Ampeg grounded power cord mod

[bware]

What is the proper way to install a grounded power cord in a 1960s Ampeg Reverberocket?

[Bruce / Mission Amps]

Get a three wire power cord. At least 18g SVT or SJT. I'm thinking 18g will be fine.
Strip the black insulation back about + four inches to separate the wires in the cord. More lead length can be a blessing when you realize the white wire isn't long enough or the black wire won't pull over to the fuse holder when the green wire is mounted to chassis ground. etc.
Strip back about a half inch on the white, green and black wires, and tin them with a little solder so they will be a little stiffer and take solder better when you mount them in their respective places.
Green is chassis ground, Black is 120v hot and white is the neutral wire.

Install a #10 grounding solder lug on the green wire of the new power cord.

Look to see where the old power cord is installed with respect to the fuse holder and the power transformer wire. Remove your old power cord.

If the bolt that holds the PT to the chassis is too short to use a nut to capture that solder lug on the new three wire power cord, drill a small 1/8" dia hole in the chassis near the power transformer. Careful, don't dill through and hit anything on the other side.
Clean/scrape/sand... the metal around the hole right down to bare shiny metal.
Use a 1/4" to 3/8" long #8 sheet metal screw to attach the green ground wire and solder lug to the chassis.
You install the new black hot wire wire of the cord to your fuse's center lug, the white neutral wire to the other side of the power transformer's primary winding return and eliminate the .047uF cap if you want.

This is important:
When dressing the actual power cord lead lengths (properly installed), try to keep the green wire (any colored chassis ground wire of the power cord) the absolute longest one so if the power cord starts pulling out and the black comes off the fuse holder, the chassis will still remain grounded!

Nothing much worse then having a live 120v@15amps power cord wire dancing around loose in your chassis with no ground!!
That is over 1,800 watts of power trying to find a place to go.
If the green wire is still connected to the chassis and the outlet is correctly grounded... when the black wire rips out touching the chassis, it will blow the main 120v house fuse or trip the circuit breaker and save your tail.
Ugly but you will be able to laugh about it.

Make sure you use a good chassis strain relief (that actually fits) to keep the power cord in place....

[hasserl]

Good detailed advice Bruce. I like the advice to keep the green wire the longest! Thanks.

[52 Bill]

Yes! Very good instructions.

Officially, isn't the ground lug supposed to have a separate attachment point?

[Bruce / Mission Amps]

Yes! Very good instructions.

Officially, isn't the ground lug supposed to have a separate attachment point?

Yes, technically and also, it supposed to marked with a schematic symbol for GROUND right on the chassis at that point.

[Enzo]

Green screw too?

isn't there a regulation either here or maybe Euro these days that anything with a permanenty attached powr cord must be able to hang by that power cord without it pulling out? This making detachable power cords oh so much more attractive.

[loudthud]

When I took a product through UL in the late 80's you were allowed to use an alternate pull test attaching a 25 pound weight to the power cord for IIRC 5 minutes. I had to spec a #16x3 power cord and the correct Heyco strain relief because the chassis of the product had the big size strain relief hole. All this for a product that used a 50 watt power supply but only consumed 20W.

[J Martin]

If you use an existing screw for grounding, You will need a #8 lug for the transformer screws or a #6 lug for the screws that hold the cap can in place. You should remove any existing lock washers if your ground lug is not the smooth type. I am glad to see mention of keeping the ground wire longer as few seem to pay attention to that. It is documented in the NEC, among other places.

[bware]

Ul B Ok

I made the mod. Although it probably wouldn't pass UL standards, it's safer than it was.