To Ground or Not to Ground -

[Bradbrews]

I recently finished rebuilding/modding some Dynaco MKIII's and have been looking at those old, small, 2 prong electric cords and wondering if they are in good enough shape to keep. After measuring all the high voltages on the B+ under that steel chassis, combined with the old, hard, transformer wire, I think that a grounded 3 prong plug would be the safer way to go. I know that the old way was to ground the chassis through the preamp. However, the set up I've got now doesn't have the preamp grounded back to earth either. This means that if I did have a short to the chassis, it just might sit there making both the amp and preamp hot - with possibly B+ voltage levels

On the other hand I would hate to suddenly have ground loop problems and need to find some way to lift the signal to stop them.
So - what do you do on your gear?

 

[primosounds]

If you are trying to get your amps as stock as possible then the original power cord is required. Guys that crave originality knock down non stock power cords. If this is not an issue then a 3 prong cord grounding the chassis is definitely safer. Don't leave out the x1y2 safety caps across the line and to ground. If i am not mistaken that method of AC power entry also passes code.

 

[gadget73]

I've grounded stuff and had no hum, and not grounded them and had no death. My pair of mono amps have one grounded and one not. Not because I have some master plan, but because one had a chopped off cord and the only one I had handy that fit the strain relief was a grounded one. I had only one, so the other one runs it's original non-grounded cord. I have been meaning to do something about that for about 2 years now but I'm pretty terrible about my own to-do list.

If you want to run a grounded cord but are concerned about the possibility of a ground loop hum, there is a fairly easy way around that. Instead of landing the ground direct to chassis, land it on a terminal strip next to a terminal that ties to chassis. Install a jumper between those terminals. If you have a problem, simply cut the jumper to take the ground out of the mix if needed.

 

[Bradbrews]

I'm not after originality on these. I removed the can caps, and installed Triode boards. I could add x1y2 caps, I don't have any in there now, but why? Line goes into the power transformer windings. Those won't pass any high frequencies with their high inductance, and the secondaries have lots of filtering, even if it did. Do you recommend them just because it can't hurt, or am I missing something? Aside from their name they don't seem to add any safety to the amp.

 

[GregBilodeau]

They are called safety caps not because they make anything safe but because if they have an internal issue they will fail safe. The old paper caps could fail with a short circuit which could energize the chassis with 120 volts. These are supposed to always fail open or they have what's referred to as being able to self heal an internal fault.
They will help with line noise issues if that is a problem in your area.

Gregb

 

[peterh]

I recently finished rebuilding/modding some Dynaco MKIII's and have been looking at those old, small, 2 prong electric cords and wondering if they are in good enough shape to keep. After measuring all the high voltages on the B+ under that steel chassis, combined with the old, hard, transformer wire, I think that a grounded 3 prong plug would be the safer way to go. I know that the old way was to ground the chassis through the preamp. However, the set up I've got now doesn't have the preamp grounded back to earth either. This means that if I did have a short to the chassis, it just might sit there making both the amp and preamp hot - with possibly B+ voltage levels

On the other hand I would hate to suddenly have ground loop problems and need to find some way to lift the signal to stop them.
So - what do you do on your gear?

Ground. Everytime. If hum occurs you have other problems, such as ungrounded pre or DC connection to
a cable-tv antenna.

As for replacing power cords ; installing an IEC inlet will assure that you always have a power cord in good shape.

 

[gadget73]

I'd be more inclined to install IEC cords if I had the knockout punch for them. They're not cheap though. I do have a set of square punches, I should experiment with those sometime to see if I can make a rectangle hole with them.

 

[larryderouin]

Gadget: I put an IEC in my 1000A. The original cord hole, and the Aux pwr outlet were sacrificed for this. Drew out the hole on the chassis and used a dremel with the H.D. Cutting wheel then a grinding stone to clean up the edges. The IEC was part of a Computer P.S. that had the X1/Y2 circuit on a board. It fit quite well and haven't had a problem since. Find an old Computer Power supply and yank the IEC plug, and the Transistor heatsinks.

 

[crispycircuit]

When nothing works- try a few cheater adaptors- magic!

 

[Palustris]

Ground. Everytime. If hum occurs you have other problems, such as ungrounded pre or DC connection to
a cable-tv antenna.

OK, I am getting didactic I know, but there should no longer be any question about this: for best performance and safety use a three prong power cord and ground the chassis.

 

[crispycircuit]

This debate will live on forever....

 

[gadget73]

Truth, which is why I'm inconsistent with my own gear. Whenever I notice a difference in how they act, I'll get back to you.

 

[peterh]

This debate will live on forever....

The non-grounded owners will die sooner Evolution favors grounded units.

 

[Tubeglowpio]

I'd be more inclined to install IEC cords if I had the knockout punch for them. They're not cheap though. I do have a set of square punches, I should experiment with those sometime to see if I can make a rectangle hole with them.

I would love an iec punch as well, but drilling a hole and using a nibbler gets the job done pretty good if you take your time, even better if you have a square punch.

 

[triode17]

I'd be more inclined to install IEC cords if I had the knockout punch for them. They're not cheap though. I do have a set of square punches, I should experiment with those sometime to see if I can make a rectangle hole with them.

Is there an punch for an IEC connector? I have been looking for one. I asked Greenlee and they didn't seem to know what i was talking about. Strange isn't it?

 

[triode17]

My first set up was a Dyna ST-70 and PAS3x. Upon rebuilding them, I Earth grounded each chassis for safety. There's no hum. Since then, all my rebuilt HiFi tube gear is Earthed. Just don't cross it up with a Cable TV ground, as they are often located away from the power ground.

 

[Tubeglowpio]

Is there an punch for an IEC connector? I have been looking for one. I asked Greenlee and they didn't seem to know what i was talking about. Strange isn't it?

I swear Greenlee was the only one who carried them? They go for at least a few hundred bucks.

 

[gadget73]

It may not be sold specifically for IEC sockets but Greenlee makes rectangle knockouts. They make a 22x30mm one that sounds like it would work.