My First Amp... Help needed on ground.

[code_m]

Hi, I have attempted to build a Fender CHAMP AMP 5C1 from nothing but pure parts. To say the least, I did not have enough knowledge and messed it up pretty bad.

I have all new caps and resistors, and a few other essential parts so that I can start from scratch.

So now I have a few questions before starting over...
1. . What parts do you use to literally connect components to the ground?
. . Also, do all grounds on the schematic get connected to the same place and then that connected to the ground?

----A picture would be helpful! ... I read about a "ground star" somewhere, but it wasn't very clear.

2 . . What's the reason for the short switch on "input 1" ?

3 . . Easy way to test those expensive transformers?

----link would do fine.

Schematic: http://www.drtube.com/schematics/fen...-5c1-schem.gif

Layout: http://www.drtube.com/schematics/fen...5c1-layout.gif

Thanks for any help!

[tubeswell]

You ground various parts of the circuit to provide a return path to ground potential. This can be done in various ways. The way that works for me is a split ground.

For a split ground, you attach a separate wire to each of; the ground side of the 5M pre-amp grid load resistor, the pre-amp tube cathode , the ground side of the pre-amp screen bypass cap, and the ground lug of the volume pot, the ground side of the pre-amp filter cap ground. Then you run the other ends of these wires to the input jack ground.

Then you attach a spearate wire to each of; the ground side of the output tube cathode resistor/and bypass cap, the ground side of the reservoir filter cap and the ground side of the next filter cap, and attach the other ends of these wires to one of the Pt bolts with solder lugs, along with the PT heater CT, the PT HT CT, and the AC mains ground.

The switch on the input socket is a grounding switch to divert the signal to ground when a plug is not inserted. This stops the signal wire at the grid of the pre-amp tube from picking up stray RF when there is no guitar cable plugged in.

PS and if you are using a proper grounded (3-wire) power supply, then you should leave the death cap out (the .05uF 600V cap shown next to the fuse on the Fender schem) - including it will only make matters worse.

[cminor9]

You'll see two kinds of ground recommended, star grounding and buss grounding. There is some crossover between the two, many designs are compromises, and many people will partially implement star grounding. Basically the differences are:

Star: take all grounds to a common point and ground to the chassis. Earth ground gets its own ground point. All grounds leading to a common point give star grounding its name. http://www.aikenamps.com/StarGround.html

Buss: Take all preamp grounds, run them to a buss (just a wire) that is connected to the tone stack and input jacks and is then bolted to ground. Ground power amp, phase inverter, and earth ground elsewhere (usually to PT lug). This is essentially what tubeswell described above. http://www.el34world.com/charts/grounds.htm

Some prefer buss grounding. Some prefer star grounding. Whatever you use, make sure you read up on pros and cons of both. My very limited experience says that either grounding scheme can yield great results. I find that buss grounding leads to a neater chassis because with star grounding you often have lots of ground wires everywhere. And a neat chassis layout *does* make a difference.

Many very well known vendors (Fender? Marshall?) use a buss layout. Many well known vendors also use star grounding.

Learn which is best and make your own decision. I have tried both schemes in the same amp. I like buss grounding best because it's neater.

Sorry that doesn't help much, but it's somewhat of a subjective issue. Grounding is more important than you might have originally thought. I'd spend some time researching them.

As for preserving your power transformers, I'd real Paul Ruby's excellent article on your amp's first power up: http://www.paulrubyamps.com/info.html#FirstPowerUp. If you follow that, it's unlikely that you'll toast your trannies.

[code_m]

Thanks..

Thanks for the replies... I'll try to read up.

I really need a visual, I did read some on star ground on my last build, not sure if I did it right or not, seeing as how I messed up my caps and I already tore apart the amp.

I am worried I've already ruined the Power Transformer.

I'll post more later.

[cminor9]

Here is a picture of my amp's guts (it's a 5E3 head). It's not the best photo, since it's from my phone. It's the best I can give you for now.

The bare wire that you see running along the pots is my grounding buss. It's soldered to the back of those pots. The pots connect to it, then the grounds from the preamp, then the input jacks, and to the right of the jacks it bolts to chassis.

See those brown wires running from the board to the transformer? Those are grounds from the phase inverter (which you do not have to worry about on the 5F1) and power section. Those go to the transformer lugs.

Someone may jump in here and critique my wiring (it's my first amp), but the amp is quiet.

In case you get any ideas, I put the guitar cable in there going from the inputs and tone stack to the board as sort of an experiment to see if they quieted some hum I used to have. Going to remove them someday, since they clutter the amp.

[cminor9]

Sorry, forgot to upload that pic.

[code_m]

That's helps a good deal....

but since I only have a switched volume ... where do I put the buss wire?

also... that article made some sense... but, Do you use two separate grounds? one for the power and tubes, and then one for output and volume? They almost made it sound like there should be a separate ground for the input, the volume, the output, and the rest of the amp.... how do you make it so that it completes the circuit?

... This might be a bad thing, but I do not plan on using any sort of board, my tube socket pins are plenty long.

My box is a black coated steel 10x12x2.... most usable size I found.

[hr]thanks for all the help again... I'm sure that you understand. I would really like to avoid wasting more money on this project, it's already 3 times higher than expected.

[cminor9]

With just one pot, solder it to the back of the pot. You'll need a good deal of heat.

The grounds run to chassis at a few points. Remember, the chassis is a ground, too. One point...I have used this on aluminum chassis only. Never on steel. Steel is not as good of a conductor. On the other hand, this is basically how fender grounded their amps and they used steel chassis too.

The basic idea with ground is to prevent what you can think of as being "large" grounds (high voltage/current) from interfering with "small" grounds. Second, you need to prevent ground loops, which are caused when there is a voltage differential between various ground points. Buss grounding seems to put the first thing I mentioned as most important (keep large and small grounds apart), and star grounding seems to prioritize the second (eliminate ground loops). The reason why I am not a huge proponent of star grounds is that 1) Fender and Marshall have used buss type grounds for years (or some variation thereof, I have never actually seen a buss wire in a Fender, but same concept from what I have seen. perhaps some of the real old timers here can back me up or refute me) , and 2) the chassis doesn't have all that much resistance. So voltage differentials between various points on the chassis should, in theory, not be significant.

The idea of grounds not interfering with one another is kind of the idea behind buss grounding. Preamps, tone stack, and inputs can get grounded together (to the buss, which is then bolted to chassis). These are pretty "small". Grounds from the phase inverter and power amps could carry a lot more electricity. Generally, the farther you move to the left of a traditional Fender layout, the more signal voltage (since the amplifier *is* upping the voltage as it goes). So you want these "large" grounds away from the preamp grounds. So run these to the PT lugs. That's basically what the Hoffman site tells you to do, though I will admit it is a bit unclear the first time.

Not sure what the length of tube sockets has to do with the board (or lack thereof). Maybe if you can explain what you mean I can try to help.

Hope that helps. I understand what you mean, on my first build I wasted SO much cash! You learn, though.

[tubeswell]

Here's my 5F2A layout diagram

the first amp I built .... the picture is derived from many layout diagrams I'd seen around (but perhaps not as inspiring to look at as some )

[tubeswell]

5C1 gutshot

Original 5C1 gut shot (I believe)

(Courtesy of Mandopicker back in Jan this year - cheers buddy )

[code_m]

Ok.... thanks A TON!

well, that's definitely simplifies things (heh)... that picture has the main caps grounding to the chassis. I'll have to grind off my black coating and then check for resistance, but I think it will work.

I'll have to double check some tube stats, if I remember the 6SJ7 tube runs much higher than the 12AX7.

I'll have my father and grandfather help me out some on this now that I get it :-) ...

When I was talking about the tube sockets I was referring to the length of the solder pins.

And knowing that I could very well be working with damaged Transformers, what would be some thing to look out for?

[code_m]

PS and if you are using a proper grounded (3-wire) power supply, then you should leave the death cap out (the .05uF 600V cap shown next to the fuse on the Fender schem) - including it will only make matters worse.

I know I should have asked a while ago, but I assume I still run a wire back to the same spot as the cap is connected to in the schematic?

And because the main buss will be on the box itself, do I put the safety ground on the end of the buss, or just near it?

Other than that and my transformers I feel a lot better now, I understand quite a bit more.... I just hope I don't mess it up.

[tubeswell]

I know I should have asked a while ago, but I assume I still run a wire back to the same spot as the cap is connected to in the schematic?

And because the main buss will be on the box itself, do I put the safety ground on the end of the buss, or just near it?

Other than that and my transformers I feel a lot better now, I understand quite a bit more.... I just hope I don't mess it up.

You leave the death cap out altogether. Do Not run any wire from the active or neutral Mains A/C to the ground.

Attach the Mains AC ground wire directly to the chassis (one of the PT bolts makes a handy attachment if you solder a ring tab onto the end of it that will fit over the PT bolt.) run the other amp grounds to this same bolt (except for the pre-amp grounds - you want to keep them separately grounded together at the other end of the chassis - say at the input socket ground lug)

[Enzo]

Actually, tubeswell, in the USA anyway, the mains ground wire to chassis is supposed to have its own ground lug, not shared by other grounding wires.

[code_m]

... this is what confuses me.

What tubeswell is saying would not complete the circuit... right?

I think for my application, since all parts are grounded to the box, then I should use the cap to complete the circuit, and put the safety near the main buss, but not on it.

the last photo tubeswell linked to is what I'm pretty much am gonna do. only two major differences, I am doing an "upright" style head, so all tubes and transformers are above the box, and all resistors and caps are inside. The other is that I am using a safety ground.