3 prong power cord

[keith moon]

 Well,I have gotten 0 replies about a master volume mod to my sceptre. Maybe that was a taboo subject-modifying a vintage SUNN amp. I believe I stated that I wasn't going to disfigure the amp in any way-just wanna' control the pre-amp. Well,here is another question. On the old amps the power cord is 2 prong. That could be disaterous. I have gotten a few tiny shocks as well,nothing major but annoying none the less. How difficult would it be to put a 3 prong power cable on this monster? Also what is involved and what gets grounded? Hopefully I will get some replies on this one. I love my amp to death and wouldn't ever harm it. My sceptre has a fantastic sound as I would imagine that all old SUNN tube amps do.
 
all my very best,

[TubeMan]

converting to a modern 3 lead cord is easy actually.

just remove the old 2 lead cord, noting where the black and wite wires are connected to. Then, solder the black and white wires of the 3 lead cord to those same connections. Last, connect the green (ground) lead to the chassis via a binding post.. you can use one thats already in your amp if there is one free.. or drill a small hole in the chassis and make one using a bolt and nut.

all done!

ps.. make sure you unplug and discharge the amp before you work on it!

[rumblethump]

Tubeman, if I perform this mod on my Sunn 2000S will it be ok to leave the polarity switch hooked up?  If the polarity is switched after this mod will it cause any problems?    I would add that I live in a very rural area with many building erected long before building codes so this is a real concern.  TIA

[Geoff]

When my tech guy did this mod, he left the polarity switch and death cap intact (stock).  I asked him why and he said there was no reason to remove them.    Anyway, I've had no ill-effects.  I would have put the cord in myself but he suggested I solder the safety ground to the chassis instead of just bolt it -- and I don't have a big enough iron to do that job, plus I'm naive and like to spend money unnecessarily .

[JoeArthur]

I'm confused here.  If a competent amp person installed a three prong cord on my amp and then told me I should solder it instead of bolting it like he did... he wouldn't be very competent... would he?

All that is necessary is a good ground connection with the (usually) green center prong wire to the chassis.  That can be obtained with a nut and bolt connection or soldering.

With the chassis grounded to the center prong, then the "death cap" doesn't make any difference - the chassis will always be connected to ground, so removing it is not strictly necessary.

Besides... if you ever play in a place without grounded wiring, then the proper polarity can still be obtained through the polarity switch.

[Geoff]

I must have misspoken here. Sorry. I took the amp to the tech because he would (and did) solder the safety ground to the chassis.  I was just going to put a crimp lug on it and fasten it to the chassis with an available nut & bolt or rivet.

[rumblethump]

Thanks for the help gang, I'm on my way to the hardware store to get a 3 prong cord.