Help a newb with a 5f2a journey? King layout

[prsman1981]

So I bought a 5f2a kit from tubeaudiosupply.com and the transformer set from him.

Been pouring over the schematic and Rob Robinette's site along with some Uncle Doug on YouTube etc.

Decided I'd like to try King Fan's layout over mojotone or Weber's.

I'd like to understand the ground bus a little more. Specifically where on an unmodified eyelet board to place it.

Also have questions about grounding the chassis (physically where should I do it? Do I need to drill an additional hole? (I'll post a pic of the chassis.

Also I don't quite understand the splice in his layout. What is its purpose and what exactly am I splicing from/ to.

Hopefully I'll be able to use this to show my progress and ask for advice before I do anything, as I don't know anyone in the St. Louis area who could help in person.

I'll post pics of my chassis later in hopes someone could suggest a place (if needed) to drill for grounding.

 

[mountainhick]

I float my ground bus. Ground buss wire soldered to a ground lug, bolted to the chassis near the input jack(s).

Otherwise it is essentially secured in physical space by all the wires connecting to it, both from the board eyelets and the pots. Once they all are soldered to it, there is plenty of support and it does not move around.

It otherwise can be held in place any way you want. Turrets, raised lugs, stand offs, whatever can be used at a couple strategic points on the board. Don't let it be grounded to the chassis in multiple places though. Only one connection near the input jacks.

There are two quite good common strategies for ground buss,

1: connect all grounds to the buss, all the way from the power transformer center tap to the input jacks

2: Split grounding scheme, PT center tap and plate and screen B+ (es) ground to chassis, and everything else to the ground buss connected to chassis at input jacks.

I prefer #1.

Of course there are other schemes if adhering to vintage layouts, but you're not.

 

[Lowerleftcoast]

questions about grounding the chassis (physically where should I do it?

Welcome to TDPRI

If the chassis does not have a hole for the power cord ground, one should drill somewhat near the power cord grommet area.
I drill the side of the chassis and place the hole so it is easy to access with tools. The ground wire is *long* inside the chassis so if/when the power cord is yanked out the ground stays attached while the hot and neutral wires exit the chassis.

I don't quite understand the splice in his layout.

I think @King Fan is talking about splicing the neutral power cord wire to a power transformer primary wire. If your power switch is capable of switching both the hot and neutral, you may want to do that instead.

I'd like to understand the ground bus a little more. Specifically where on an unmodified eyelet board to place it.

Some like the look of a ground bus wire. The 5F2A does not *need* a ground bus. A simple wire is adequate. Fender routed it under the chassis but you can route it on top. It only connects three eyelets, so some of us just use wire. KISS.

If you choose the ground bus, place it so it has clearance for the input jacks.

 

[chas.wahl]

In case it's not obvious, the point of a ground bus is to provide a unified ground reference for all the various components that need a ground, hopefully in a rationalized order/sequence from power transformer to input jack(s), and involving as few ground loops as possible, or none. That means that it should be connected to the chassis (which gets its ground reference from the incoming mains ground wire, terminated near that point of entry) in one location only, and not touching any other conductive items that are grounded, such as pot bodies, jacks, etc.

These are the basic rules for a "unified bus" -- and DIY builders break them all the time, and get away with very little noise penalty; but sometimes they don't get away with it. The unified bus is intended to avoid such noisy circuitry.

Physically, as pointed out above, it can be as simple as a continuous wire, and supported on eyelets (so long as they are isolated from everything except intentional connections to circuit elements) or otherwise mechanically. For instance, the bus that @King Fan has drawn on outriggers could have outrigger wires from the eyelets as shown, or simply be a wire that's soldered to each of those eyelets. The connection to chassis should be at or right next to one of the input jacks.

 

[King Fan]

I hope our smart friends have helped with your questions. You have a great idea -- post pics and ask more questions about anything you don't fully understand. As they note, there are a bunch of ways to do a circuit ground bus / wire. In fact, I drew about a dozen each for the 5F2a and the related 5F1, exploring options. This is just one of them...

Note the household safety ground/earth near the PT, and the circuit ground (from the bus) on an input jack. As noted, the bus can be a bare wire -- heavy is nice for rigidity -- or several lengths of standard wire. As the guys note, all you have to do is make sure it doesn't contact any other connections on the board and doesn't run into anything (like the input jacks) in front of the board.

There are several topics that actually need more attention than circuit grounding, even in this simple build. As noted, do you have a single-pole or double-pole switch? Does your PT have a heater center tap? What colors are your PT and OT wires? (Wiring diagrams / schematics can help here.) Then we can think about heater CT elevation, the PT's high-voltage center tap, and several other things.

Let us know what is and isn't clear. And enjoy this part. The research and planning phase is the safest, cheapest, funnest, and most important part of amp building.

 

[YellowBoots]

funnest

First time I’ve ever disagreed with you @King Fan

 

[King Fan]

Your questions about fitting the bus on the board are really logical -- though there are many ways to draw it, the trick is making it fit in the narrow chassis with bits sticking in. I like to look at pics of other builds; let's focus on some in a really narrow tweed chassis.

FWIW, here's a wire bus with insulation on a 5F2a (source:TGP) -- you'd just have to find a bare spot to solder the ground from the volume pot, and run a wire from the right end to an input ground lug. (Is it clear that input jacks are grounded through their case contacting the chassis? Smart builders put a star washer under there to assure the connection is solid.)

Here's a nice 5F1 build with a simple Romex core suspended a short distance above the board (source: user @r-o-b-s-o-n on this forum). Note the clearance to the jacks -- this is key.

Here's another very tidy bus on a 5F1 from the forums. Note the builder, who'll be anonymous, was posting cuz the amp wasn't working -- but it can't have been due to poor workmanship.

And here's another tidy 5F1 showing a similar bus on an eyelet board (source: our wise friend @theprofessor ).

We also see lots with a plain bare wire bent to run just north of the eyelets / turrets along the edge of the board. Or lengths of insulation never hurt anyone. Under the board is neat-looking, but not something I suggest to early builders: Out of sight (can drive you) out of (your) mind.

 

[King Fan]

First time I’ve ever disagreed with you @King Fan

So Andy, you're a grammarian in addition to being an amp guru? OK, "most fun"...

 

[YellowBoots]

So Andy, you're a grammarian in addition to being an amp guru? OK, "most fun"...

Still disagree. It’s unpossible for planning to be more funner than building.

 

[2L man]

Also have questions about grounding the chassis (physically where should I do it? Do I need to drill an additional hole? (I'll post a pic of the chassis.

Perhaps you could change the way to think circuits? "Ground" is secondary 0V reference where return current flow back to power supply. Tube amps use DC so it is 0VDC.

A solid bus or few (Star) wires are used for return currents. So always when you see upright T-symbol think 0VDC and return current. Actually return current circuit is simpler than positive feed circuit which has voltage dropper resistors.

Chassis is a Mains Safety Earth which "burn" Mains Fuse if so severe current leak happen that amp own fuse fails to protect. SE wire is mounted to Chassis and a crimped lug which is screw/bolt mounted is preferred.

Chassis is also used as a Shield preventing electromegnetic noise entering to amp and also exit out of amp and SE is used to "ground" this noise. Thats why it is bad idea to use chassis for operative current!!! It has been forbid in many European countrys more than 50 years when appliance is Mains powered.

OVDC is connect to chassis at input jack because it is most sensitive to EMF when amplifying comes highest beginning there. This also lessen noise getting to guitar thru instrument cable.

 

[prsman1981]

Alright. I have some info to pour over and think about now. Appreciate the feedback so far. I do have a picture of my chassis ony phone I'll try to upload now. I marked up a spot on the side close to the power cord hole in yellow. Would this be an ok spot to drill for ground?

 

[King Fan]

Alright. I have some info to pour over and think about now. Appreciate the feedback so far. I do have a picture of my chassis ony phone I'll try to upload now. I marked up a spot on the side close to the power cord hole in yellow. Would this be an ok spot to drill for ground?

Yeah, that side wall is a great place. Many folks drill an 11/64 hole for a #8 machine screw (bolt). I use a 5/8" 8-32 screw. Then best practice is to crimp and solder a #8 ring terminal on the (loop of) household ground wire, fasten that over the bolt with a star washer underneath and a Keps nut on top. A drop of thread locker is the cherry on top. Don't freak out. Much of that stuff won't be in your kit, but a trip to my local Ace hardware usually gets me all of it for a few bucks; add a few more if you don't own a big-but-cheap crimper.

 

[theprofessor]

Hey @prsman1981 . Firstly, welcome to the forum! Secondly, you're in good hands with all the folks who have pitched in here. They all know more than me, though I have built a few good amps. I'll offer a 5f2a build thread of mine as a possible help, but also with an apology. I'm sorry it's so darn long! But I think the advantage of my 5f2a build thread is that I tried to ask all the newbie questions on it to help other people later. I tried not to be embarrassed about such "basic" questions, and my asking them (and generous folks answering them) means that the answers are there for all to see (who have the patience to read through the whole thing). Don't feel like you need to look at it, if you don't want to, though!

A well built 5f2a, paired with a great speaker and cabinet, is darn hard to beat. I hope you enjoy the whole process, from planning to playing. As much as I love the sonic result of a build, I miss the build when it's over. So try to enjoy it! A lot of us will be contributing with information and opinions. You won't always know what to do with all that. But if you can just focus on laying components and wire out very carefully and making beautiful solder joints, that's the biggest portion of what will make your amp successful.

 

[pinchegil]

Enjoy the plan and build process but don't forget to get some guitar playing time as well. I can honestly say since I have been building amps, my playing has suffered.

 

[prsman1981]

I mocked everything in the chassis up last night and got all the chassis components in. I do have a question about the eyelet board and where to mount it. Also, I assume the holes in the board are for all the wires that run under the board and not for mounting. Do I make my own when I find a suitable place to mount it?

 

[theprofessor]

I mocked everything in the chassis up last night and got all the chassis components in. I do have a question about the eyelet board and where to mount it. Also, I assume the holes in the board are for all the wires that run under the board and not for mounting. Do I make my own when I find a suitable place to mount it?

As for where to put the board: look at the layout of the components and superimpose that mentally onto your board. Then you want to put the components at a proper distance to their connections. Once you’ve done that, you also want to mark where to drill holes through your eyelet board to mount it to the chassis itself. When you are marking those holes, make sure there is no interference on the underside of the chassis, like an output transformer in the way or something. Once you drill the hole through the board where you want to go, mark those spots onto the chassis itself. And then drill out the mounting holes through the metal chassis. And as for running connections on the underside of your eyelet board: I would highly recommend running all those connections on the top side of the board. It doesn’t look as neat, perhaps, but if there is an issue with those connections, it is much, much easier to trace and to fix. But yes: the holes that come pre-drilled in the board or for running wires out from under the board to their connections. If you look at the fender layout, you will see that these holes are simply repetition of the way Fender did it. Whether you use them that way or not is totally up to you.

 

[chas.wahl]

Aren"t those 3 holes in the back wall of the chassis for fastening the board? Same "drill" as what @theprofessor says above, but in reverse: make sure the board is positioned so those locations will miss everything topside of the board, and then mark those hole locations on backside of the two boards, then drill them.

It might be easier (though it doesn't look like it, still, safer?) to:
• put a couple pieces of cardboard into the chassis, one going into the lower left corner, one into the upper right
• glue them together (or tape them securely), mark where the PT end is, so you don't get confused
• situate the board where you'd like it, and mark where the corners are on the cardboard
• drill hole locations through of the cardboard pieces, and remove cardboard from chassis
• drill some holes in cardboard where the corners of the board were marked
• put the circuit board(s) on the underside of cardboard template (with both eyelet flange side of board(s) and top side of cardboard facing up), and test-mark where the chassis holes would be
• check and double check that these holes present no problem, including washers/nuts, at those locations

That's how I'd do it, but I'm a long way 'round sort of person. The short method is to forget about those holes in the chassis, and drill new ones through the board and chassis where you know they won't cause any interference. Those fastening points go to ground! The reason I suggest the above is that drilling through those steel chassis is harder than I thought it would be!

 

[King Fan]

Exactly what they said, more or less.

Me? I put the board as far right as I can, ± centered front-back but watching the prongs on the input jacks. Avoiding backside traces, I drill 4 holes to evenly distribute the 'table legs' in empty areas of the board and chassis. Pre-existing holes may not be in those places.

I assume you're using a backing board? I clamp that behind the board and drill through both at the same time; then I use the backing board as a drilling jig, clamped or very securely taped to the chassis. Since it's easier to drill the chassis from the outside, I make sure to mount it with the eyelet-facing side lying on the steel. Make sense?

 

[prsman1981]

Question time. Are the yellow caps polarized? Layout indicates they should be. But I see no markings.

Edit: Been sick all week. My brain didn't put 2 + 2 together with the size of the cap. Just saw a black line on the layout and thought oh those must be polarized. (Backs away slowly from things that require thought until no longer sick)

 

[prsman1981]

Question time. Are the yellow caps polarized? Layout indicates they should be. But I see no markings.

Whoops. Film right? .22uf. Probably not polarized.