Hey all,
I dug around before asking and came across the" EF86 Driving A TS" thread. But, has anyone used a EF86 to drive a cathode follower pre tone stack (ala 5F6A/Marshall)? What effect would that have on the tone(stack)? BTW, I only need one triode/pentode for the CF as it's a single channel build.
Can anyone recommend an alternative? On the other end of the spectrum I could cascade both sides of a 12AX7, but that'd be way over the top!
The issue with preamp pentodes is the high output impedance, thus using a cathode follower after the pentode alleviates this issue and provides a lower output impedance. You can also adjust the tone stack as suggested in that thread. It's a matter of what approach you want to take. Some don't like the affect of the CF on the pentode tone, but I tend to like it, but that's my personal preference.
That looks like a real mixed metaphor. The only real practical example of a
pentode/follower I've seen in a vintage piece was a reverb driver in an old Alamo.
Multiple tone controls usually end up more of a problem than a solution.
The gain structure is all over the place, a single pentode with high impedance
vol. tone will give more than enough gain placed in front of that type of inverter.
You can use a presence and resonance controls in a feedback loop to get the
addition tone/texture controls with out creating a monkey fist out of the pre.
I can see a pentode as the first stage, with half of say a 6sn7 or 12au7 used
as a follower, and then the other half as a buffer between the tone and inverter,
the pentode makes all the gain. If you used a 12ax7 and a master
volume you'd get predictable dirt. The pentode doesnt have to dressed as
a pentode, if your simply looking to color the tone with the tube type, a 6sj7
has separate G1, G2 and G3 pin out, and can be dressed in variety of ways.
