Deathcap X2

[Lonely Raven]

So I'm cleaning up some of the hack wiring that someone did to the Alamo amp I just picked up. Looks like someone touched up some solder points with some thick sorta cheap assed solder...probably not even electrical solder.

Anywho, this thing has a cap going from the black line on the power switch to ground, but also has a cap going from the white line to ground.

I'm figuring it's a good idea to remove both of these "death caps", yes?

[Structo]

Depending on the values they might have been an attempt to shunt RFI to ground.

[Lonely Raven]

Depending on the values they might have been an attempt to shunt RFI to ground.

Sangamo USA
.02 600

Both of them the same.

I was confused because the one going off the white power lead was coming off pin 5 of the Recto tube...but then I realized they just used an empty pin as a jumper point.

I have the one on the black lead removed, I figure I'll pull the one on the white lead unless I'm ruining something. I just want to clean the amp up while I blueprint it, and maybe make a clone for my dad. I'm already drawing up a cabinet that I'll make out of some neat wood, maybe even cut it all out on the laser.

[CaseyJones]

Gee Dad, why do they call it a "death cap"?

I was working on yet another shitbox old amp Wednesday. It had a hum problem so just for giggles I figured I'd improvise a three prong cord by strapping the chassis ground to my ground fault protected outlet with a jumper, this in additon to the original non polarized two conductor cord. Of course the outlet tripped instantly. I'm not as bright as I pretend to be so I reset the outlet and tried again, same result. O.k., I'm not entirely stupid so I checked the chassis back to the outlet ground and found 121 volts on the chassis! I lifted the death cap out of the circuit and checked it, it was shorted.

[Johnhenry]

it's there for a reason, and it should only be on the grounded side of the AC supply line,
It put's the Chassis at Ground Potential for AC Frequencies,
Without this cap you will probably get a small amount of Voltage Leakage from your power transformer that will cause the voltage to float up and down and put some hum in your amp,
This cap simply shunt's the Chassis voltage to ground reducing the amount of voltage and hum,
Old amp's and old transformer's may exhibit more hum than newer one's
I alway's replaced with a new 600 V cap on old amps i serviced.
Johnhenry

[Lonely Raven]

Gee Dad, why do they call it a "death cap"?

I was working on yet another shitbox old amp Wednesday. It had a hum problem so just for giggles I figured I'd improvise a three prong cord by strapping the chassis ground to my ground fault protected outlet with a jumper, this in additon to the original non polarized two conductor cord. Of course the outlet tripped instantly. I'm not as bright as I pretend to be so I reset the outlet and tried again, same result. O.k., I'm not entirely stupid so I checked the chassis back to the outlet ground and found 121 volts on the chassis! I lifted the death cap out of the circuit and checked it, it was shorted.

Well that's one vote for removal.

[Lonely Raven]

it's there for a reason, and it should only be on the grounded side of the AC supply line,
It put's the Chassis at Ground Potential for AC Frequencies,
Without this cap you will probably get a small amount of Voltage Leakage from your power transformer that will cause the voltage to float up and down and put some hum in your amp,
This cap simply shunt's the Chassis voltage to ground reducing the amount of voltage and hum,
Old amp's and old transformer's may exhibit more hum than newer one's
I alway's replaced with a new 600 V cap on old amps i serviced.
Johnhenry

Why would this amp come with one on each side of the power cord then?

[Johnhenry]

You got me on that one, you may get away without the cap, but due to the age of the amp i would bet there's gonna be some voltage bleeding and hum without it, I've had this problem with old and rusty transformer's .
John

[Phil_S]

it's there for a reason, and it should only be on the grounded side of the AC supply line,
It put's the Chassis at Ground Potential for AC Frequencies,
Without this cap you will probably get a small amount of Voltage Leakage from your power transformer that will cause the voltage to float up and down and put some hum in your amp,
This cap simply shunt's the Chassis voltage to ground reducing the amount of voltage and hum,
Old amp's and old transformer's may exhibit more hum than newer one's
I alway's replaced with a new 600 V cap on old amps i serviced.
Johnhenry

I don't think this addresses the question. In the bad old days, when non-polarized two prong plugs were used, there was some bad thinking that the death cap actually did something for the consumer, and maybe it did, so long as the cap didn't short. How do you think it got this moniker?

Remove them and put a proper 3-prong power supply plug on the amp.

I've built several amps and have no such experience with any power transformer induced hum, at least nothing that one would notice. Frankly, I don't see the point of putting a cap on the ground side of the AC supply and this is the first I've seen a recommendation to do this. I must be missing something here.

[CaseyJones]

My cost for a 16/3 power cord with a molded plug is $3.00. The only reason I'll screw around with a two conductor cord is if the customer insists on total originality in a vintage amp, OR to baseline the amp before I seriously get into it. By "baseline" I mean take inventory of what it is and what it does before I get into it.

It's pretty easy to sell a vintage nut on a three conductor cord if I can light a light bulb between the chassis and a bonafide ground.

[Structo]

it's there for a reason, and it should only be on the grounded side of the AC supply line,
It put's the Chassis at Ground Potential for AC Frequencies,
Without this cap you will probably get a small amount of Voltage Leakage from your power transformer that will cause the voltage to float up and down and put some hum in your amp,
This cap simply shunt's the Chassis voltage to ground reducing the amount of voltage and hum,
Old amp's and old transformer's may exhibit more hum than newer one's
I alway's replaced with a new 600 V cap on old amps i serviced.
Johnhenry

Why would this amp come with one on each side of the power cord then?

The reaspn there was two caps is because the plug was not polarized, right?
So it would have a shunt to ground no matter which way the plug was?

.02 uf is a bit big for RFI filtering, yes?

So it was just like Raven said, deathcap x2?

How about on those old amps that run on straight house current with no power transformer?
Is the best way to deal with those a 1:1 isolation transformer to remove the physical connection to the chassis?

[Lonely Raven]

Plug is non polarized, and there is no polarity switch. Just ON/OFF, Tone and Volume.

[Johnhenry]

I don't know why it's called a Deathcap ? in the 40 year's i worked on amp's i never heard of a single person here in the US getting electrocuted while playing a guitar on stage. i've seen plenty Newb's get the crap knocked out of thierself's by useing to much hand inside the amp, Seen plenty of people get shocked due to ground loop's,
But tell me, How many guy's you know that died due to this cap being in thier amp ?
Johnhenry

[CaseyJones]

I don't know why it's called a Deathcap ? in the 40 year's i worked on amp's i never heard of a single person here in the US getting electrocuted while playing a guitar on stage. i've seen plenty Newb's get the crap knocked out of thierself's by useing to much hand inside the amp, Seen plenty of people get shocked due to ground loop's,
But tell me, How many guy's you know that died due to this cap being in thier amp ?
Johnhenry

You're kiddin, right? 40 years and you've never had a ground loop kick yer ass?

Someone out there took inventory of all the guys they could think of who were knocked for a loop by electronic faults primarily a hot chassis or a hot chassis in relation to other gear. It might not kill you but there's nothing quite like trying to remember the next chord after getting' zapped or tryin' to remember the lyrics after steppin' up to the mic and gettin' a whack to the lip.

[Structo]

I can't remember the name of the group in the 70's where the singer was electrocuted on stage by having a hot chassis then touched his lips to a grounded mic.

Ah, found it, Stone the Crows.

The tragic death of Les Harvey (electrocuted by a live microphone on stage at Swansea's Top Rank Suite in May 1972) almost led to the breakup of the band. After trying Peter Green, the band brought in ex-Thunderclap Newman prodigy Jimmy McCulloch as lead guitarist.

http://en.wikipedia.org/wiki/Stone_the_Crows