Going in loops about grounds

[loudthud]

The red wire with a yellow stripe is typically the HV winding CT. The heater winding CT is usually green with a yellow stripe. Usually if a winding is one color, the CT will be the same color with a yellow or possibly white stripe. The 5V winding is usually yellow. Somethimes it will have a CT but a yellow wire with a yellow stripe doesn't make sense, Hammond uses a black stripe. (don't ground that one if used for a rectifier tube!)

[mbratch]

Ah.... thanks loudthud. I appreciate that insight. I do now recall that there were two striped wires when I worked on my vintage BF fender and both were grounded. But in my later SF amp, just one was. The PT I have in my kit doesn't have the 5V CT evidently.

[mbratch]

OK, here's what I am thinking for my grounding given that I don't have a brass plate.

I'm going to run a 14 gauge copper wire in back of the 3 pots and then attach to the chassis somewhere near the jacks (probably solder it there). The grounds from the pre-amp cathodes and the input jacks will attach to that ground wire at the nearest point for those items. The ground connections for the pots themselves will attach there as well (or perhaps to the back of the pots, like the old Fenders?).

The grounds from the dual-100ohm "virtual center tap", first two large filter caps (from the power amp section), and power tube cathode circuit will all "star" at the cathode circuit ground on the eyelet board. From there I'll run a ground wire over to the nearest lug on the PT. The HV CT will also be attached to this same lug.

The output jack will have the black ground wire from the OT attached to it.

The AC ground wire will attach to a lug on the PT mount (different from the one above).

I think this is basically the grounding scheme suggested by Hoffman.

Does this sound OK?

[stingray_65]

in my limited experience Ive found the 5E3 is not a very hummy amp no mater which grounding scheme you use.

each grounding scheme seems to have it's own sort of rules, do's and don'ts so try not to mix them

I can say from personal experience on my 5E3 build when connecting the twisted heater wires to the 12XX7's and then the 6V6's, make sure the same wires go to the same pins. use 2 different color wires or one with a stripe to make it easy on yourself.

this isn't nescassary on a single end amp like a tweed princeton

other than the making sure the heater wires land at the same pins, I've found I get most of my "hum" from the input jacks.

when I wired my 5E3 I followed the Fender layout faithfully.
the noise I did have was seriously reduced when I ran a shielded cable from the input to the tag board.
I was careful to attach the sheild at the jack .but you should only attach one end of the sheild to ground.
my noise went away completly when I replaced the cheap jacks with some switcraft 12A's. it doesn't pay to skimp here, it is an important connection.

nowadays I wire my inputs by laying out my input holes 7/8" - 15/16" apart and turn the jacks till the ground lugs face each other then bend those tabs toward each other and solder them together. I mount the 1 meg and 68K resistors to them so that only one signal wire per input pair is needed, and I land the directly on the tube socket.

If you do choose to assemble the inputs in that manor, it is important that you solder the inputs together when they are mounted securely in thier holes, or I will guarentee they wont fit if you solder them on your bench first the try and fit them.

[mbratch]

Thanks a whole lot. That's helpful.

Come to think of it, after looking at as many 5E3 build pics as I could find, they seem to use all manner of grounding schemes and nobody has complained.

[Enzo]

STingray opens with the point I would make as well. Let me say it a different way. Grounding, like so many other things, is a part of a whole amp, not a thing unto itself. SO it matters where and into what your grounding scheme is placed. The 5E3 is not a high gain amp, so there is less problem with hum than there could have been.

REducing hum is about keeping power supply ripple and hum currents away from the signal path. Tubeswell mentioned microbounces in the ground level. That is a good way to think of it. The 5E3 is relatively quiet, since there is not a lot going on with potential ripple currents in the chassis out of the basic power supply area. SO the brass plate or the pot cover bus can work well there. On some other amp it might not be the best choice.