Help removing Ampeg V4 death cap?

[EWaffle]

I have a 1974 V4 head that shocks me every now and then, usually when touching my guitar strings and touching another person who is touching their strings, or when touching my pedalboard. And it's a nasty shock too that really wakes you up. Anyway, recently my V4 stopped turning on and I ended up opening it even though it was just a blown fuse, and while I'm in here, I wanna look into removing the death cap. Not sure these regular shocks I get have anything to do with the death cap, but I figure I might as well do this now. I can't find any pictures of it online, but I think it might still be here. My 3 prong cable doesn't appear to be soldered to the chassis either. Can anyone tell me where to start with this? I'm comfortable working inside tube amps, I just don't know the specifics to get this job done.

I attached some images, is the death cap supposed to be that dark blue one?

[Leo_Gnardo]

is the death cap supposed to be that dark blue one?

Looks like that's it. Never saw that kind of cap used by Ampeg though. Maybe someone long ago pinched it from a Fender and exchanged it for the white ceramic cylinder type Ampeg usually used. Well, no matter, just clip it out.

Look carefully at the tie strip there behind the power & standby switches. You'll see one lug that's bolted to the chassis, a handy spot to solder your AC wire ground wire. Good luck and enjoy life all that much more without shocks.

[EWaffle]

Cool! Thanks. So the three prong power cable has a black, a white, and a green wire coming out of it, and I assume the green is ground. The green wire is already going to the lug that's bolted to the chassis, the same lug that one end of the death cap is connected to. So do I just snip the death cap away, no further mods or jumpers or anything needed?

[nevetslab]

Cool! Thanks. So the three prong power cable has a black, a white, and a green wire coming out of it, and I assume the green is ground. The green wire is already going to the lug that's bolted to the chassis, the same lug that one end of the death cap is connected to. So do I just snip the death cap away, no further mods or jumpers or anything needed?

You got it....cut that cap out, and the shock hazard is gone!

[g1]

I'm a little confused about where the green wire is going. It looks to me like it goes to an accessory socket. You say it goes to a lug bolted to the chassis. Is the AC plug intact?
If the green wire is connected to chassis, you should not be getting shocks, death cap or not. (unless the other guys amp is not grounded, in which case, I don't think removing death cap will help)
You need to find out why you are getting shocks, if you have a properly grounded 3 prong, the death cap is not the reason.

[EWaffle]

Yes the green goes to a lug on the accessory socket, but connected to that same lug is a white wire going to the tie strip lug that is connected to the chassis. Perhaps I should have mentioned that, but I figure it is going directly to ground with no interference.

So I cut the death cap, and I took a look at my non-functioning reverb tank while I was at it and found a tiny little wire that had broken, so now I have reverb for the first time as well!

Anyway, amp is back together with death cap cut out, and I'm noticing a good amount of hum. Not sure if it was there before, but I'm sure when I'm playing loud I won't be hearing it. Thanks for the help! Any idea if adjusting bias could help with hum? My hum balance pot doesn't change anything.

[Leo_Gnardo]

My hum balance pot doesn't change anything.

I find in lots of old amps with hum balance pots, there's been at least one instance where an output tube has shorted and wrecked the HB pot.

It would be a good idea to use an ohm meter to check continuity between your AC power plug and chassis. It's "supposed" to be made as you have observed, factory wiring has it going to the aux outlet then jumpered to chassis. However it's always a better solution to have the AC cable ground wire connected directly to chassis. Good as Ampeg's build was, it must have been a so called expedient solution, save time on the production line, to wire it up as they did. We can do better.

Good move on the reverb tank!

Back to the power cable. Sometimes you'll find in an old cable, one of the internal wires has become discontinuous, often within or right near a moulded plug, also near the chassis, both areas often subject to hard bending and a lot of force when someone yanks on the cable or trips over it. You'd know right away if it was one of the power lines, right? Not so obvious if it's the ground wire, you only find out when you get shocks. A few seconds with an ohm meter, you'll know if it's the cable or not.

[R.G.]

I feel this is getting you into possibly dangerous territory for you. Not knowing for sure with no question which wire color is which on your line cord is an indication that you're not yet familiar enough with AC line power wiring to be doing this. My saying this is not intended to be an insult, but rather a concern for your health.

On the AC line cord: the green or green/yellow wire is safety ground. The white wire is the neutral wire, which is connected to safety ground and earth-rod ground back at the breaker panel. The black wire is the line wire, and is where the 120Vac lives.

Three wire grounding: your amp is dangerously wired. I think it may have received an attempt at three wire grounding by someone who didn't understand three wire grounding. No one should put a three-wire cord on an amp and not connect the green wire to anything. That's like buying a pet rattlesnake: it's not automatically fatal, but you can get bitten unless you're very careful. The reasoning behind death caps even existing is that the chassis really needs to be tied to some kind of "Ground" to limit RF noise and hum. In the era of two-wire cords, the death cap and line reverse switch were developed to easily connect the neutral wire to the chassis through a capacitor that is small enough to let RF and noise through, but very little of the AC line 60Hz. This was always a trade-off - small caps don't bypass all the noise, and big caps let a trickle of AC through to give mild shocks. And if the cap fails, one position of the AC reverse switch is deadly when it connects the line to the chassis through the shorted cap. That's why it's called the death cap.

If you have a three wire cord, but a death cap setup, if the green wire is disconnected, your amp is pretending to be safety ground wired, but isn't. If the green wire is tied to the chassis, or the bare end touches the chassis, in 50% of the line reverse switch positions, the AC line is connected to the green wire ground by the death cap. That puts any AC line transients across the death cap, and may damage it more rapidly. Modern safety rated X and Y caps are designed for going across the AC line, and from the AC line to safety ground respectively and are designed to fail open if they fail. That blue cap is not X or Y rated, I'd bet. So a couple of bits of bad luck and the chassis can shock you. One more bit of bad luck and you could be electrocuted. It's happened before.

I am not a safety expert, don't pretend to be one. But I have seen and been advised (sometimes with a hammer ) on a few points of three wire grounding. I don't know if the following is sufficient to make the amp safe, but it's what was pounded into me:

If you're going to three-wire ground, do it so the chassis stays grounded. Crimp, don't just squash and solder, a ring terminal on the safety ground wire. Bolt the ring terminal to the chassis on a spot you've sanded free of paint and oxidation on a hole for a bolt holding the ring terminal to the chassis that is used for no other purpose. Use star washers above and below the ring terminal to bite into the metal chassis and ring terminal, and to keep the nut from coming loose. Also, unless you're using something like an IEC socket for incoming power and fuse, clamp the incoming line cord to the chassis so it cannot come loose, and would withstand a lot of pull - perhaps enough to lift the head of a head and cab amp. Use a grommet so the hole in the chassis doesn't cut into the line cord. And if you're not using an IEC socket, make the green wire to chassis longer than the white and black (or brown and blue in newer line cords) so the ground wire breaks last if the cord can be pulled loose.

I personally have completely disconnected the convenience outlets on my amps. I don't use the outlets, and they are all two wire on the amps I have, so even with a good safety ground in the amp, third wire ground doesn't go out the convenience outlet. I use the outlets as nice looking plugs for the hole in the chassis, nothing else.

Again: I am not a safety expert, just been pounded on by experts. There may be and probably are other issues that are needed to make your amp completely safe. And I do sometimes make mistakes, so you have to think through and research this on your own. And I view the internet as a poor place to learn things that my life depends on.

[EWaffle]

Thank you for all the useful information. I just want to do this myself because I'm a student and don't have money to be bringing this to a tech, but most of all I want to learn. There's no way to learn if I always have other people fixing my problems for me and I have no insight on the process. I always drain the amp and work with a hand in my pocket, I've never been shocked inside of an amp, only outside, and only by this amp. But I really appreciate your concern, thank you.

Now, seems the main thing you're saying is I need to get a secure connection from the green wire to the chassis. But right now, the green wire goes to a lug on the accessory socket (which nothing else is attached to) and then a wire goes from that to a lug on the tie strip (which nothing else is attached to, now that the death cap is out) and that lug is securely fastened to the chassis. Is that not enough?

[nevetslab]

R.G. correctly pointed out that the Green or Grn/Yel wire of the power cord needs to go directly to the chassis. In the current UL/CSA and harmonized European Safety Standards, a dedicated chassis screw is used for that grounding purpose and ONLY that purpose, with that screw fixed into the chassis, and the star washers on both sides of the crimped ring lug and a final nut to tighten it down. The chassis is prepared so it is untarnished bare metal, as that is the fault current path from the chassis, down the green wire to the AC mains building ground, and on to the planet where the mains panel is attached. This method is the lowest impedance path, whereas what you've inherited in the amp is not to that standard. And, of course, you need to verify that the AC mains plug at the end of your power cord...its' Ground pin DOES INDEED connect to the chassis. As others suggested, verify that by flexing the cable at the cable entrance to the chassis and at the plug, to be certain there aren't intermittent connections. It's all about proper electrical safety.

[g1]

How is that lug connected to chassis? A rivet? Or a star type washer between the chassis and the lug?
The paint should be stripped away and a star type lock washer used. A rivet is not acceptable.

Check resistance between the 3rd prong at the plug and chassis, you should have zero ohms.

The reason for all the concern is that if the chassis had been properly grounded via 3rd prong, you should not have been getting shocks.
You are focusing on the death cap, but that is only an issue when you have a 2 prong plug. With a properly grounded chassis, if you had a faulty death cap it should blow your circuit breaker.
Just trying to avoid you thinking you are safe because you removed the death cap, I don't think that is the case.

[Leo_Gnardo]

How is that lug connected to chassis? A rivet? Or a star type washer between the chassis and the lug?
The paint should be stripped away and a star type lock washer used. A rivet is not acceptable.

Agreed, my suggestion to use the tie strip was for convenience and it would probably work OK. But there's nothing like 100% assurance the grounding's done right the way you suggest, paint scraped away at the contact area and star washers used to dig into the chassis metal.

With a properly grounded chassis, if you had a faulty death cap it should blow your circuit breaker.

More than once in this series of Ampegs I've encountered faulty death caps, the white ceramic tube style. They never popped the breaker, but instead shot across the room trailing a shower of sparks and a coil of aluminized foil, spectacular! I learnt my lesson, now I just clip them out before stressing them with voltage.

[SoulFetish]

Thank you for all the useful information. I just want to do this myself because I'm a student and don't have money to be bringing this to a tech, but most of all I want to learn. There's no way to learn if I always have other people fixing my problems for me and I have no insight on the process. I always drain the amp and work with a hand in my pocket, I've never been shocked inside of an amp, only outside, and only by this amp. But I really appreciate your concern, thank you.

Now, seems the main thing you're saying is I need to get a secure connection from the green wire to the chassis. But right now, the green wire goes to a lug on the accessory socket (which nothing else is attached to) and then a wire goes from that to a lug on the tie strip (which nothing else is attached to, now that the death cap is out) and that lug is securely fastened to the chassis. Is that not enough?

If you live near Boston, MA, I'll wire the mains for you. These guys have already given you some really solid advice. Particularly when advising you to have a professional do this job for you. Or at the very least, do it with you and look it over. Make no mistake about it, this is THE most important electrical connection in your amplifier. Quite frankly, if you've already gotten strong shocks when touching someone else with the amp turned on, you are both lucky you've walked away from it. It takes hardly any current at all to do serious damage or cause a fatality.
from osha.gov/Publications/3075.html:
Below 1 milliampere Generally not perceptible
1 milliampere Faint tingle
5 milliamperes Slight shock felt; not painful but disturbing. Average individual can let go. Strong involuntary reactions can lead to other injuries.
6–25 milliamperes (women) Painful shock, loss of muscular control*
9–30 milliamperes (men) The freezing current or " let-go" range.* Individual cannot let go, but can be thrown away from the circuit if extensor muscles stimulated.
50–150 milliamperes Extreme pain, respiratory arrest, severe muscular contractions. Death is possible.
1,000–4,300 milliamperes Rhythmic pumping action of the heart ceases. Muscular contraction and nerve damage occur; death likely.
10,000 milliamperes Cardiac arrest, severe burns; death probable