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Old 31st January 2003, 11:15 AM   #31
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Quote:
Originally posted by Joel


Exactly. I think "Doc Bottlehead" (WTF???) is taking a big risk in hoping that all the units you hook this thing up to will have a resistance to ground.

DocB has sold a few thousand of those amp kits, with a very good reputation for reliability. He, along with Paul Joppa and the late John "Buddah" Cammille, have brought some very good products to market. It was DocB and cohorts that reintroduced "Parafeed" output topology and the C4S to the masses - both of which have become well-respected and copied.

The "Barnum" statement posted elsewhere in this thread is just another example of the great unwashed and anonymous opining on the Internet. Take your designs, make them affordable, have people buy them and become faithful customers, then you can make such statements without sounding like an ***.
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Old 31st January 2003, 11:26 AM   #32
dhaen is offline dhaen  Europe
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Default What's the argument?

With no apparent DC path, the grid will most likely drift in one direction or the other, it depends on the valve.
The actual likelyhood is that a DC path does exist through the coupling component or cable leakage.

Cheers,
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Old 31st January 2003, 02:33 PM   #33
Joel is offline Joel  United States
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Quote:
Originally posted by Gabevee
But note the non connected one. Grid not connected to anything... tube works. Tube theory from the one who invented the thing!
Gabe, c'mon. A tube merely showing plate circuit current does not qualify as it "working".
A triode amplifies.
Let's consider the picture below. Where is the discharge path for the capacitor?
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File Type: jpg nogrid.jpg (5.1 KB, 135 views)
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Old 31st January 2003, 02:37 PM   #34
SY is offline SY  United States
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Quote:
The "Barnum" statement posted elsewhere in this thread is just another example of the great unwashed and anonymous opining on the Internet.
You're welcome to question my hygiene, but "anonymous" is a lie. A minute spent at my profile and chasing a link of two will demonstrate that I've not done much to hide my identity. What did you think of the mermaid?

(edit: I see that the profile button doesn't exist in the new BB software, but the link to my homepage still does)
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Old 31st January 2003, 02:39 PM   #35
dhaen is offline dhaen  Europe
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Joel,

Quote:
Where is the discharge path for the capacitor?
If I may comment....
The discharge route is through the leakage of the capacitor.
Which is an unreliable factor.

Cheers,
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Old 31st January 2003, 02:41 PM   #36
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Default MY GOODNESS

Hi,

Is this really worth any more energy?

Leaving the grid to the elements is just not good engineering.Period.

Cheers,
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Old 31st January 2003, 03:17 PM   #37
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Joel,

As dhaen says the discharge is through the capacitor. When the other side of the cap goes to the opposite polarity, the cap discharges.

Fdegrove,

You are absolutely correct sir. The practice is not good. But the theory is still correct. BTW, 100K grid resistor? Kinda low, IMHO. It does tend to source grid current.

Sy,

While I agree with you, the amplifier that Bottlehead puts out uses a fixed bias (solid state, for that matter) at both the plate and cathode of both the driver tube and the output tube, with DC NFB, so DC bias remains stable. A floating grid will work fine, IMHO.

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Old 31st January 2003, 03:22 PM   #38
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Default GRIDLEAKS

Hi,

Quote:
BTW, 100K grid resistor? Kinda low, IMHO. It does tend to source grid current.
Although it was just an example...the value will depend on the tube used,won't it?

Cheers,
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Old 31st January 2003, 03:28 PM   #39
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fdegrove,

I suppose. I think it depends on transconductance.

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Old 31st January 2003, 03:47 PM   #40
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Quote:
Originally posted by Joel


In fact, that's exactly what it does.

Here is some reading online:
http://www.tpub.com/neets/book6/20f.htm

And this describes diodes when presented with an AC voltage:
http://www.tpub.com/neets/book6/20b.htm


cheers
Hummm none of those links say the diode stops being a diode when it's not forward-biased....

In fact, the first one even says that a triode's grid will act as a diode plate when positive.

So, is the G-K diode real?

Perhaps I should ask you, is a car a car only when it's running? When it's off, is it no longer a car?

Ok back to the topic. I never said it'd be stable nor useful (except in high-impedance circuits, such as an electrostatic sensor), but it will work with no apparent DC grid bias.

Tim
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