Grounded Power Cord for B-15NC

[undertow1]

Many apologies if this has already covered.

Is replacing my two-pronged cord with a three pronged version as simple as:

1) Match & solder white and black legs of new cord to existing locations on amplifer ground switch (middle switch);

2) Connect green (ground) leg of new cord to amplifier chassis?

Thanks everyone.

MH

[Rick Auricchio]

If the amp has a ground-flip switch, you should disconnect that from the circuit.

[undertow1]

Yeah, I WAS wondering about that. Thanks.

[Rick Auricchio]

Typically, that switch will connect the power line to the chassis through a small capacitor. If you run the new power wires to the circuit "after" the switch, eliminating the switch from the circuit, you needn't worry about the capacitor. It will only connect the chassis to the switch, which goes nowhere.

[undertow1]

Tried to take a picture of the wiring with the laptop cam, but failed to get anything good.
However, what you describe seems to be the way the amp is wired up now.

To confirm, here's how mine is wired:

White Power Wire is soldered to the bottom leg of the Ground Switch. Another short black wire runs from this leg up through the chassis. Looks like it goes up to the transformer on that (the right) side of the amp.

Black Power Wire is soldered to the top leg of the Ground Switch. Another short black wire runs from this leg to the bottom leg of the Power Switch.

The middle leg of the Ground Switch has a short black wire that runs over to a yellow cap ON the circuit board. (cap specs: WMF 655, .05 MFD., 600 VDC, CDE +/- 10%).

So, if I solder the white and black wires of the replacement power cord to the repspective black wires that I'd be removing from the ground switch AND I connect/solder the new green ground wire to the chassis, taking the cap out of the circuit, that would be OK?

How about just connecting the new green wire to the capacitor, to exactly emulate the existing wiring? Not recommended?

Thanks heaps. What did we do before the internet, call people on the phone and stuff?
And where's all the computer chips in this amp?

[undertow1]

PS - man, I've been using this amp since 1993, and just noticed that one transformer tower is taller than the other. Signed, Mr. Oblivious.

[JimmyM]

Official Ampeg Portaflex Club Part II

5th post down.