valve testing el84 only

[Phil Y]

Hello Phil,

It looks like you want to DIY but have you seen this ?
http://www.hotroxuk.com/orange-vt1000-valve-tester.html
Not very cheap but interesting I thought.

Phil.

[Richard]

Search Mullard el84 PDF online for the data sheet. An amp schematic might show NC if there isn't a connection used in that application but the data sheet shows IC with g3 connected to k in the Mullard for example and other pins beware as John says.

[Richard]

Interesting unit Phil. Dedicated socket for el84 but no triode power valves and limited small valves.

[Phil Y]

Hello Richard,

Yes, a bit limited but as it is made by Orange it is no doubt aimed at guitar amp users. Maybe they will develop a more versatile unit in the future. Buying an old AVO or whatever is an expensive and potentially risky option.

Phil.

[oceanobsession]

Originally Posted by John Caswell

Oceanobsession,
Contrary to what you say "el84 pins 1 6 8 are not used".
This is incorrect, they are internal connections and can be used for anything depending in the whim of the manufacturers.
I have had several makes on the bench at the same time and all have differing internal connections to them, mainly to support the structure.
Proceed with care!!

John

Yes I take your point, but for my project I would not connect to these pins
that is what im saying , and yes I shall proceed with care . me phil.

[Richard]

Hi Phil, yes nice if you use those valves. A bigger range would doubtless cost more. I've been trying to think of an easy way for Phil as it looks a lot of work just to test el84.
Does the Manley have cathode resistors as well as adjustable grid bias? If so he could set the neg grid bias correct on one socket with a known good valve, leave it on that setting, then insert valves in turn into that socket and check their currents by the voltage across the cathode resistor.

[Richard]

Found the manual. Each el84 has a 10R cathode resistor and meter probe points. Says set to 250mV.
So set one with a good known valve then check the others in that same position for a comparison.

[Richard]

Doing that will set the control valve to 25mA (0.25/10). You wouldn't know the grid bias but could see how closely other valves were to the control in their current draw.

[oceanobsession]

Originally Posted by Richard

Doing that will set the control valve to 25mA (0.25/10). You wouldn't know the grid bias but could see how closely other valves were to the control in their current draw.

Hi Richard , thanks for your help , I did think about this what you are suggesting and have 8 new jj el84 matched set , if I fit say one new valve into
no 1 position and set the bias adjustment to 250mv then remove that valve
and fit a secondhand ei el84 and take a note of the difference , would a low
reading say 100mv mean that the valve was worn and a high reading say 350mv mean that this valve was better than new , I have been on the look out
for a taylor 45c valve tester , but until then . cheers Richard

I also considered building this one http://www.valveheaven.com/2015/03/a...vetube-tester/

[Richard]

Phil, yes pretty much exactly that. Valves for p-p are usually matched to 10% on current. Ideally you'd check slope as well but a set of new which match on current are almost always close on slope ime.
I'd set the socket with one of your new ones then check and mark each of the rest in mA (the V reading divided by 10) on them with a CD pen. Then you can pair them up and check the old ones too.
Old ones tend to draw less as you say. If you find a high one it may just have got in there by poor matching but it may be on the way out so pair it carefully and watch it.
Also don't be surprised if the old and new sets are different as new new valves may differ quite a lot before matching. (I did 20 6550 a while back and they varied 40-70mA.)
They would then be relatively matched rather than to any absolute value but if the control valve is known good that will be fine.