5E3 grounding

[macdillard]

What type of grounding system is recommended for a 5E3? Star, Hoffman, buss, other? I have just finished my 5E3 except for the grounding. I am using elevated DC on the heater leads (100 ohm resistors for CT back to the power tube bias cap) but am kinda wishy washy on what grounding scheme to use. Right now I have it laid out for Hoffman's scheme as found on EL34 site..I know lots prefer star grounding..What is generally recommended for a 5E3...Thanks

[dai h.]

starring and bussing are just ways of connecting points. They aren't correct in and of themselves (i.e. star or bus something the wrong way and the result will be poor). Grounding at the most basic level is about current flow in the grounds and being concious of what, where, how much and wiring accordingly. If you don't feel like learning the theory (which I guess is okay if you just want to get an amp up and running), I would suggest copying a grounding scheme that is 100% known and confirmed to work correctly (no hum, buzzes, instability, etc.). There are different pros and cons about the different ways of hooking the grounds up. For example, Hoffman apparently has found Fenders with the brass plate in Florida climates corroding (leading to poor contact) and causing probs. The one where a gigantic multitude of wires goes to one point is pretty time consuming, inefficient (and not really necessary). If you follow vintage exact schemes where there are lots of chassis connections, this can make it a pain to convert to a scheme where the circuit ground is raised a bit (to deal with ground loop/interconnectivity probs with other equip.) and so on.

[Bruce / Mission Amps]

What type of grounding system is recommended for a 5E3? Star, Hoffman, buss, other? I have just finished my 5E3 except for the grounding. I am using elevated DC on the heater leads (100 ohm resistors for CT back to the power tube bias cap) but am kinda wishy washy on what grounding scheme to use. Right now I have it laid out for Hoffman's scheme as found on EL34 site..I know lots prefer star grounding..What is generally recommended for a 5E3...Thanks

The brass plate is the best. It is a giant star ground and if you do it right, (solder all the gnd wires to the brass plate), you have no chassis point that is a ground.
In other words you never use the chassis as a ground point for anything except the green power cord earth ground.
By the way.. I've worked on hundreds of vintage Fender amps, sent to me from all over the USA, Gulf Coast and Florida included... and have NEVER seen
even a mildly corroded brass plate in a chassis.
Does that mean Hoffman or others have not? No, but I think most of that is a bit over done and Net driven hype to sell products.
The brass plate with proper grounds is king in most simple amps.

[dai h.]

to my thinking the brass plate would be equivalent to putting all the points on the brass plate to a central point on the chassis using a bunch of separate lugs. Might look different but basically the same thing (think of how it would look if that central point expanded 360 degs. outward like a blob--well a rectangular sort of blob, lol). My understanding is that brass is lower in conductivity compared to copper, however, the plate in area is really big so that should help to keep potential differences small (low resistance, impedance).

[loudthud]

I saw one of Bruce's layouts and he had everything connected to the brass plate EXCEPT the HV center tap. It went directly to the minus side of the first filter cap. I think this is a much better idea than connecting that wire to the brass plate.

I don't like Hoffman's scheme but it seems to work well enough for many people. I prefer O'Connor's method but I hate those darned washers and plastic jacks.

[macdillard]

Thanks for the replies. Not sure that all were what I was looking for except for Bruce's recommendation to use the brass plate..I have never tried that. Any amp board you go to will have discussions about grounding schemes. Some favor one over the other for various reasons. I was looking for a recommendation of the one that best fits the 5E3. Probably got that from Bruce. Now dai h, I do simply want to get this amp up and running. I build guitar amps as a hobby because I found that, after building the first one, I really enjoyed doing it and they are not for sell. I don't even play guitar. I give them all to my Son who plays. Some 40 years ago I by some miracle ended up with a degree in EE. That was in the days when vacuum tube design theory was still taught. So I do understand grounding. I could do the load lines, divider circuits, frequency calcs. resistor sizing, PS design, shoot the whole amp design if that was what I wanted..I simple build old classic amps from proven designs because I enjoy doing it. (Well not all classics, try a Melissa with its DC drive for a change if you like).

[HTH]

Las time I did an amp with any 'considered' grounding scheme was when I did my SLO100 clone. I read Randall Aiken's article on multiple star grounding and went with that.

If I remember rightly I had all the grounds from each correcponding power supply node connected together and bolted to the chassis as a ground point.

I also lifted the CT on the heater winding, used a 100ohm trimpot to get the least hum and put around 40v into the output valve cathodes. This totally removed the hum levels.

I was expecting a fair degree of hum with such a high-gain design, but the grounding scheme I used must have worked out as it was quieter than other simpler low-gain amps I've made.

[Bruce / Mission Amps]

I saw one of Bruce's layouts and he had everything connected to the brass plate EXCEPT the HV center tap. It went directly to the minus side of the first filter cap. I think this is a much better idea than connecting that wire to the brass plate. ...

But even at that, there still is a singular wire from the second filter cap's negative lead that also goes to the brass plate.
I just make sure the chassis is not used for any ground points and for the most part, the only hum I ever hear is just very low level "flux line" hum, probably leakage from the PT to the OT... another reason why all my 5E3 chassis have the 5E3 OT mounting holes punched in two different places... for that crazy studio cat that just can not stand that last 20mvac of hum on the speaker leads.

[Gee]

One of the big advantages of the brass plate is that you can assemble and pre wire the input jacks onto to the brass plate before fitting them to the chassis. This really makes the installation of the input jacks much easier.

[macdillard]

Bruce, You ever do the headphone trick for xformer location>

[macdillard]

Well, got the 5E3 up and running..Ended up using the Hoffman grounding scheme and elevated the heater voltage by about 29 vdc. It is very, very quiet. Kid will be home tomorrow and he will put it through its paces..Initially I plugged in the only guitar that the kid has left at the house. It has some pretty hot humbucker pickups..may have to do the humbucker mod that Bruce sells if the kid is going to play it with the humbuckers..Has anyone tried removing the 2nd stage cathode bypass cap?

[Bruce / Mission Amps]

Bruce, You ever do the headphone trick for xformer location>

Yes, but I use my O'scope, probe set to 1:1 and the vertical set to a very small milivolt ac scale... it's very sensitive to hum, noise or any changes on the speaker leads.
I just rotate the OT until there is a deep null and mark it on the chassis.
It turned out that when using my custom wound power and output trannys, there is a spot a little further away from the PT and between a 30 to 45 degree angle that is a null point.
For the last couple hundred 5E3 chassis, I had all of them punched with PEM nuts in the standard location and for that null spot too.
Not many would complain about the hum with it in the stock position because it is very low, so I don't mess with it unless someone is super anal and suffering from unrealistic, hum compulsive disorder.

[TD_Madden]

That's ME!

[MLC]

I just make sure the chassis is not used for any ground points and for the most part, the only hum I ever hear is just very low level "flux line" hum, probably leakage from the PT to the OT... another reason why all my 5E3 chassis have the 5E3 OT mounting holes punched in two different places... for that crazy studio cat that just can not stand that last 20mvac of hum on the speaker leads.

So Bruce, what would the "correct" mounting position be for the OT for lowest hum?
(both OT and PT being the standard issue 5E3 Kit versions)

thanks,
Mark

[Bruce / Mission Amps]

So Bruce, what would the "correct" mounting position be for the OT for lowest hum?
(both OT and PT being the standard issue 5E3 Kit versions)

thanks,
Mark

Correct is exactly as is but there is a slight improvement at around 30 to 45 degrees.