tetrode or pentode??

[ironfly]

I'm a bit confused about the nature of 6ca7 tubes...is "6ca7" just another name for the el34 tube??
This is the opinion of the majority,but somebody says that el34s are power pentodes while 6ca7s are beam tetrodes (like 6L6s and 6550s)!
(To my ears,6ca7s sound tighter,less compressed than el34s...however,i don't feel this difference is such as to consider 6ca7s closer to the 6L6/6550 family!)
I wish somebody could clarify this point once for all!

[Old Tele man]

...6CA7 is USA identification for EL34...both are supposed to be true, 5-element, PENTODES.

...however, some eastern-europe tube manufacturers have been substituting beam tetrodes for EL34's because they're cheaper/easier to make...they're only "approximately" the same characteristics wise however.

[ironfly]

How do these european versions sound?

[Steve Conner]

EL34s are supposed to be actual pentodes.

The story behind this is that the EL34 and 6L6GC were rivals, in the context of a bigger battle between pentode and beam tetrode technology.

The EL34 won in Europe while the 6L6 conquered the States. The big bottle 6CA7 available in the States, AFAIK, was a tube designed to be compatible with EL34 sockets in an effort to tread on Philips and Mullard's turf, while sticking with the preferred beam tetrode technology.

6CA7s in a skinny bottle should be pentodes, though. I have a pair of Matsushita Electric 6CA7s that are true pentodes and look almost identical to Mullard EL34s.

[ironfly]

Have you ever tried the "fat bottle" 6CA7s?
I think they are tonally different than the skinny ones!

[Steve Conner]

That's what I just said. Fat bottle 6CA7s are beam tetrodes, skinny bottle ones are pentodes.

[Enzo]

How does one make this determination?

RCA calls their 6CA7 a power pentode and their 6L6 as a beam power tube, both in fat bottles. They show it as "6CA7/EL34."

GE calls their 6CA7 a power pentode and their 6L6 a beam power tube, both in fat bottles. They show it as a "6CA7/EL34."

My old Sylvania book (1959) lists 6CA7 as a beam power tube, and is in a fat bottle. However it also adds "Type 6CA7 is identical to type EL34." They also list 6L6 as a beam power tube.

I mention the 6L6 listings to show that these manuals do make a distinction between pentodes and beam tubes.

So I am not saying you are wrong, but it does not seem clear to me that we can make the blanket statement that EL34 is a pentode and 6CA7 is a beam tube.

This is all from the days of "real" tubes. In this day and age of sticking a 6L6 on a different base and calling it a 7027, perhaps some makers are selling beam tubes instead of pentodes.

[Alex R]

Hey, I have a worthless EH 6CA7 with shorts, came in a batch of good ones. Maybe we should take it to bits and see. Not that I'd know a beam forming plate from a suppressor grid, or from a hole in the ground for that matter.

[dai h.]

That's what I just said. Fat bottle 6CA7s are beam tetrodes, skinny bottle ones are pentodes.

not always. The GEC(General Electric Company of England) KT77 was a beam tube and not in a fat bottle like the American (GE and Sylvania) ones. Ei had one also.

My understanding was that "6CA7/EL34" was just a difference in American and European designation like "12AX7/ECC83". "6CA7" meaning specifically a fat bottle beam version is mostly something in popular usage by tubeheads, seems to me.

[ironfly]

Enzo mentioned the 7027 tube...what kind of tube was it?what did it sound like?most people say it's tonally similar to the 6l6 type...

[Old Tele man]

7027 is a "big brother" derivative of 6L6, ie: both are beam power pentodes.

...it has same "operating" characteristics as 6L6 (including filament current)...except for up-rated plate and screen dissipations.

[ironfly]

does it mean louder and cleaner?

[Enzo]

It had different base wiring. It was the tube Ampeg used for many years, and pretty much nobody else used them.

[ironfly]

thank you all for your replies