How to find out which is which????

[jamesjung21]

Hi guys,

I have a 'dump' of tubes, which contains tubes labelled EL8 and their last # rubbed off... They are either EL86 or EL84

And I want to separate EL84 from EL86, but I currently have no tester nor a circuit to find it out...

Does anyone know how to distinguish the two different types just by using a DMM (multimeter) and differences in their internal/external appearances?

I found that some of them have their 8th pins connected to the plates, while some others don't...

I previously managed to separate ECC88 from PCC88 by using the difference in the heater resistance....

Thanks,
JayJay

P.S: Have Telefunken ever manufactured EL84 with non-round plates? If round, it should look like () when viewed from the top, whereas the non-round plates in pentodes would look like [].

[PRR]

> I want to separate EL84 from EL86

http://www.r-type.org/exhib/aad0122.htm
http://www.r-type.org/exhib/aaa0028.htm

You can't tell the difference by eye or meter. Up to 200V and 48mA, they are the same tube (not counting different details used in different years or factories). And over 200V or 48mA, both will work fine for days.

The EL84 can also be run to 250V, the EL86 can also be run to 64mA. In theory, if you worked the tube over 200V 48mA, you'd want to know the difference. But the only difference will be life. If you put 250V on an '86, you are 25% over the rating and life will be shorter. Likewise a 64mA application wants an '84. But probably thousands of hours either way. And I kinda suspect that both tubes ARE the same, and the two type numbers are about marketing rather than rational design.

If you got them cheap, go ahead and use them as whichever.

> I found that some of them have their 8th pins connected to the plates, while some others don't...

Pin 8, on either type, is "IC", internal connection. They don't say WHAT it is connected to, and the fine print says you should NOT use that socket-lug as a tie-point, implying it could be connected to anything or nothing. Seems like some of your tubes use this pin to brace-up the Plate, and others don't.

[fdegrove]

Hi,

Most, if not all, European made tubes carry an acid etched code used by the manufacturers.

If you have a key the decipher that you will know exactly what type of tube it is.
The difficulty lies in finding the correct keys as alot of tubes where not made "in house" especially around the late Sixities, early Seventies era.
I think I have keys for most Philips tubes and their subsidiaries such as Mullard, Valvo, etc.

Should you care to jot down these codes and post them here I'll try to decipher them for you so you'll at least jnow which is which.

Cheers,