6973 in Place of 6V6

[Chuck H]

Yeah, OK, but who decided that the beam forming plate doesn't count as an electrode? It's connected to a specific potential (same as cathode, just like suppressor grid.) It influences the trajectory of the electrons due to it being at cathode potential. Why is it not considered an electrode?

Pretty much agree with this on a semantic level, BUT... In science (and I think most technologies qualify as sciences) the original name for a given aspect (species, genre, genome, compound, etc.) is supposed to be used to the exclusion of absolute accuracy in the interest of provenance, referencing historic data and further study. In that light if the original name given to the design was beam tetrode then it should be used. I don't think those tubes with the moniker "beam pentode" from the manufacturer differ in operation significantly from previous designs called "beam tetrode. That doesn't mean the design ISN'T a beam pentode, it just means it's not called that.

Just playing devils advocate now.

[Tony Bones]

Pretty much agree with this on a semantic level, BUT... In science (and I think most technologies qualify as sciences) the original name for a given aspect (species, genre, genome, compound, etc.) is supposed to be used to the exclusion of absolute accuracy in the interest of provenance, referencing historic data and further study. In that light if the original name given to the design was beam tetrode then it should be used. I don't think those tubes with the moniker "beam pentode" from the manufacturer differ in operation significantly from previous designs called "beam tetrode. That doesn't mean the design ISN'T a beam pentode, it just means it's not called that.

Just playing devils advocate now.

I think GEC invented them and they originally called them Kinkless Tetrode, hence KT-66...

Whatever. I may call them Pentodes from time to time if I feel like it, in the same way that I sometimes use an uppercase "K" for kilo. Come at me soundmasterg!

[Justin Thomas]

Another for Justin because he sacrificed a tube. I almost did it because I do have a pair of pulls... But it IS a pair and I've never tested them. If they're good I'd have hated to waste them.

EDIT: Actually, Justin said he used his phone flashlight.?. But I guess I'm uncertain if he just used it to look into the tube or smash it open

I DID NOT SMASH A WORKING VINTAGE RCA 7591A!!! Just so we are all clear. As far as whether it's a beam tetrode or pentode, well, I've seen some really funky $#!+€ in old tube manuals. I see 5 active elements in it. I also see tube diagrams where the yube is listed as a beam tetrode. I also see listings for beam triodes too. I shite you not. I've gone through RC30 plenty of gimes & I trust them...

Whether it's a tetrode or a pentode, it curves like a pent & has 5 elements. As far as GEC & the KTseries, I don't remember which came firstbut as I understand it one was an answer to the other, without having to do a radical retool of the factory.

Justin

[g1]

The 6CA7 is similar to the EL34 but is a beam tetrode.

To further muddy the waters on the 6CA7 particularly, it seems there is a MkI and a MkII, the original skinny bottle type being a pentode with an american version numbering. Someone (philips ?) came out with a 'beam type' in the larger 6L6 style bottle. The beam type being preferred, and sometimes erroneously referred to as a 'real' 6CA7 when the skinny pentode is also a valid example.

[soundmasterg]

I believe that GEC invented the kinkless tetrodes to get around a Phillips patent on the pentode design, but they initially had trouble with it, so since they were affiliated with RCA in the uSA, they forwarded the design to RCA who then made the 6L6 and the rest is history.

Names do matter because beam tetrodes have better high frequency response than pentodes as a general rule, so if you were a designer of an amp you have to take that into account with your circuit and your layout. If someone tells you it is a pentode and it really is a beam tetrode and you don't take that into account and design your amp assuming it is a pentode, then you could run into problems. It probably makes more of a difference with beam tetrodes that are used for RF rather than the 6L6 per se, but anyway, that is the gist of what I was able to discover on the difference in the naming. At the end of the day, even though the beam forming plate might be considered another electrode by some, that design with beam forming plates is not the same as a traditional pentode with a suppressor grid and they don't behave the same either. So as I said, names do matter to avoid confusion.

g1 thanks for the heads up on 6CA7 history. I only know about these in general but it doesn't surprise me that they made both versions. I prefer the EL34 to it in most applications, and also the KT77, but any old stock 6CA7 will be better than what we have today!

Greg

[nosaj]

Here's some more info on the subject
https://en.wikipedia.org/wiki/KT66
nosaj

[soundmasterg]

And some more info here.

https://en.wikipedia.org/wiki/6L6

Greg