Author Topic: Inside an EL84  (Read 498 times)

Offline El Sid

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Inside an EL84
« on: April 09, 2018, 08:31:18 PM »
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:


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.



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.



Offline Family_Dog

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Re: Inside an EL84
« Reply #1 on: April 09, 2018, 09:04:29 PM »
Heartbreaking when you see a dead valve! But note the care taken with construction, hundreds of thousands of these in their hey-days and retailing at 10/6 (R1.05) each for brands such as Mullard, Philips, Telefunken etc.

Why oh why did I not stock up on these at the time? Was initially taken in by the "wonders of solid state".


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Offline El Sid

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Re: Inside an EL84
« Reply #2 on: April 09, 2018, 09:12:05 PM »
The worst thing is that it was OK when i checked it last - the box must have been dropped.

Online Kent Kassler

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Re: Inside an EL84
« Reply #3 on: April 09, 2018, 09:50:20 PM »
This "humble" valve remains my favourite ever....don't ask me why but near every amp I have heard with them has been a winner to my ears....from st35 Dynaco to Leak Stereo 20 or old Fisher and the Scott Stereomaster 299a I picked up recently.....just wonderful....I'd take it over any of the larger el34/6L6/kt66/88 etc
« Last Edit: April 09, 2018, 09:53:14 PM by Kent Kassler »
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Offline Ampdog

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Re: Inside an EL84
« Reply #4 on: April 09, 2018, 10:34:17 PM »
El Sid.

Congratulations on excellent detail photography; being a 'sinner' myself, those are not the easiest of photographs to take well.  I have several other classic valves here on a stand, cut apart to show inner detail. In a way, one sometimes wonders how they are not more expensive!

Yes, about the best valve in the Pa = 14W class. Several manufacturers preferred to use them in push-pull-parallel topology, rather than more powerful single valves - Manley's Swordfish comes to mind. (The roughly equivalent beam valve, the 6BQ5 - with a lower - is also often used.)
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Online Kent Kassler

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Re: Inside an EL84
« Reply #5 on: April 10, 2018, 07:03:30 AM »
Would be interesting to examine a current production tube alongside....any glaring differences in material or construction that you might have picked up Ampdog?
« Last Edit: April 10, 2018, 07:06:18 AM by Kent Kassler »
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Offline marantz123

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Re: Inside an EL84
« Reply #6 on: April 10, 2018, 10:54:34 AM »
A sad demise of a true beauty there. Stunning in structure, and an amazing creation...so transparent, unassuming & honest...and unbiased.. :).. with nothing to hide.

Offline fredeb

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Re: Inside an EL84
« Reply #7 on: April 10, 2018, 12:42:24 PM »
Yes ! Thanks for the stunning photos El Sid . Very interesting .

Back to your amplifier ... I was wondering whether your mains transformer has any indication of current supported per tap .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
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Offline El Sid

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Re: Inside an EL84
« Reply #8 on: April 10, 2018, 02:39:38 PM »
Yes ! Thanks for the stunning photos El Sid . Very interesting .

Back to your amplifier ... I was wondering whether your mains transformer has any indication of current supported per tap .

I'll reply in the thread...

Offline Ampdog

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Re: Inside an EL84
« Reply #9 on: April 11, 2018, 04:06:06 PM »
......so transparent, unassuming & honest...and unbiased.. :).. with nothing to hide.

Very good description Marantz123!

Kent,

Yaaah .....  some makes rather hurriedly put together. Unneat underside (connections electrodes to pins); I occasionally had to wonder about a short.  (A G2 flat lead cut off at an angle, with sharp point no half-millimeter from say G1. But no internal sparking. The breakthrough voltage in vacuum quite substantial.)

Does 'neatness/consistency' matter if the valve tests well - I guess not.  But if I have to choose, It would be the neater valve. Consistency of construction: The most consistent in my experience:  The Tung-Sol 6L6GC/STR (special tube replica). Some 30 examples used here.

But please: I have not looked at/inside nearly all brands on the market!
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline El Sid

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Re: Inside an EL84
« Reply #10 on: April 11, 2018, 04:49:02 PM »
I have no idea which brand that valve is. None of the ones from that old amp I got have any markings left on them.

Offline fredeb

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Re: Inside an EL84
« Reply #11 on: April 12, 2018, 01:45:46 AM »
Does 'neatness/consistency' matter if the valve tests well - I guess not.  But if I have to choose, It would be the neater valve. Consistency of construction: The most consistent in my experience:  The Tung-Sol 6L6GC/STR (special tube replica). Some 30 examples used here.



They shore look purty too !
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts