I don't know if any of you guys have tried these yet, but I just got a quad.
I tried them in a 1971 DR103 immediately after playing the amp with a set of JJ E34L's.
Initially the amp is louder with more bass. I only had a few minutes to try them, but I will post more impressions later.
They appear to be a rugged tube. pictured next to a Mullard XF2.
I have a set of NOS Sylvania 6CA7s that sound KILLER in a DR103. It'd be cool if the JJs were built similar to the originals.
The 6CA7 was a large and rugged US EL34 clone, using beam plates to get around Mullard's screen grid patent. Other notable beam power tubes include the 6L6 and KT77. The beam tetrode is more efficient than a true pentode, because you don't have to supply the screen current of a pentode like the EL34 (about 10% of the plate current).
Mark, I think you are wrong. Beam tetrodes have the same screen grid (second grid) as pentodes, the difference is between third grid, pentodes have true grid, while beam tetrodes have beam forming plate instead of true grid.
The beam power feature replaces the suppressor grid, so while the tube functions similar to a pentode, it remains a tetrode. The suppressor grid functions at ground potential, so it shouldn't affect the operation of a half-power switch.
As such, a 6CA7 is functionally comparable to an EL34, but isn't a clone either in construction or sound.
Popular beam power tubes for guitar amps include 6L6, 6CA7, 6550, and the entire kinkless tetrode (KT) series (KT66, KT77, and KT88).
You are both correct, of course. The suppressor grid is the replaced, patented feature. However, the beam tetrodes are still slightly more efficient than pentodes, all other things being equal.
My humble observations after a brief test drive of the JJ 6CA7's:
Dr.Hiwatt used the term "bold". I'd say "forward", "up-front", perhaps even "in your face" to describe the mid-range punch of these tubes. Not harsh, but very aggressive.
I'm sure these tubes will gain some fans. My particular tastes yesterday preferred EL34's "warmth" instead.
Other notable beam power tubes include the 6L6 and KT77. The beam tetrode is more efficient than a true pentode, because you don't have to supply the screen current of a pentode like the EL34 (about 10% of the plate current).
