm building a Weber Revibe now.

    I too built a Trinity kit and totally agree - the components are very nice and the documentation / builders guide / support are fantastic. I would not have made it through my first kit without Stephen's help.
    In fact to my relative beginner eye Trinity hits the sweet spot for quality - the stuff that matters most and most failure prone - jacks, transformers, etc - is very good quality. At the same time, they don't blow up their price point by using New Old Stock platinum-in-dinosaur-oil capacitors.
    They also have a bunch of stuff that's different - a HiWatt type, a Dumble type, a Vox/Matchless hybrid. Nothing wrong with Princeton Reverbs and JCM 45s, but it's cool to have some variety available.

    Weber is right up the road from me. I've visited there and met those guys and really like them. They are definitely trying to put out the lowest cost kit to the builder and they are definitely geared to folks with more experience, not raw newbies.
    I like how when you order you can check boxes and get your kit without transformers, without tubes, without jacks, without pots - whatever you want to upgrade, leave it out of your kit and buy your own upgraded stuff.
    And I did get a bad pot with my ReVibe kit - the not-easy-to-find 10meg reverse audio taper one that goes with harmonic trem and, it seems, nothing else. I emailed them and had a replacement in my mailbox literally the next day (might be a little longer if you don't live in Central Indiana).
    A lot of that stuff probably has a U-shaped reliability curve, and as long as you're doing your own QC and weeding out the bad part or two, you'll probably get good use out of what passes your checks. Just my guess, we'll see.

    But I do think Weber kits have their place, if you know what you're doing and know what you want. They definitely have great customer service.
     
  14. moosie

    moosie Doctor of Teleocity Ad Free Member

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    Building a Revibe, eh? Hang on, enjoy the ride. :lol:

    Here's my build thread from a couple years ago. Might help with the grounding. Mine came out dead silent...
     
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  15. alathIN

    alathIN Tele-Holic

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    We've been in touch. Im not just using your ground scheme, I'm using your layout too!
     
  16. moosie

    moosie Doctor of Teleocity Ad Free Member

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    Oh, gotcha ;):)
     
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