Got shocked BAD

[LeftyStrat]

I got hit with a shock off a particularly high voltage Marshall. I remember telling my wife "Marsha tried to kill me" because the amp had the last two L's broken off the logo.

The owner of the amp was in the room and tripped over the guitar cable and almost pulled the amp off my stand. I tried to grab it and it then grabbed me.

I now have a special anchored cable I use. And I'm a firm believer that "hand in a pocket" is safer than "hand behind your back."

[Structo]

That is a perfect example why when you hard wire the power cord to an amp, that you make the ground wire the longest of the three wires.

That way, when somebody trips over the power cord, even if the hot wire is pulled loose, the ground wire is still connected to the chassis, grounding the chassis so you don't end up with a hot chassis in your hands.

[TUBEDUDE]

Same goes for wiring A.C. plugs, the ground wire is the longest. (Assuming I'm not the only one left that doesn't use molded plugs).

[Cygnus X1]

Wonder if this ever was figured out.
I'm getting full B+3 VDC between circuit ground and the chassis on a new 5F1 Champ build.
That's 250VDC between the neg of the input jack and chassis.

Input jack is isolated.

Circuit is NOT grounded to the chassis.

Using a center tapped transformer with two 5407 diodes and a 500R dropping resistor.
Everything else looks normal.

Thoughts?

[Cygnus X1]

[img:800:462]http://img839.imageshack.us/img839/7328 ... mpgut1.jpg[/img]

[tictac]

1) There is no negative on the AC input; it's a hot and a neutral.
2) Looking at your photo, looks like you have the hot (black) and the neutral (white) reversed in wire color at the terminal strip; and so what part of the circuit are you reading voltage at?
3) Is your plug wired correctly?
4) Is your AC outlet wired correctly?
5) the wiring to the switch looks shabby and could cause noise problems; a twisted pair routed around the transformer end-bell would be better.

TT

[tictac]

Oh, 250 volt DC....

The neutral is actually an isolated ground so the reading you're getting shouldn't be a problem....

The important thing is that you have a solid ground connection from the AC ground to the chassis...

The stuff from my first post still applies as far as safety and good layout goes...

TT

[Cygnus X1]

Oh, 250 volt DC....

The neutral is actually an isolated ground so the reading you're getting shouldn't be a problem....

The important thing is that you have a solid ground connection from the AC ground to the chassis...

The stuff from my first post still applies as far as safety and good layout goes...

TT

Thanks.

Yes, didn't have room for the twist and shout on the PT primary so it is soldered to a riser strip to hold everything together.
What about grounding my Center Tap to chassis?

I didn't do that for some odd reason.
It's just tied in to the circuit as the negative reference for everything (except the chassis).

[Cygnus X1]

Attached a jumper between the center tap and the chassis.
No voltage between ground and chassis now, but it made bad popping noises and no sound went through.

Now what?
Tie the jacks to the chassis?

[Cygnus X1]

Guess I got ahead of myself.
After the popping, I removed the jumper between the CT and the chassis.

Now I'm getting nothing, apparently fried something?

At least it was pushing a signal before!
Now, just dead.

[tictac]

Normally a secondary with a center-tapped winding will have two red leads which is each end of the winding with a center-tap winding that is usually red/yellow or red/green. The red leads go to the rectifiers and the center-tap is grounded. So grounding the center-tap would not harm your amp.

Looking at your picture it looks like you have the red leads going to the diodes which is correct. Can't see your center-tap wire but if you don't ground the center-tap the amp won't work; some amps have the center-tap wired to a switch and use it as a standby switch.

You must grounded the output of another winding in your secondary. Did this PT have a negative bias winding? If you grounded that by mistake it would explain the popping and no output. Some bias windings are actually part of the B+ winding and shorting it to ground would fry part of the B+ as well.

It's good practice to always use an ohm-meter to check what windings are what before hooking them up... do you have a schematic of the finished amp?

[Cygnus X1]

Thanks tictac.
It does indeed have a bias tap.
No need and this oversized PT happens to provide just what I need.
They are sealed off.
I not only ohmed out the leads but I applied low voltage to make sure everything was sorted out.

I've had many successful builds but sometimes something really simple might bite us all in the proverbial donkey.
This is one.

I swear I've not grounded CT to chassis, but now I'm seeing full b+3 reference.
And by jumpering I think I cooked something to make it not work any longer.
Hate to think I popped the OT.
I already had it out and tested once thinking it was shorting to the chassis.
It was OK at that point.

[tictac]

If you're using a full wave rectifier setup which is what you are using then the CT must be grounded or the amp will not work; you'll be able to read some B+ but the amp will have no output...

If you were using a full wave bridge recitfier (4 diodes) then the CT would not be grounded...

You should draw a schematic of your amp or at least the power supply; it's really diffucult to troubleshoot without one... carefully drawing a schematic may even reveal the problem to you as you draw...

TT

[Cygnus X1]

Did it, now she's working.
Yes I fried that old output transformer along the way.

Put in another, cleaned things up, fine tuned and life is grand.
Finished pics:

[img:500:800]http://img835.imageshack.us/img835/5047/rca5f1back.jpg[/img]

[img:740:460]http://img109.imageshack.us/img109/7328 ... mpgut1.jpg[/img]


[/img]http://desmond.imageshack.us/Himg204/sc ... anding[img]

Appreciate all the help!

[Cygnus X1]

Arg.