The elctro harmonix 6CA7 is not a real 6CA7.
It's a relabeled tube, but who knows which tube it really is.
A real 6CA7 is a pentode.
The EH 6CA7 is a tetrode.
Just a heads up.
Electro-harmonix has been pulling a lot of substitutions and re-labeling of tubes....
Traynor Amps:
DO NOT plug an electro harmonix 6CA7 into a Traynor amp.
You will short out your bias power supply and damage the amp.
Just a word of warning.
There is a lot of confusion & missinformation regarding exactly what makes for a "true" 6CA7 (which, by the way, the EH 6CA7 actually "is"), especially among people who have never actually used old production USA made 6CA7's as designed by Sylvania.
So let's go back in time & get to the bottom of it shall we.
So, Philips (Mullard) designed & patented the pentode. A pentode has 5 electrodes, being a cathode, control grid, screen grid, suppressor grid & anode (aka plate). Anyone using this fabulous "pentode" design had to pay Philips a royalty.
The MO Valve company (MO = Marconi Osram) set about to design a new valve type to avoid paying royalties to Philips.
The design that they came up with did away with the "suppressor" grid. Rather, it used "beam forming plates" to focus the electron stream into a narrow "beam" that had the effect of greatly reducing secondary emission (electrons bouncing "back" off the plate), the very same thing that the suppressor grid was designed to do in a pentode.
The MO Valve company called this newly designed tube a "beam tetrode" & in an info sharing arrangement with US valve manufacturers, shared the technological design info.
The MO Valve company further used precise alignment of the control grid & screen grid wires & manipulated the plate structure of the "beam tetrode" to produce what is known as the "kinkless tetrode". The KT66, KT77, KT88 are among these (KT = kinkless tetrode). The MO Valve company DID NOT share this info with manufacturers in the USA.
Back to the 6CA7. Sylvania utilised the MO Valve companies "beam forming plates" technology to design & produce the 6CA7, seen here
Commonly known as a "fat bottle" or "fat boy" 6CA7.
To summarise, the pentode, which contains a suppressor grid, was patented. The "beam tetrode", which does not contain a suppressor grid, was designed to avoid paying "pentode" royalties. The "true" 6CA7 has beam forming plates & no suppressor grid, therefore is a "beam tetrode".
Now we see a lot of talk about the beam forming plates being "electrodes" inside the valve so it has to be a pentode, but I'm sure the design engineers at the MO Valve company who designed the freaking "beam tetrode" valve type knew maybe just a little more than these armchair valve commentators calling it a pentode,,, so I'll take the designers word on what it is.
The 6CA7 is an acceptable substitute for the EL34 in many applications, even though one is a beam tetrode while the other is a pentode, however it is not an acceptable substitute in some designs (where there is a negative voltage applied to the pentode's suppressor grid, for example).
No you can't plug the EH 6CA7 into your Traynor amp (unless it's first modified to allow it).
You also can't plug an original US made Sylvania, RCA or GE 6CA7 into your Traynor amp either, unless it's first modified to allow it.
You can plug a JJ 6CA7 into your Traynor amp though, as the JJ 6CA7 isn't a true 6CA7, rather, a "pentode" design. Cheers
