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Old 9th May 2006, 08:06 PM   #1
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Default grounding case of 6j5

Does anyone have any suggestions on whether it is necessary (for safety reasons) to ground the case (which is metal) of a 6j5, and, if so, how to do it?

-d
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Old 10th May 2006, 12:29 AM   #2
EC8010 is offline EC8010  United Kingdom
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Not necessary, but it may reduce hum and it will (very slightly) reduce Cag. Pin 1 to chassis.
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Old 10th May 2006, 01:13 AM   #3
SY is offline SY  United States
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How to do it involves a special socket with a skirt around the tube base and springy fingers inside. You can improvise one with tin shears and some spring steel shim stock.
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Old 10th May 2006, 04:32 AM   #4
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Default Re: grounding case of 6j5

Quote:
Originally posted by dsavitsk
Does anyone have any suggestions on whether it is necessary (for safety reasons) to ground the case (which is metal) of a 6j5, and, if so, how to do it?

-d
It'll work much better. As for how, make certain that the metal envelope is the most negative part of that tube. This will usually be the case if it's connected conventionally: plate to positive DC rail + cathode bias. Even if using fixed bias, it will still be at the same potential as the cathode, and that's good enough. If the case isn't more negative than the cathode, it will behave as another anode, and that'll likely lead to problems.

Sy: WTH're you talking about? With those metal Octals, pin #1 is connected to the metal case.
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Old 10th May 2006, 11:32 AM   #5
SY is offline SY  United States
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Miles, sorry, I've not used a 6J5. I should have looked at the data sheet. Most of the tubes with external shield that I've used were RF types or Nuvisters that required external connection to case.
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Old 10th May 2006, 12:09 PM   #6
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Default Re: Re: grounding case of 6j5

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Originally posted by Miles Prower
If the case isn't more negative than the cathode, it will behave as another anode, and that'll likely lead to problems.
That's a very good point. Scrub my recommendation of tying the can to the chassis; tie it to an AC ground with a lower DC potential than the cathode. Often, that will be the chassis, but not always.
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Old 10th May 2006, 12:40 PM   #7
Joel is offline Joel  United States
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Default Not quite right

Quote:
If the case isn't more negative than the cathode, it will behave as another anode, and that'll likely lead to problems.
If the metal envelope is at the same potential as the cathode, it cannot act like another plate. In all situations, you can connect pin 1 to the cathode. From my experience, this is preferred - I've used the 6C5, 6J5, 6J7, 6SJ7, 6F5, and 6Q7 in many projects. When Rk is bypassed, it's ok to ground it.

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Old 10th May 2006, 04:10 PM   #8
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Default Re: Not quite right

Thanks for the suggestions.

Quote:
Originally posted by SY
I should have looked at the data sheet.
I should have too as i now notice pin 1 connected to the case.

Quote:
Originally posted by Joel
If the metal envelope is at the same potential as the cathode, it cannot act like another plate. In all situations, you can connect pin 1 to the cathode. From my experience, this is preferred - I've used the 6C5, 6J5, 6J7, 6SJ7, 6F5, and 6Q7 in many projects. When Rk is bypassed, it's ok to ground it.
I was going to use these in an ultrapath design, so I'll try pin 1 to ground and to the cathode to see if there is a difference.
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