Testing EL34's

[Lake Placid Blues]

I recently tested a bunch of El34's from my singles collection that I have built up over the years and thought some may find this information useful. These are tubes whoe's mate got broken or went bad ..ect... I was trying to find one that would work in a pinch with one I've been running in a 50 watt Marshall Jubilee. The set I've been running used to be a pair, but one has been drifting away and now they are 10ma apart. Too bad because this pair of =C= sound really good. Sweet and musical.

What I did was just leave the bias alone (running the good =C= at 38ma) and put the odd balls in one at time and measured their ma. The results are rather disconcerting because of the extremely wide range from 52ma all the way down to 10ma. No red plating was noticed. I did find two perfectly matching pairs believe it or not. One pair is a RTF Siemens and a Mullard! The other pair is a =C= and pre =C= Svetlanna (so they are both =C= but from different years) There were two tubes that didn't match fairly close anything. These two are a Groove tubes labeled of unknown origin, and a pre JJ Tesla.

The tubes that ran cold made the amp sound really harsh, Even one of them. The treble was brittle and the mids grainy. Just really bright overall all of the sudden. I had to turn the presence down 0 to stand it. (I was using V30 too) Bass was tight though.

I decided to put in the =C= pair that matched up for now, rather than burn up the Mullard/Siemens match. At 70% plate dissapation this pair still made the amp sound bad and harsh. Way too bright. I tryed it at 65% and didn't sound as bad, but still not real good. I finnally found a good spot and the amp started sounding great (through the V30 too), but it was 77% plate dissapation by then. I don't really care if this pair don't live a long life, as they come from the odd balls anyway. I'll take the tone. I really didn't notice much difference in loudness between extremely cold and hot bias, but there were huge differences in tone quality. Hotter bias gave more bass but it got progressively less tight. At the spot I left it, the bass was still tight enough for me.

 

[wixedmords]

Re: Testing EL34's

I don't think I would have done much different there LPB.

I likely would have searched for a good sound under 70% dissipation, but I understand your thinking. I might have swapped some tube positions to see if I could have gotten under 70%. I'd go for a little more reliability because Murpy's Law strikes me a lot taking tubes down at inopportune times.

Sometimes I like having a mix of brands in an amp, but I again try to stay away from max dissipation. One of my favorite amps I am playing right now, a AOR 30 has mixed brand tubes in it.

I think it is great you found a usable pair. More singles will be along and more pairs can be had in the future using this method.

Good post btw.

 

[TwilightOdyssey]

Re: Testing EL34's

Ah, tube rolling. Great way to while away the hours. And spend lots of cash!!

 

[Gearjoneser]

Re: Testing EL34's

When did you get a 50W Jubilee? Cool amp huh?

I think mine is biased at 38mA too. It seems best right around there.

By luck, I still had some of the original Siemens EL-34's from 1987 that were still perfectly good. Those came out of my old 100W Jubilee I had in the 80's. In 1990, I blew 1, and kept the other 3 in my parts drawer. Surprisingly, I compared the NOS Siemens, which Jubilees shipped with to a new JJ E-34L duet, and the JJ's won.
I have Sovtek LPS for pre's.

 

[Lake Placid Blues]

Re: Testing EL34's

I've had it since the 80's. I just got fed up with the rig I had one day and just spent a whole day going from one place to another and plugging into any and everything tube. When I plugged into that one that was it. I bought it right there. About ten years later I bought a used silver 4x12 to go with it looks wise. I also have the 1x12 combo version. These are cool amps. And very versatile. You can play just about anything and sound good doing it.