Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: thud33 on July 09, 2023, 06:48:00 am
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I kicked this around in a Facebook group that I belong to, but I’d be grateful for input from the sages here. I am working on a 1973 Earth Sound Research G-2000 head (essentially a Twin Reverb clone) that still has its original .01uF “death cap” and unpolarized two prong cord. I’ll replace the cord with a chassis-grounded 3-prong, and I’m strongly inclined to remove the cap. Some people in the other group suggest to keep the cap, saying that with the new cable, the fuse will blow if the cap ever fails to short. Just seems like a bad idea to me. I get that the cap has an RFI eliminating function, but I guess I’m not too worried about excessive noise. I’m also not worried about ground loops given that the amp will be used stand-alone. What about replacing the cap with a Y-rated safety cap? Thanks for your advice!
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If a person wants to keep a functioning ground switch then these would work https://www.justradios.com/X1Y2capacitors.html (https://www.justradios.com/X1Y2capacitors.html)
Rob Robinette has some information on this subject https://robrobinette.com/Death_Cap_and_Ground_Switch.htm
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I like RR's take on this. As with most things, he is pretty thorough.
I cannot think of a good reason to keep a functioning ground switch - am I missing something?
I remove the cap, although since I play at home these days, I do not think it necessary. I have never experience increased noise after removing the cap - if I did I would use a Y cap. The last band I played in practiced in an old house. I brought a portable GFCI with me. I'm surprised more folks don't do this.
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mresistor, bmccowan, thank you for your comments. If this were a hi-fi amp, I’d think that a polarized two prong and Y1/Y2 cap might be the way to go. Unless someone makes a good argument for doing otherwise, I’m removing the death cap and ground switch. I will also disconnect the courtesy outlet, maybe leave it in for cosmetics?
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I leave the convenience outlet - just disconnect it. Ground switch can be repurposed, like maybe disconnecting or changing NFB. Or you can leave it in place, disconnected and tell people its the British switch and watch as they try to discern the difference.
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If you want to keep the death cap on the circuit you can, but you must swap it with an Y2 class cap
Y2 caps are planned for that purpose, no other cap there
If they burn, they burn open and didn't short
Franco
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I have a feeling nobody read through this https://www.justradios.com/safetytips.html
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I can't remember ever having read that web page but all that info has been common knowledge in my line of work since way before there ever was a webpage. :icon_biggrin:
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I did. And I think its accurate/helpful. But for a variety of reasons I think the situation is different for radios and HiFi. For one thing, you do not have a guitar plugged into your radio or HiFi - or at least you shouldn't. And ground loops between components can be more troublesome in HiFi equipment. So all my guitar amps have a 3 wire power cord properly installed. No line cap and no ground switch. I have rebuilt several classic tube HiFi amps. They have 2-wire cords and some rainy day I will install Y caps in them.
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....still has its original .01uF “death cap” ....
Point Oh One??
That's not even a "painful sting" cap.
It is about 270K at 60Hz. Or at 120V it is 0.5mA. It won't even trip a GFI.
Are you sure you read that right?
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PRR, yes, on both the component and the schematic. I thought it was low, too. Aren’t they often in the 0.047 range?
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I can't remember ever having read that web page but all that info has been common knowledge in my line of work since way before there ever was a webpage. :icon_biggrin:
Al Gore hadn't invented it yet. :laugh:
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That's not even a "painful sting" cap. It is about 270K at 60Hz. Or at 120V it is 0.5mA. It won't even trip a GFI.
Somehow I had the understanding that the cap itself was not the problem, but that when it failed the chassis (and guitar) would be energized to line voltage. Is that not correct?
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That's not even a "painful sting" cap. It is about 270K at 60Hz. Or at 120V it is 0.5mA. It won't even trip a GFI.
Somehow I had the understanding that the cap itself was not the problem, but that when it failed the chassis (and guitar) would be energized to line voltage. Is that not correct?
That's correct. But, even when the cap is working properly if the power cord is flipped such that the 120V hot wire is connected to the cap, the cap will pass enough current to really sting your lips when you kiss the mic. This depends on how the PA power cord is plugged in. Best to slap the mic before you say "Testing, 1, 2, 3". :l2:
But the moment you properly installed that three prong power cord, the death cap ceased to exist. Unless the house wiring is faulty.
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Thanks for the correction, acheld.
..... Unless the house wiring is faulty.
And that never happens!
(Not more than 60% of the outlets in my last house's kitchen.)