My 5E3 Grounding Scheme - could someone offer some advice?

[deuce42]

Hi guys

This is my first post here and I look forward to learning a lot from the knowledge you guys have.

Could someone take a look at my wiring for my 5E3 build in the attached picture. I am getting terrible hum and have searched as many threads as I can to find the problem with my grounding scheme but the hum still remains.

I am sure there are many ways to wire this circuit in a much better way than I have done but would be so grateful for some advice as to what I've done wrong.

Thanks

[cbass]

The grounds for the preamp should be on the other side of the chassis.Like near the input jack.Lose the slip on connectors.Heater wires look to be awful close to the wires carrying signal.

[cbass]

Cut your buss bar between cap "B" and "c"and connect Cap "C" ground to your bus bar and connect the buss bar to ground on the other side of the chassis near the input.You definately want to move the ground from the treble pot to your buss bar.

[cbass]

Oh. and redo heater wires towards the back of the chassis keeping them away from other wires

[Structo]

What is the deal with the output transformer secondary?

Isn't there a ground wire from the transformer itself?

[Phil_S]

I'm sure Cbass is giving good advice on the ground buss. I've seen many give this advice, many pictures of quiet amps done this way, and I am convinced that it is good advice. It's just that I was taught differently and what I do also works. I run my ground buss the way you did it. Because of this, I don't believe it is your problem and I'd hold off on reworking it.

Your heater wiring, on the other hand, looks like a problem to me and you already have good advice on what to do, so I won't repeat, but will build on it. Put a pair of wires in your drill chuck and use that to get a nice even and tight twist to it. It will shrink to maybe 60% it's original length. Use that instead of what you've got. I'd discard the used heater wire or put it on the scrap pile for possible salvage. Run the brown pair from the PT on the other side of the rectifier socket and keep the wires away from any other wires going to the first socket.

I think you've got the green wire from the OT too close to the yellow wire on the next socket over. Try to reposition it.

After you rework the heaters, if you still have the hum, that, in my view, it the time to rework the ground buss.

Change one thing at a time and check the result. Otherwise, you won't learn what produces a result and what doesn't.

+1 on losing the spade connectors for chassis ground. You NEVER want the ground connection to come loose. Make it permanent.

I'd separate the heater artificial CT from the IEC ground. Joining these is a no-no in my book and in general. Essentially, you've joined a PT secondary directly to the mains inlet. Don't do this. Find someplace else for the heater CT.

[M Fowler]

Form now just add a 100 ohm resister off each filament wire to create an artificial center tap as you do not have a 6.3v center tap.

Mark

[deuce42]

Ok thanks guys for all your help.

I will try the heater rewiring as you say Phil_S. And I will move the green output wire away from the next tube. I'll also redo the brown fillament wires so they are not near other wires or near the rectifier.

Cbass- thanks for your advice. After re-doing the filament wires, I will try the group buss recofiguration as you suggest as it's good for me to learn and experiment.

Structo - the output transformer only has one output wire as the second one came soldered to the chassis of the transoformer itself - came like that from Magnetic Components.

MFowler - aren't the two resistors on the pilot light supposed to be the centre tap for the filament?

Thanks for all your assistance guys, I am very appreciative.

[tictac]

Your 100 ohm resistors are correct but your wire color coding isnt so great... I mean red for HV DC and for Ground?

When your building a device that has voltages inside that can kill you the best policy is to follow conventional color coding and not just go... "Oh crap I ran out of green (or black) wire, hey but I've got all this red, that'll do..."

At the very least the high voltage and grounds should not be the same! If you want to use purple, pink, and lemon yellow for everything else go for it but in my opinion sticking to conventional wiring schem may save your life or the life of someone else poking around inside your amp one day....

Just a thought...

One more thing... Are you absolutely sure your OT wiring is correct? Usually the primary leads connected to the plates are brown and blue, you may want to double check that; also you dont want the OT secondary to be grounded at the same place as your B+ supply... It should be at the same ground node you're using for the PI.

TT

[M Fowler]

I missed the pilot light Sorry, yes you already have that done.

Mark

[xtian]

In my (short) experience, BAD cases of hum are not the fault of suboptimal grounding schemes, it's something more obvious.

You can help isolate the issue by pulling tubes. First pull V1. Still humming? Pull the PI. Still humming? If yes, you can isolate the power tubes and solve the issue there.

[Structo]

Gottcha on the OT.

Just to expand on TicTac's comments.

We should all strive to build the best tube amp we can and as safe as possible.

None of us will live forever and these amps will live on.

You might even sell one to a friend or acquaintance so safety is paramount.

Your IEC connector needs attention.

Address the color coding.

The middle ground connector should have a short green wire of at least 18 gauge and it should be fastened to it's own screw and nut right below the connector. Make sure chassis is scraped down to metal. Use a lock washer or lock nut.

Be sure that the hot wire of the AC supply goes to the fuse first, then to the switch.
You want the fuse to protect the chassis from everything down stream.

Use green or black for ground wires, typically green is for AC ground and black is for DC ground.

Don't use red wire for the artificial heater center tap from the two 100R resistors.
Those resistors can be placed right at the socket and to a ground lug on a socket mounting screw.


Don't use yellow for high voltage DC to standby switch, use red.

Run your heater wires overhead of the sockets, make right angle bends down to the sockets.
This will reduce 60Hz hum.

We aren't picking on you, just trying to keep things quiet and safe.

[M Fowler]

BLACK - grounds, grounded elements, returns
BROWN - heaters/filaments, off ground
RED - power supply B+
ORANGE - screen grids (and base 2 of transistors)
YELLOW - cathodes (and transistor emitters)
GREEN - control grids, diode plates (and base 1 of transistors)
BLUE - plates (and transistor collectors)
VIOLET - power supply, minus leads
GRAY - AC power line leads
WHITE - bias supply, B or C minus, AGC

[xtian]

BLACK - grounds, grounded elements, returns
BROWN - heaters/filaments, off ground
...

Nice, Mark. I just printed and affixed to my amp-build book.

[deuce42]

Ok guys I take your point and am going to rewire according to Mark's colour code scheme. I appreciate your point about others using the amp one day.

Will post back a new picture.

Thanks once again.