Hi fi build issues, i.e. looking for reliable EL84

[Synchu]

Some months ago I built couple of EL84 PP Class A monoblocks for my brother (very nice design by Bruce Heran. Can be seen @ http://diyaudioprojects.com/Tubes/EL84-Mini-Block-Amps/ - very interesting power supply approach, btw.). After these, I wouldn't foresee myself doing a hi fi project any time soon

Now, as recommended, I got couple of matched pairs of JJ EL84, which played fine for the testing and some time after.
Then some weeks ago I got call that one of the amps behaves strangely. Starts playing fine and then after some playing time (5-7 minutes) starts to loose bandwidth, bass gets flubby etc.
Going to his place with a DMM, the problem (or at least what I think is the problem) was easy to identify .

After some warm up time one of the tubes starts pulling considerably more current - starting from 41mA, i.e. the recommended bias value as set, it goes up to 60mA, while the other tube drops proportionally.
We tested the pair in the other monoblock - and the behaviour was the same.

I collected the problematic pair and ran them through my tube tester. One of the tubes tests fine, the other seems to develop oscillations (the tester measures Ia and for the problematic tube it doesn't show stable measurement - it varies constantly +/- 4mA and in between, which points me to the said oscillation issue).

He, meanwhile, got a new pair of JJ EL84s, that however developed the same symptoms and that I am going to run through the tube tester, but we would probably go for another make as my experience with JJs in the recent months has been less than satisfactory (few bad pre, bad EL34s, rattling 5U4, etc.... - all were tested, matched, selected whatever).

So, I am looking for recommendations on good and reliable EL84s. I already ordered some NOS Russian equivalents, but would like to point my brother to a more reliable (and easier to reach for non tech savvy person) new production tubes for the future.

Niki

[matt h]

(deleted)

[Structo]

Have you tried Eurotubes for the JJ's?

They only sell JJ tubes so he is able to focus on that.
He burns them in and matches them.

Located in Portland, OR.

http://www.eurotubes.com/store/pc/home.asp

[Synchu]

Thanks for the replies.
I used to purchase through a friend from Eurotubes, but now it is much cheaper (though might not be at the end ) to purchase from Europe, since the shipping and customs duties will at least double the price per tube.

The OT is ultralinear and screens are connected to the UL taps of the transformer. LM317 is CCS with quite a low voltage across it. I don't remember the inrush current/voltage measurements, but those stayed quite low and didn't cause me any worries.
We did flipping of the pairs between the amps and amps+bad tubes behaviour was consistent - 5 minutes playing good then the described behavior happens.

It might be something of the design, but there are quite a few people that did these amps and no one reported a single problem.

It is a very good point though, I was thinking of this as well.
Might get the amps opened and measure those suckers (and replace them with a hefty 25 watt cathode resistor ala Trainwreck and be done with all this hi fi complications once and for all )

Tubes had been purchased from banzaimusic and one pair from a local shop here. Banzai have great choice, pricing and albeit lately some problems with inconsistencies in stock indicators at the online shop, causing me waiting few weeks on backorders, they've been rather reliable vendor. I don't know who does the matching for them and if testing is done and how, but everything else, besides the mentioned various failed JJ types above, was just fine (within the current production terms of reference or lack of them thereof )....

Niki

[matt h]

(deleted)

[billyz]

Try some sovtek el84m . They have been my go to el84 for years. I am not a fan of el84's in general, due to reliability issues. But the el84m have been the most reliable of all the modern tubes of this type in my experience.

Also known as 6n14n-EB.

[Synchu]

Getting the point on the screens. But I rather run it through the scope first, before getting an eternal curse from the hi fi crowd

Yep - same tube crapped, did the swapping on the same monoblock and on the other.

I am far from the idea that I did everything as it should be, but they worked fine for some time (and sound great - I wasn't that much believer - you know - guitar player - tube amps are for big loud overdrive, but these monoblocks do smash down the not-so-bad SS receiver my brother used - they do sound MUCH better).

EDIT: billyz - thanks for the note, I already ordered some NOS 6P14P-EV glass yesterday. I never had any issues with this old russian tubes and I am using and abusing 6V6 and 6L6 equivalents quite a lot. I never liked EL84s in a guitar amp through the years (until I joined ampgarage and heard a TW Rocket sample ) and never used them. I guess current production Sovteks should be quite close to these.

Great thoughts, keep them coming.

Niki

[David Root]

I wouldn't agree that current production Sovteks would be the equal of rhe NOS 6P14P-EV. Those are ~30 years old Soviet milspec tubes, a different animal, and are the only EL84s I would ever use, other than maybe NOS Telefunkens, even if I liked EL84s.

But like billyz I'm not a big EL84 fan.

[gingertube]

Never had problems with JJ EL84s.
BUT - I don't like self spit or common to both push pull sides bias schemes.

I have an EL84 Push Pull HiFi design which has been made into a Wiki here:
http://www.diyaudio.com/wiki/Baby_Huey_ ... _amplifier

Lots of these been made by folks all round the world. The forced balance scheme works really well and is the best sounding PP EL84 Amp I've ever built or heard.

The prototype of this amp was originally a Morgan Jones "Bevois Valley". Rebuilding to this scheme was a definite step up in performance.

The current source bias scheme is good BUT it has crap overdrive characteristics which make it an unsuitable circuit for a git amp.

There is a Baby Huey thread which includes some fixed bias variations.
What I'm now running at home is the schematics on posts #602 and #603 here:
http://www.diyaudio.com/forums/tubes-va ... ey-61.html
Post #604 schematic variation is something I tried for a while but eventually abandonned.

Hope these are of interest.
Cheers,
Ian

[matt h]

(deleted)

[Stevem]

If you have a 4 output tube deal and do not mind having two different cathode resistors , or in fixed bias two differing voltage setting than running two 6973s and two EL84s makes for a fine sound!

[Synchu]

Quick update FWIW.
It has been tubes related after all.
Never got the NOS russian glass, unfortunately. Some problems with the delivery (~4 weeks waiting), but I did get prompt refund on that.

This aside, I got a set of EH EL84 (since my bro was a bit impatient) - biased perfectly and perform great.
JJs sound was slightly better (while they worked), but EHs are far better in terms of reliability and as it seems consistency.

An issue though is that I am now left with a bunch of JJ EL84, seemingly not good enough for hi fi, but should be good for a guitar amp (or two to be precise). Will have to build something around them...

Niki