Portrait of a tube
EL34 TESLA
Author Jac van de Walle
sorry for the bad picture quality, but this is only a Canon camera that cost me 500 Euro. Next one will be another brand. This is a NOS Tesla EL34 from teh 1960's , that had a glass crack after burn in. This confirms what I always say, micro cracks can survive for decades, and get activated after first use. Well, luckily this is rare. Actually the crack developed beginning from the base, which is what they useually do.
It begins when I removed the glass from the tube, the mica is nicely tight to the glass. So no rattlle. Not that rattle matters, and this is not microphonic, but people just don't like it.
Unlike the Chinese Shuguang "so called" quality product by a group of English collectors... (read here), the Tesla tube was mounted on hard nickel wires, and the Chinese tube was mounted on cheaper copper wires. So I mean the wires that feed trough the glass (the "pearls"). Price difference of that, I would say it's 0,2 cents per wire, but fair enough at 8 wires it costs 1.6 cents more, and this is the reason the Chinese use copper. The disadvantage is the tube gets damaged easy in the mail, or when you drop it yourself.
Well seriously, it rather works like this: When the Chinese factory builds 400.000 pcs EL34 per year, we talk about an extra costs of 6400 Euro, just for EL34. And then they build 6L6, and KT88, and KT66, and... and... So the saving all together is large, and it pays for the salery of the director nicely. This is how Chinese work. Save on the glass, and on other things. I do not try to make the Chinese look bad, but thsi was an obvious saving with the Shuguang, that the Tesla did NOT have.
Double Halo
Taiwanese Plyer versus Czech EL34.
This is what happens when you cut hard nickel.
Some interesting details of the tube base
| This is how the heater wire came out. Note the "bend" in one end. This was not me. The wire is very hard, and is like a spring. This seems to me how they fixed the wire inside the cathode sleeve. |
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Cathode sleeve, the scratch in the middle is by me.
Cathode detail.
There is some spiral shaped scratching on it. For the rest, note the beautiful uniformity. Also there is no burn of any kind, so yes this was a NOS tube indeed. If the tube is used, ther comes a greyish pattern on the cathode, like a shade from the first grid.
First Grid
The first grid of EL34 must be gold plated. If you look at the bottem of the grid, you can see the yellowish color.
Second Grid
The second grid can become very hot, so it is carbon plated, as black color radiated heat better.
Third Grid
This is what makes an EL34, an EL34 and not a 6L6. It is a real three grid tube.
Mica
THE END