OT: Amp Grounding

[petemoore]

  Edited:
  I connected a 3 conductor power supply cord,
  Green is soldered to lug bolted to the chassis.
  Black is to what looks like would connect to the positiveside of the circuit.
  Neutral is going to where the old plug wire went, to many electrolytics - connections etc.
  There was noise but very distasteful hum. I shut her down.
  Wondering whether I should try it with neutral wire and greenground wire together.
  I have a two conductor main power supply cord, I'd like to put a 3 conductor on.
  Small Tube Amp [Zenith Ambassador, modded], needs ground work. For going just to a phono needle, ground isn't as necessary as going to other effect jacks and guitar.
  I'm pretty certain it can be done, but I'm not going to try it before feeling pretty confident about what I'm doing.
  Is there a page, [I've been looking around but haven't found anything related to this] that shows how this could be done?
  I know I can get shocked the way it is, when connecting other stuff, and I'm hesitant to use it. I think the ground problem is also the main contrubutor to the hum.

[niftydog]

Wondering whether I should try it with neutral wire and greenground wire together.

I don't beleive you should! The AC voltage is present between neutral and active - ground doesn't necessarily need to be there to complete the circuit, it's more a safety feature than anything else. However, the AC voltage is only sourced from the active, so you should be sure you have not transposed active and neutral.

Normally black is active, white is neutral and ground is green. For the Aussies out there, active is brown, neutral is blue and ground is green/yellow. Sometimes it goes active is red, neutral is black and ground is green. (personally, I think that last one makes the most sence, but it's the least common these days!)

To change a two pin plug to a three pin plug is simply a matter of wiring the new active and neutral to the same point as the old active and neutral. Then, the third wire - ground - simply connects to the metal chassis of the unit. Again, as I say, ground is just a safety, it often plays little or no part in the circuits operation.

[RedHouse]

Pete,

This a great forum, and no disrespect intended, but you really should consider coming over to AMPAGE and AX84 for these kinds of things.

http://www.firebottle.com/fireforum/fireBB.cgi?cfg=ga&enter=go

http://ax84.com/bbs/

amps can be quite different animals tha stompboxes, and you can leverage much more amp-related experience there.

[petemoore]

  I have a thread in at Ampage, and John Martin has just posted some good stuff, I'm going to try out...
 

[R.G.]

I have a two conductor main power supply cord, I'd like to put a 3 conductor on.

No problem.

1. Does this amp have a power transformer or is one of the transformerless ones? If it is a transformerless one, DO NOT PROCEED UNTIL YOU CAN INSTALL AN ISOLATION TRANSFORMER. The old two wire transformerless amps are death waiting for you in the box.

2. If it is a power transformer version; remove the old two wire cord and remove any connections to a "line reverse" switch. You can leave the switch in, just don't connect to it.
3. Install the 3-wire cord with strain relief. Wire the green or green/yellow safety ground to the chassis by connecting a crimped on ring terminal, and installing a screw through the chassis for the ground wire, and no other purpose. The stack on the screw should be (a) external toothed star washer (b) ground ring terminal (c) external toothed star washer (d) nut. Sand the chassis around the screw hole down to bare metal before installing the screw/stack. Leave the ground lead longer than the white/black wires so if someone pulls out the power cord, the powre lines open first.
4. Wire the black wire to (1) power line fuse holder (2) AC power switch (3) AC power indicator light, if it's run from the line (4) transformer primary lead.
5. Wire the white wire to the other power transformer lead and the free end of the AC power light if it's so equipped.

Do NOT put the AC switch and the fuse in opposite sides of the AC power line like many old amps.

Check your work for continuity to chassis and between AC power lines before you plug it back in. You may need to install another terminal strip for the new connections.

[petemoore]

  New Edit:
  RG is helping me figure this thing out over at Ampage, Thanks RG! A recent post make me feel a bit more confident, and I think I'll be able to access a tranny and wire it in there soon enough !!
  Here's the rantypost From before...I *would like to be able to access information from the AX84 site that seems to require login, which seems to be inaccessible to me, I've tried new accout, change password, login...all to no avail...I cant' figure out if I'm dummy or if it's just 'closed'...
  I can't get in or get much from ax84, sign in is not necessary, but seems to be.
  I find plent of 2 prong schematics...here's another:
  http://195.178.239.50/ax84/media/ax84_m152.pdf
  A McTube
  http://www.firebottle.com/ampage/schems/stpre.gif
  Silvertone doesn't show power supply section
  http://www.firebottle.com/ampage/schems/twdchmp.gif
  Tweed 2 pronger
  http://www.firebottle.com/ampage/schems/twdpwr50.gif
  2 prong power amp
  http://www.firebottle.com/ampage/schems/hpreg.gif
  Another without PS Section
  http://www.firebottle.com/ampage/schems/hwpre.gif
  Nothing useful here
  http://www.firebottle.com/ampage/schems/lyonhardt.gif
  Maybe useful, if I could sort it out, looks like more than I need, no specs or part #'s...uses rectifier
  http://www.firebottle.com/ampage/schems/mvp.gif
  another http://www.firebottle.com/ampage/schems/m2000a.gif
  Here's one...looks like more than I need, but has the third prong at least
  http://www.firebottle.com/ampage/schems/mb1pwr.gif
  No Part#'s or specs, I'd need to sort it out, don't know if this schematic is an optimal reference for what I'm trying to do...
  http://www.firebottle.com/ampage/schems/vxbpre.gif
  No Power supply shown
  I found a Bandmaster 2 prongster also
  Looking at the schematics I've looked at I'm not seeing a 3prong setup for power supply
  I'd like to know the specs for a suitable isolation transformer
  Wiring for the 3 prong cord and transformer
  Part # for the transformer...
  I've been searching a couple hours for a couple days...havne't really found any applicable info on how to go about the 3 prong power supply wiring.