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RE: Moths??.

Posted by tube wrangler (M) on August 25, 2009 at 20:55:13

In Reply to: RE: Moths??. posted by Paul Joppa on August 25, 2009 at 11:25:19:

Paul, all of this makes good sense and parallels my experience with them.

I have some theories on this (beware!) that may or may not make any sense-- bear with me.

When they are new-- if really new-- they are going to really conduct-- be careful!

If they've been stored, I suspect that they should be very carefully "ramped-up" a few times before you trust them in a full-voltaged situation, even though conduction-- initially-- is less, as they are unstable until used a bit..

I think that they can take much less plate current than non-mesh types--the woven mesh just doesn't like anything (in the 2A3) over about 46ma.

I think they like the 2A3 standard of 250 volts from Plate to Cathode OK.

There are Woven mesh-plates, perforated so-called mesh-plates, and solid plates.

I have some old AVVT 2A3 solid plates. They are identical to the woven mesh except for the plate.

These have far more power, punch and Bottom-End than the Meshies I normally use. Their Highs are more pronounced also, but the many natural layers that are present in music are fewer, and it is harder to separate individual musical lines and events taking place during a performance-- where a lot else is also happening on the recording.

The Perf.-Plates (Chinese manufacture-- only the best ones) that I have tried have better musical layering and depth of images than any solid-plate I have used, but can't begin to compare to the AVVT or EML woven mesh.

Here's where I hit the ?? (questionable) department:

I suspect that there are collisions between the insides of Solid-Plate tubes and the other elements in the tube-- that is, electrons hit the solid plate, and bounce. The advantage of the solid-plate (if it is a symmetrical tube) is that all target distances (other-elements-to-plate) should be the same. I have used Eimac and other symmetrical Solid-Plate tubes and found the same characteristic to a lesser degree-- that is, their ROUND plate structure seems to exhibit less electron-bouncing troubles than a wide, flat plate, but they still can't compare to a woven mesh for ultimate musical-capture quality..

I suspect that the Perf-Plates have less bounced electrons simply because there are holes for some of them to hit, or miss, and some electrons may just go through, and I suspect that SOME collisions (hitting the sides of the holes, etc.), are at a higher frequency than the collisions of electrons hitting a solid plate.

I suspect that gives you a "smorgasbord" of different kinds of collisions and different sonic artifacts, which are added-in to the main signal, and make music sound euphonic, but to me, it is also distorted in many ways which are audible on very High-Eff. speakers.

This leads me to understand why VAIC and KRON labored so mightily to produce a (expensive, and a real headache to make) WOVEN mesh-plate.

This design necessitated use of a "Waterfall" type filament frame-structure to match the overall frame-grid style of tube architecture.

Since there are 8 vertical filaments welded in parallel, instead of a long, folded one, with huge bias differences from one end to the other-- the welded Waterfall filaments (all 8) would provide a clean, linear filament structure.

I suspect that the woven mesh never bounces much electron energy back-- it just "catches" it-- into the mesh weave.... it gets caught in there.

This design has one slight disadvantage, and that is the fact that different parts of the weave have high spots, average depth spots, and low spots.

The differences in these different path lengths also add-in a euphonic depth for the same reason that some other tubes do-- there are different path lengths, and the sonics from each length are added together, giving a sonically "fuller" signal.

Still, these path lengths do not differ by very much, so the tube is able to sound reasonably clean, very honest and coherent anyhow.

You lose some High-end extension, and quite a bit of Bottom-End energy and power-- as compared to Perf-plates, and even more as compared to soild-plates-- all else being equal.

But I consider the EML and AVVT woven meshies overall, when playing music, as the state-of-the-audio art in tubes-- especially the 2A3 and the 45-- which are built very similarly and sound virtually alike in all regards.

This is not true with other 45 types and 2A3 types-- with NOS, for instance, there is a LARGE difference.

But, with the latest EML's, the only audible difference between their 45 and their 2A3 is the operating current that the circuit sees, and the grid admittance characteristics that are related to plate current.

EML makes both of these tubes so well, that I would pay twice as much for them if I had to.

For what it's worth, an amp using true-mesh output tubes will not measure as well as the same amp running solid-plate tubes.

---Dennis---

Edits: 08/25/09

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