DO-35 diode inside vacuum tube ? - diyAudio
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Old 8th February 2009, 04:37 AM   #1
pjp is offline pjp  India
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Default DO-35 diode inside vacuum tube ?

Well not really!

But what is this thing that looks like a DO-35 diode inside the glass
envelope of a vacuum tube: http://www.r-type.org/pics/aaa0772b.jpg

(Like to page: http://www.r-type.org/exhib/aaa0772.htm )
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Old 8th February 2009, 05:01 AM   #2
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^^

Looks like a fuse.
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Old 8th February 2009, 05:18 AM   #3
pjp is offline pjp  India
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The 'fuse' is not accessible. If it blows you'll have to throw out the tube.

Is there some seriously catastrophic scenario that needs such extreme protection ?
(I'm a tube noob)
(if it is a fuse, its protecting the gate)
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Old 8th February 2009, 05:18 AM   #4
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Quote:
Looks like a fuse
How is the fuse changed when it decides to blow
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Old 8th February 2009, 05:23 AM   #5
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Its' a small signal RF diode............the kind we all used making our first AM radios!!
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Old 8th February 2009, 03:55 PM   #6
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Looking at the close up view in the last picture on the page here
http://www.r-type.org/exhib/aaa0772.htm

it appears to me to be some sort of mechanical support or stiffener. The lead going through it does not seem to actually go anywhere, it seems to be curved like a spring and is pressing against the bottom structure. Perhaps it reduced microphonics ??

If it was electrically connected somehow that I cant see then perhaps it is some sort of spark gap protection ??
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Old 8th February 2009, 08:47 PM   #7
pjp is offline pjp  India
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It isn't a support.
Its the only connection to the grid (gate).
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Old 8th February 2009, 09:55 PM   #8
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Quote:
Originally posted by pjp
It isn't a support.
Its the only connection to the grid (gate).

It appears to me that it goes to pin 5 which is open, and the thin line through it appears to be nothing more than a distorted image of a lead behind it. To me it appears to be nothing more than a support. (I'm using a very good CRT monitor and image magnification and that is what it looks like to me.)

Tubes have grids, fets of various descriptions have gates.
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Old 9th February 2009, 02:20 AM   #9
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Quote:
Originally posted by kevinkr
It appears to me that it goes to pin 5 which is open

Now its beginning to make sense to me - perhaps the purpose is to provide mechanical support without the inductance of a lead (at VHF) ?


Is such a mechanism employed in any other tube ?
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Old 9th February 2009, 03:33 AM   #10
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Quote:
Originally posted by pjp

................ mechanical support without the inductance of a lead (at VHF) ?
I don't think so . The purpose is to provide INSULATION , between the internal electrode where it is connected and the
external pin 5 .

kevinkr is correct !!

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