Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on September 28, 2021, 06:59:11 pm
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I would like to use a brass grounding plate for an AB763 build. Does anyone have a source to buy this or even a source for the materials? All i can find is 12" square pieces of brass sheet metal which isnt long enough
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These guys (http://www.solandfa.com/Products.asp) have brass grounding strips in the chassis kits. You'll have to contact them to see if they sell the strip by itself.
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I would like to use a brass grounding plate for an AB763 build.
Why?
You don't need it. Just use a ground buss wire.
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https://www.amazon.com/uxcell-Brass-Sheet-Metal-1000mm/dp/B08ZJ7WHSJ/ref=pd_di_sccai_1/140-0297308-1570070?pd_rd_w=jd2Ow&pf_rd_p=c9443270-b914-4430-a90b-72e3e7e784e0&pf_rd_r=HDERDTESEQ0KQVJSS1MK&pd_rd_r=d031f749-ae19-4391-bf38-d41e43cec468&pd_rd_wg=xhZaj&pd_rd_i=B08ZJ7WHSJ&psc=1
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https://www.amazon.com/uxcell-Brass-Sheet-Metal-1000mm/dp/B08ZJ7WHSJ/ref=pd_di_sccai_1/140-0297308-1570070?pd_rd_w=jd2Ow&pf_rd_p=c9443270-b914-4430-a90b-72e3e7e784e0&pf_rd_r=HDERDTESEQ0KQVJSS1MK&pd_rd_r=d031f749-ae19-4391-bf38-d41e43cec468&pd_rd_wg=xhZaj&pd_rd_i=B08ZJ7WHSJ&psc=1
I looked at that and it is .1mm. online someone measured the thickness of their plate and they said .4mm
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https://www.amazon.com/ZQQZ-Brass-Sheet-Metal-Plate/dp/B09B5FGTP3/ref=sr_1_3?dchild=1&keywords=.4mm+brass+sheet&qid=1632876280&s=industrial&sr=1-3
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https://www.amazon.com/ZQQZ-Brass-Sheet-Metal-Plate/dp/B09B5FGTP3/ref=sr_1_3?dchild=1&keywords=.4mm+brass+sheet&qid=1632876280&s=industrial&sr=1-3 (https://www.amazon.com/ZQQZ-Brass-Sheet-Metal-Plate/dp/B09B5FGTP3/ref=sr_1_3?dchild=1&keywords=.4mm+brass+sheet&qid=1632876280&s=industrial&sr=1-3)
:l2:
Who's your Huckleberry?
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Why that would be josey. :icon_biggrin:
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Why that would be josey. :icon_biggrin:
Not Doc? :icon_biggrin:
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Doc is a huckle bearer. Big difference. Val just got the line wrong. :l2:
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https://www.amazon.com/ZQQZ-Brass-Sheet-Metal-Plate/dp/B09B5FGTP3/ref=sr_1_3?dchild=1&keywords=.4mm+brass+sheet&qid=1632876280&s=industrial&sr=1-3
my man. :worthy1: thank you!
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Grasshopper, you too can learn to do this in time.
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For future reference: in an Amazon link, everything from "/ref=.." onward is a tracking link, NOT needed to link to the product.
https://www.amazon.com/ZQQZ-Brass-Sheet-Metal-Plate/dp/B09B5FGTP3
That usually makes an Amazon link short enuff to fit on one line.
Though you really should not need brass strip. If a bus-wire isn't good enough, more won't be much better, you should consider what nasty currents you are forcing in "ground".
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For future reference: in an Amazon link, everything from "/ref-.." onward is a tracking link, NOT needed to link to the product.
I never realized that. I'm sure I'll forget it in a few days. :laugh:
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Is there any advantage/disadvantage to brass plate or brass sheet over brass tubing or bar? Most of the old organ amps I have worked on, used brass tubing. I always figured it was used because it was stiffer and roughly 2X cheaper than it's copper equivalent by weight. Pennies counted back then.
Its conductivity is roughly 3.5X less than copper however.
What advantage would brass plate offer?
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What advantage would brass plate offer?
I don't know about brass verses copper, but I'm not sure anybody ever figured out exactly why Fender used the brass grounding plate.
Some say it was easier to solder to than the steel chassis, some say it was used as a better conducting ground plate for the random grounding Fender used. :dontknow:
But we do know that we can use a different grounding scheme, a wired buss, that's better than the plate.
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What advantage would brass plate offer?
I don't know about brass verses copper, but I'm not sure anybody ever figured out exactly why Fender used the brass grounding plate.
Some say it was easier to solder to than the steel chassis, some say it was used as a better conducting ground plate for the random grounding Fender used. :dontknow:
But we do know that we can use a different grounding scheme, a wired buss, that's better than the plate.
Not according to this guy. Is he wrong?
https://youtu.be/kJ3zQUScov4?t=46 (https://youtu.be/kJ3zQUScov4?t=46)
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Not according to this guy. Is he wrong?
Yes and no.
The guy who built the kit used the back of the pots as a ground, probably least preferred way of grounding the pot connections. Your depending on the pots body metal to be low resistance and for the pots connection to the chassis to be good. As time goes by the connection to the chassis from the pots body and star washer will probably loosen and/or get corroded and you loss your ground. Many old amps the fix was to take out the pots and jacks, clean them with deoxit/fine brass wire brush/fine grit sand paper and reinstall them tightly.
So the guy fixing the amp put in the brass plate to use as a ground plain, instead of grounding on the back of the pots. This is better than the way it was, but......
There's a few ways to do grounding for the pots.
1. You can solder a buss wire all the way across the back of all the pots, and run the grounds from the pots to the buss wire. Then ground 1 end of that buss wire to the chassis. But it can be a pain to get the buss wire to stick to the back of the pots. You have to wire brush them or use sand paper to the the solder to stick. And you run the risk of over heating the pot if your soldering skills aren't great or you run into problems with the pots metal used for it's body. No thank you. :laugh:
2. Or you can run the buss wire across the amp without connecting it to the pots bodies. A lot of guys do this with great results.
3. Or you can run your buss wired, from 1 ground star to the next ground star, across the length of the eyelet/turret board. This works great too.
Guys here have built dozens of amps here using the ground buss in 1 form or another and they are all very quite builds.
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Not according to this guy. Is he wrong?
Yes and no.
The guy who built the kit used the back of the pots as a ground, probably least preferred way of grounding the pot connections. Your depending on the pots body metal to be low resistance and for the pots connection to the chassis to be good. As time goes by the connection to the chassis from the pots body and star washer will probably loosen and/or get corroded and you loss your ground. Many old amps the fix was to take out the pots and jacks, clean them with deoxit/fine brass wire brush/fine grit sand paper and reinstall them tightly.
So the guy fixing the amp put in the brass plate to use as a ground plain, instead of grounding on the back of the pots. This is better than the way it was, but......
There's a few ways to do grounding for the pots.
1. You can solder a buss wire all the way across the back of all the pots, and run the grounds from the pots to the buss wire. Then ground 1 end of that buss wire to the chassis. But it can be a pain to get the buss wire to stick to the back of the pots. You have to wire brush them or use sand paper to the the solder to stick. And you run the risk of over heating the pot if your soldering skills aren't great or you run into problems with the pots metal used for it's body. No thank you. :laugh:
2. Or you can run the buss wire across the amp without connecting it to the pots bodies. A lot of guys do this with great results.
3. Or you can run your buss wired, from 1 ground star to the next ground star, across the length of the eyelet/turret board. This works great too.
Guys here have built dozens of amps here using the ground buss in 1 form or another and they are all very quite builds.
Thanks for the explanation. With option 2, how are the pots grounded?
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Read this on grounding, then read it again and again and think about it, then read it again until you fully understand it.
I read it over and over again, before I got it, along with other information on 'wired ground' schemes with ground stars wired together, ie; galactic grounding.
Keep the heavy power amp chassis ground star separate from the low current preamp chassis ground star. Use less random chassis grounds as possible. And keep the ground loops for the +/- of the B+ filter caps and the circuitry they supply as short as possible. Which includes running the PT's B+ CT directly to the 1st B+ filter caps ground lead.
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Thanks for the explanation. With option 2, how are the pots grounded?
You run the pot ground wires to the ground buss wire. They are MANY pictures on this site of guys doing this.
He used a brass ground plate and ran the pot ground wires to the plate. I'm saying to substitute a ground buss wire for the brass grounding plate.
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Thanks for the explanation. With option 2, how are the pots grounded?
You run the pot ground wires to the ground buss wire. They are MANY pictures on this site of guys doing this.
He used a brass ground plate and ran the pot ground wires to the plate. I'm saying to substitute a ground buss wire for the brass grounding plate.
Thanks my friend. One more question. With option 2 on an AB763 for example. The vibrato channel Treble and Bass pots are not grounded via lug. So how do they get their ground?
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This sluckey build document shows a nice ground bus . . .
https://sluckeyamps.com/VAC15/ac15.htm
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The 1st amp I built, back in the mid 90's?, was a Fender tweed Deluxe 5E3. I still have it. :icon_biggrin:
I bought a clone chassis and the brass plate for it and followed the Fender layout and schematic as best I could, it came out alright, fairly quite. But I was lucky. It's not a complicated amp and it's not hi-gain.
I knew very little about tube amps and grounding. From the little bit of house wiring I had done, I thought ground was ground, it's all the same. Right? That was wrong. Ask any good electrician and they will tell you you can't always just grab any ground that's close and tie another ground to it.
If you can get a clear understanding of the current that's flowing through each B+ filter cap and the circuitry it's supplying/feeding, then you'll understand why/how to wire up it's grounding.
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With option 2 on an AB763 for example. The vibrato channel Treble and Bass pots are not grounded via lug. So how do they get their ground?
Yes they are, through the mid pot's ground. They call it a 'tone stack' (TS) because the 3 tone pots are stacked on top of each other. They are all interconnected with each other.
Look at the schematic, not just the layout drawing. Always compare both if available, it will help you. Print them both out to look at side by side.
The TS in an AB763 , if it has a mid pot, 10K, then the TS gets ground from the mid pot. If it doesn't have a mid pot, then it stands on a 6800 (6.8K/6K8) R and that R goes to ground.
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Check my edit in reply #24.
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The vibrato channel Treble and Bass pots are not grounded via lug. So how do they get their ground?
There is no need to ground any part of the bass and treble pots on an AB763 amp. However, the pot body is grounded simply through the nut that fastens the pot to the chassis, but those pots could just as easily have been mounted on a fiberglass board and still operate just fine.
Here's a pic showing my ground buss bar floating behind the pots. The black knobs are an AB763 preamp (R-L, Vol, Tre, Bass). Notice the volume pot is connected to the ground buss but the treble and bass pots are not connected to the buss?
https://sluckeyamps.com/phoenix/p11_big.jpg
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Here's a pic showing my ground buss bar floating behind the pots. The black knobs are an AB763 preamp (R-L, Vol, Tre, Bass). Notice the volume pot is connected to the ground buss but the treble and bass pots are not connected to the buss?
Well, not directly, but the bass/treble pots are connected to the ground buss through the 6K8 R that sets the mids.
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... the bass/treble pots are connected to the ground buss through the 6K8 R that sets the mids.
One end of one pot. Through lots of ohms. That's not "grounding the pot".
Sluckey must play a LOT of mids to need a 2 Watt resistor there!
(Yeah, I see, like much electricals, it is about mechanical robustness not about electron comfort.)
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Sluckey must play a LOT of mids to need a 2 Watt resistor there!
(Yeah, I see, like much electricals, it is about mechanical robustness not about electron comfort.)
egg zackly... You must have looked at the pdf document. :wink: