New EH 6CA7 idle hum issues

[R ski]

So I read positive testimonials regarding the sonic benefits of a 6CA7 power tube in contrast to EL34 and purchased a pair. Much to my disappointment, these tubes are not quiet at idle conditions, unlike any tube I tried before. They were set at 35MA per tube and the plate voltage sits at 460 VDC.

So I searched for information on the web, someone mentioned that pin 1 and 8 should be tied together, in which they are, although the EH data sheet does not show a pin-out, I looked at the physical connections on these tubes and pin one is connected.

Any ideas?

[Glowing Glass]

Personally, i had GREAT experience with my EH6ca7 set.

Bought a pair for my marshall 50wt plexi clone (ceriatone) and IMEDIATELY noticed 2 things.......... .

ONE, the tone i was looking for was there. Spot on!! For this particular amp, i was looking for a certain tone, like pete townsend-sh type british 60s hiwatts and marshalls had. Pete said a lot of guys used them in britain instead of the standard type el34. When asked by someone why they cant get that sound i tell them to switch to the 6ca7.

I also installed a set of EH 12ax7's with it. I cant stand JJ 12ax7 tubes. There is an unpleasant grit in them i hate. My amp came with those. I imediately replaced them tung-sol which i use a lot in my tube amps. So, after playing a while i pulled the EH set out and put my tung-sol 12ax7's back in for comparison. The tone i wanted was still there. A great combination with the tung-sol 12ax7's!! However, after a good 45 minutes, i put the EH set back in and they just have this real "musical" tighter sound. Just gave the amp that "sweet spot".Not super smooth like the Tung's and no nasty/fuzzy grit like the JJ's. The EH's are right in between, more dimentional. So i HIGHLY recomend that EH set up of 6ca7's and 12ax7's for anyones marshall or hiwatt.

TWO: Quite as a mouse at idle.

I would think in my non electronics engineering way that you may have a faulty tube. Both guys i talked into buying the EH set i use said the same thing, they loved the tone and were surprised at how quiet they were.

NOTE: Edward VanHalen has said recently, and his original tech had mentioned it (pissing off ed as it was during his dont give away ANY secrets period) that he used Sylvania 6ca7 tubes in his original "brown sound" plexi marshall. Not long before VH went in to record their first album, ed was in a vintage shop in so-cal and PETE TOWNSEND is there!! Ed is the one who asked him why his marshall didnt sound like his british guitar favorites did and thats when pete told him to try the 6ca7 tubes. As ed himself said, right off the bat, i heard the tone "missing" from the el34's in his plexi.

I had switched my set 2 years before i read the article with ed telling about his 6ca7 conversion. I had heard guys talk before about using those to get the REAL marshall/hiwatt tones of those brit players but as soon as i read that article i knew right away where that knowledge came from. Through pete, to ed.

Anyhow, probably didnt help you much, but i thought you might like hearing from another 6ca7 user and the cool pete/edward story.

[Amp Kat]

If pin 1 is internally connected to pin 8 than they aren't 6CA7's, they are tetrodes. A true Pentode has pin 1 isolated by itself. Most tubes these days are not tested either although they will tell you that they are but with the high number of lots and competition they simply don't have time or money to test them so it's possible you just have some noisy tubes or hopefully just 1 maybe.

[potatofarmer]

It would be great to get some definitive answers about 6CA7 tubes because I can only find conflicting information.

Old 6CA7 datasheets confirm that it's just the american designation for an EL34; the graphs clearly show no defined knee like you'd see for a beam tetrode.

Yet some people around the net claim that some manufacturer or another made a batch or two (or all of them) as beam tetrodes, again, back-in-the-day, as it were.

Modern production tubes, who even knows. I'm starting to suspect that a curve tracer is necessary for any certainty about what manufacturer X is selling as brand Y type Z, and if it's any different from manufacturer X's other brands A, B, and C as types D, E, or F.

Noise, however, seems like an entirely different issue anyway. What sort of noise- hum, buzz, etc? What's the amp?

[Leo_Gnardo]

It would be great to get some definitive answers about 6CA7 tubes because I can only find conflicting information.

Old 6CA7 datasheets confirm that it's just the american designation for an EL34; the graphs clearly show no defined knee like you'd see for a beam tetrode.

It's evident, just by LOOKING at a 6CA7, that it's a beam power tube. There's no suppressor grid; there are beam forming plates. It appears it was developed (in part) to be a sub for EL34, and there the confusion begins. Many tubes were marked with both designations, although they act & sound differently. 6CA7 bias voltage is about the same as EL34, from there they diverge. One thing I'm still not clear on, in 6CA7 is pin 1 connected to the beam plates? Or is pin 8 internally connected to both cathode & beam plates as in most other beam power tubes? May have to put the hammer to one if I can't squint thru the glass & see it clearly. I'll select a dead one for the hammer, unless someone else has the definitive answer.

[g1]

I would think that modern manufacture 6CA7 are just re-labelled EL34. Sort of like the modern 7025 is to 12AX7, just marketing.
I'd love to be wrong on this though.

[Leo_Gnardo]

I would think that modern manufacture 6CA7 are just re-labelled EL34. Sort of like the modern 7025 is to 12AX7, just marketing.
I'd love to be wrong on this though.

The EH 6CA7's I've used look distinctly different from EL34, and it's not just skinny glass / fat glass. I have no JJ 6CA7 on hand to look at. Will peer inside my EH's later today, let ya know what I see.

One customer noted a difference in tone/feel with EH 6CA7 in his Orange OR120. Wasn't much liking it either, and I wasn't much liking the idea of sacrificing EL34's to the Orange beast.

[Leo_Gnardo]

The EH 6CA7's I've used look distinctly different from EL34, and it's not just skinny glass / fat glass. I have no JJ 6CA7 on hand to look at. Will peer inside my EH's later today, let ya know what I see.

One customer noted a difference in tone/feel with EH 6CA7 in his Orange OR120. Wasn't much liking it either, and I wasn't much liking the idea of sacrificing EL34's to the Orange beast.

Revise that last one, I DO have a quad of JJ 6CA7. They definitely have beam forming plates. And those beam formers are connected to pin 1.

Other brands, we'll have to look.

Sylvania made the tough 6CA7's back in the 70's - wide bottles like 6L6's - with sloppy looking spot welds on the plates but they worked great in spite of that.