Modern EL34 reliability?

[Gregg]

Last time I ordered the 4xJJ EL34 and one of them failed after a year or so. Currently in the same amp I have 4xJJ EL34 II tubes which are different "īmproved" version of their regular EL34s which bias properly at more negative voltages. We'll see how long they'll last.

[Gregg]

Looking at the date of my last post it turns out that those JJ EL34 II lasted less than a year after a very moderate use. One of them became very microphonic and developed erratic behavior currentwise (going up to +100mA). "Knocking" tests on the chassis and on the tubes caused sparks inside the tube which brought my tests to an end.
Plate voltage was 475V. I used zeners to lower the screen voltage down to 445V. The tubes were moderately fan cooled. Other than that tubes' sound was good.
In the same time two of the tube from the JJ EL34 set are still working in another amp and I'm retubing an amp that had two of the same type installed and that was used every week for couple of hours for two years which looks like a hit and miss situation.
Now I'm wondering whether to try a JJ 6CA7 or to go for Chinese EL34B. I see also some EL34BW for sale but can't find any opinions on those.

[tubeswell]

Looking at the date of my last post it turns out that those JJ EL34 II lasted less than a year after a very moderate use. One of them became very microphonic and developed erratic behavior currentwise (going up to +100mA). "Knocking" tests on the chassis and on the tubes caused sparks inside the tube which brought my tests to an end.
Plate voltage was 475V. I used zeners to lower the screen voltage down to 445V. The tubes were moderately fan cooled. Other than that tubes' sound was good.
In the same time two of the tube from the JJ EL34 set are still working in another amp and I'm retubing an amp that had two of the same type installed and that was used every week for couple of hours for two years which looks like a hit and miss situation.
Now I'm wondering whether to try a JJ 6CA7 or to go for Chinese EL34B. I see also some EL34BW for sale but can't find any opinions on those.

Go Chinese (if your government hasn’t banned Chinese imports yet &#128577. They seem to be robust.

Treat them as 20W tubes (= bias them cooler).

Be wary of customers who run their amps through power attenuators.

No point in replacing pairs in a quad of EL34s IMO. You want the whole quad to be matched, especially at those voltages. Otherwise the current will pick the path of least resistance when the amp is cranked (which will be the pair that runs hotter)

YMMV

[catalin gramada]

I running for month Tung Sol el34b with 490v into screen grids and common 220k grid leak for a pair , biased pretty high (75 percent around) into 1.9k OT .No sign it will given up.

[drewl]

I've always had problems with JJ's of all type.

I have used a Hotplate with my own Marshalls with EH EL34's with no failures.

[Diablo]

Hate to bring more bad news, but according to Shuguang, their EL34B tubes are tetrodes, not pentodes.
Their EL34A was a pentode, but was discontinued, likely because of problems with reliability.

[tubeswell]

Hate to bring more bad news, but according to Shuguang, their EL34B tubes are tetrodes, not pentodes.
Their EL34A was a pentode, but was discontinued, likely because of problems with reliability.

so more like a 6CA7 or a KT77 then?

[Diablo]

so more like a 6CA7 or a KT77 then?

Yes, some folks claim that the EL34B and KT77 have the same internal parts. I don’t know if that’s true or not.
I do know that The Shuguang EL34B tubes sound a lot different (and better) than NOS 6L6GC tubes in my Tweed Twin 5E8A clone. Less emphasis on high frequency and more on midrange. I originally thought it was because it was a pentode, whoops wrong.

[Helmholtz]

It should be possible to tell a pentode from a beam tetrode by dissecting a (defective) tube and see if it has beam confining/reflecting plates or a third (suppressor) grid.

[Chuck H]

It should be possible to tell a pentode from a beam tetrode by dissecting a (defective) tube and see if it has beam confining/reflecting plates or a third (suppressor) grid.

I have a couple of pairs of this tube. I had to buy three pairs to get one that wasn't too microphonic to use in a combo amp project So these ones are a bit too microphonic for combo amp use but I'm saving them in case I can ever use them in a head amp. A local customer has the least microphonic pair, but he doesn't use the amp much. Not sure what my point is except that I have this tube on hand and if one ever dies I'll open it up for look.

[Pedro Vecino]

I have counted three grids...

[Helmholtz]

I have counted three grids...

[ATTACH=CONFIG]56345[/ATTACH]

So pentode.

[Chuck H]

So why does Shuguang think it's a tetrode

[Helmholtz]

So why does Shuguang think it's a tetrode

Good question, provided we are speaking of the same tube.

The whole story seems obscure to me. I mean, why should a manufacturer give his tetrode the name of a classic pentode? Tetrodes and pentodes can't have exact same charts: different curvatures and screen currents.

If the EL34B actually was a tetrode and behaves like a KT77, why not call it a KT77?
(IMO, the KT77 is the more advanced design.)

[Enzo]

Or someone made an error.

According to the Shuguang web site the EL34B is a pentode. They make that and the EL156. Their listing of beam tetrodes does not contain any EL34 types.

http://shuguangtube.com/e_products/?big_id=1&small_id=7