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Old 24th April 2015, 09:08 AM   #1
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Cool The anatomy of a vacuum toob

So you have a little bit too much time on your hand, what do you do?
Dive into the spare parts pit and build another amp.
OK, done that. Now what?
What's this? These looks pretty useless, let's have fun, sorry, an educational experience (which is fun).

I came across some old 6550's from the time the Chinese knew how to make excellent firecrackers: the mid 90s.
Don't get me wrong, I'm not bashing Chinese valves: since the turn of the millenium some pretty decent types are being produced there.
These however are not.

They have been suffering in their lives.
As can be seen, there is very little getter left.
Time for an autopsy.
Meet mister hammer. What better way than to go out with a bang!
Click the image to open in full size.

OK, safety first. I don't want pieces of glass flying around my cave.
In a bubblewrap envelope they go.
Bam!
Bam!! Bamm!!!
Tougher glass (or better bubblewrap) than I thought.
Eventually -with a sharp pop- they gave up their vacuum.
Click the image to open in full size.

No need to cut the connection between the base and the anode structure, as bending it a bit was enough to snap most of them.
With weak welds like this, no wonder that there were reliability problems.
Click the image to open in full size.
Click the image to open in full size.

Next, remove the mica spacers.
Now this proved to be a harder task. All support rods have these crimped rings that fix them tight to the spacer.
Nothing that a pair of plyers and a decent amount of violance can't fix.
A view from the top.
Click the image to open in full size.

All elements separated.
Click the image to open in full size.

For the other one I decided to leave the electrodes in place and open up the anode instead.
Click the image to open in full size.
I wonder what happened to that cathode...

As can be seen, the pitch of g1 and g2 is the same.
Click the image to open in full size.

Thanks for watching and I invite you all to share more 'smashing' pictures.
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Old 24th April 2015, 12:47 PM   #2
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Great stuff!

The beam forming plate window is suprisingly wide.
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Old 24th April 2015, 04:10 PM   #3
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The grid wires are supposed to be aligned above (or behind) each other, those look like they are in between each other. Made perfectly wrong.

How long is that plate structure, 34mm?

Some 35LR6 and GU50 guts here:
GU-50 Dissected
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File Type: jpg rsz_35lr6_003.jpg (61.8 KB, 51 views)
File Type: jpg rsz_gu-50_0044.jpg (41.0 KB, 61 views)
File Type: jpg rsz_35lr6_001.jpg (51.7 KB, 57 views)

Last edited by smoking-amp; 24th April 2015 at 04:24 PM.
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Old 24th April 2015, 04:42 PM   #4
RJM1 is offline RJM1  United States
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Probably a noob question, but what are the three holes on each side of the plate for?
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Old 24th April 2015, 05:08 PM   #5
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The three holes in the plate are typically inspection ports for visually checking the grid 1 and grid 2 wire alignment on the production line. (the g3 frame has corresponding holes too)

You will find some plates with a little trap door that has been bent shut after inspection. And some later designs use tiny metal tabs on the grid frame ends that are crimped to the mica during alignment, these don't necessarily have the plate holes then, were assumed to stay aligned when the plate was slipped over. Also prevents mis-alignment when the tube gets dropped.

Last edited by smoking-amp; 24th April 2015 at 05:14 PM.
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Old 24th April 2015, 05:19 PM   #6
RJM1 is offline RJM1  United States
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Thank you.
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Old 24th April 2015, 05:27 PM   #7
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It looks like grids are not alligned, but that is the angle of the picture.
Looking straight at them, you can see only one. They are shadowing each other as they should.
You are close about the height, 35mm actually.
The box's width is 12,5mm (including wings 31mm) and depth 25mm. Magnetic.

Great pics from the GU50 and 35LR6
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Old 24th April 2015, 06:15 PM   #8
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"Looking straight at them, you can see only one. They are shadowing each other as they should."

Ahh, OK, that's good. I have a 36MC6 here from Ebay that DOES have the grids perfectly mis-aligned, and it behaves VERY badly. It looks OK on the curve tracer for a few minutes, but then the curves collapse down and the screen current goes ballistic. I guess it checked OK on a tube tester for a short duration test.

I may dissect that one someday, but I'm finding it interesting to observe on the curve tracer so far. But I do have a totally shot 36MC6 along with some other tube guts here:

from longest plate: 36MC6, 35LR6, 6HJ5, 21JV6/21HB5A, 12GE5
(36MC6 has the same size guts as 6LW6 or 6LF6)
(plate lengths: 36MC6 46 mm, 35LR6 41 mm, 6HJ5 35 mm, 21JV6/21HB5A 34 mm, 12GE5 28.5 mm )
Attached Images
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File Type: jpg Tube_plates_2.jpg (77.0 KB, 47 views)

Last edited by smoking-amp; 24th April 2015 at 06:44 PM.
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Old 24th April 2015, 06:55 PM   #9
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Quote:
Originally Posted by smoking-amp View Post
The three holes in the plate are typically inspection ports for visually checking the grid 1 and grid 2 wire alignment on the production line. (the g3 frame has corresponding holes too)

You will find some plates with a little trap door that has been bent shut after inspection. And some later designs use tiny metal tabs on the grid frame ends that are crimped to the mica during alignment, these don't necessarily have the plate holes then, were assumed to stay aligned when the plate was slipped over. Also prevents mis-alignment when the tube gets dropped.
Those 'inspection holes' are confusing.
Not all types have them, some had them introduced later in life, some have them but the grid wires not visible.

The original GEC KT88 had solid plates, as did the Tesla version. All modern clones have holes (except for a recent Chinese version).
I quickly grabbed some US 6L6 variants and: no holes.
Early Chinese and Russian 6L6s no holes, recent ones with.
The 6550 started at Tung Sol without holes, later Tung Sols and GE's had holes.
The GEC KT66 has very large windows, but the beam plate blocks the view of the grids. Was the beam plate inserted after the anode was fixed to the mica spacers?
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Old 24th April 2015, 07:08 PM   #10
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Yeah, I don't know what the story is with those beam plates with the holes in the wrong place. Could be beam plates from another tube were in stock and the right ones weren't?? I don't know. Annoying, because I like to visually check (with a magnifying glass) the grid alignment. Some tubes are not so perfectly aligned there. The little metal tab aligners, at the ends of the grid frames, (crimped to the mica) may have later obsolesced the visual alignment holes.
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