Cap job - grounding ?

[hamfist]

Just put a full new load of electrolytics in my Wilsic Sound V-50, which is now pretty much modified to 2204 spec.
34 year old RS's out, new JJ's in. Simple job, two cans, 32x32 each. (a damn sight easier than my Selmer 100W PA, which needed 8 new cans - phew !!).

Amp sounds great (as it did before).

Thought I'd measure the B+ to see if it had changed noticeably.
V4 or 5, pin3 to chassis .......Zero volts !!!

Huh ....the amp is loud and proud. How is it doing this on zero volts ?

CHeck voltmeter - all is OK there.

Then it came to me, the Wilsic's entire grounding system was grounded to the chassis through the outer metal casings of the old RS caps. JJ caps have a plasticised outer, so no grounding to the chassis through the clamps was happening.

So my question is, do I now simply just ground the caps negative terminals to the chassis to replicate the old grounding scheme ? Seems to me like that should be the right thing to do. Just wanted to check first before I do anything stupid.

[bnwitt]

Where is the center tap of your power transformer's high voltage secondary grounded or do you have one? Where are the cathodes of your power tubes grounded? Your filter caps negative terminals should share the same ground as your cathodes

[hamfist]

Where is the center tap of your power transformer's high voltage secondary grounded or do you have one? Where are the cathodes of your power tubes grounded? Your filter caps negative terminals should share the same ground as your cathodes

The centre tap of the HT secondary of the PT, and the cathodes of the power tubes all ground along a central bus bar.

My understanding is that the entire amp's grounding scheme centres around this central bus bar, which is attached to the electrolytic caps negative terminals.
The old electrolytics that came out said "red +, black -, can negative" on them. I assume this means that the outer metal can is connected to the internal negative. the outer metal can then grounded the whole amp through the metal can clamp, which obviously screws into the chassis.

[bnwitt]

That would be correct (can is negative) For safety, I would ground everything to the central buss bar and then the buss bar to the chassis along with the power cord's ground wire. You do have a 3 wire grounded power cord right?

[hamfist]

That would be correct (can is negative) For safety, I would ground everything to the central buss bar and then the buss bar to the chassis along with the power cord's ground wire. You do have a 3 wire grounded power cord right?

Yep, 3 prong power cord. It's a good plan you've outlined, and is what I intend to do now.
THanks very much for your input.

[hamfist]

Just grounded the Buss bar to the chassis right next to the electrolytic caps. All is good now.

[bnwitt]

Glad to hear it.

[Dave Curtis, dB AudioTech]

Just grounded the Buss bar to the chassis right next to the electrolytic caps. All is good now.

FYI,

The ground wire from the AC supply should be bolted to a point near where it enters the chassis and should not rely solely on solder for a secure connection.

DC

[hamfist]

FYI,

The ground wire from the AC supply should be bolted to a point near where it enters the chassis and should not rely solely on solder for a secure connection.

DC

I've actually done two grounding points to the chassis. One with solder. The other is just wire clamped under a bolt and washer.
I think that at some point I will get a proper grounding post/lug and get a very permanent, and stable grounding point (on top of the ones I have already !).

[Dave Curtis, dB AudioTech]

I've actually done two grounding points to the chassis. One with solder. The other is just wire clamped under a bolt and washer.
I think that at some point I will get a proper grounding post/lug and get a very permanent, and stable grounding point (on top of the ones I have already !).

The signal ground can be soldered; that's OK. The equipment ground (from the AC cord) is the one that shouldn't be just soldered, as in the first pic. Fender often used a lug bolted to one of the PT mounting bolts and soldered the lug to the chassis as well as in pic #2.

[Bruce / Mission Amps]

The signal ground can be soldered; that's OK. The equipment ground (from the AC cord) is the one that shouldn't be just soldered, as in the first pic. Fender often used a lug bolted to one of the PT mounting bolts and soldered the lug to the chassis as well as in pic #2.

And that first picture with the soldered ground wire is additionally incorrect as the grounded wire needs to be the longest one of the three power cord wires so when or if you rip the power cord out of the chassis/strain relief, the ground wire is still attached to the chassis, keeping it Earth grounded.
That way if the hot black lead touches the chassis on on the way out... it blows your home/shop/club, mains circuit breaker or fuse, ....
saving the possibility of you waking up in a puddle of pee.

[hamfist]

And that first picture with the soldered ground wire is additionally incorrect as the grounded wire needs to be the longest one of the three power cord wires so when or if you rip the power cord out of the chassis/strain relief, the ground wire is still attached to the chassis, keeping it Earth grounded.
That way if the hot black lead touches the chassis on on the way out... it blows your home/shop/club, mains circuit breaker or fuse, ....
saving the possibility of you waking up in a puddle of pee.

Great safety tip. Something I woudn't have considered before !

[bnwitt]

Bruce,
I take it that is a UL requirement?

[Bruce / Mission Amps]

Bruce,
I take it that is a UL requirement?

That and that the chassis has to marked and stamped with a separate and real "Earth ground" point where no other connection can be made to that same spot. They are also supposed to be Hi-Pot tested at 1500v!!
It's really just a good safety practice when building portable electrical devices like this... , you know, where you're constantly schlepping the thing around from place to place and plugging or unplugging the power cord.
I'm sure this is why most modern amps have those easily lost, IEC plugs and removable power cords. Fortunately those cords are fairly universal.

[slidincharlie (Carlo P)]

The signal ground can be soldered; that's OK. The equipment ground (from the AC cord) is the one that shouldn't be just soldered, as in the first pic. Fender often used a lug bolted to one of the PT mounting bolts and soldered the lug to the chassis as well as in pic #2.

Two questions:
1) What's the reason for this (I mean, bolt plus solder)?
2) I have used in one or two occasions the mains ground lug/bolt on the PT also for grounding a filter cap. Is this bad?