Inside an EL84

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El Sid

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In a box of goodies on my shelf I found an EL84 that had been cracked. So obviously I had to dismantle it and have a look inside. For the benefit of those who may be interested, here are some photos:

Cracked open, with half of the anode/plate taken off to show the insides:
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Both halves of the anode removed for a clearer view. I'm sure most of you know this, but I'll describe the bits and pices for those who don't. The innermost white part is the cathode, a flat, oval tube with the heater inside, coated in an oxide mixture which encourages thermionic emission of electrons. The two brass-coloured supports on either side are for the control grid - it is a spiral of wire wound around them. its proximity to the cathode is what allows a small signal to control the current through the valve. The next set of supports are for the screen grid, and the outermost for the supressor grid.
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A close-up to have a better look at the grids. The control grid is the tightest spiral, with the screen grid having a spacing around four times greater. The supressor is much futher out.
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