Cathode follower driven RT-66 tone stack?

[Dingleberry]

Hi.

I was just wondering that could that particular Dr.Z tone stack work well when driven by 12ax7 cathode follower instead off ef86 plate?
Would the low source impedance affect somehow to the sound, or would it be more than ok? Would one have to scale down the values or will it work like it should?

-T

[tubeswell]

The high output impedance of the EF86 does take the high end out of the bandwidth - even in the Route 666. A CF helps preserve the bandwidth, plus there's the added bonus that the low plate voltage of an EF86 when DC-coupled to a CF, results in being able to have a lower h-k voltage in the CF stage (which is good for modern 12AX7 longevity).

But a CF with an EF86 also allows a another possibility, namely using the CF cathode to drive the type of triode-pentode morph control Merlin put in his first book (and in the 2nd edition)*. Hook the blocking cap on the input side of the morph control to the CF cathode instead of feeding the input side of the morph control from the EF86 plate. This not only enables the morph control to be driven from a low output impedance, but also stops the morph control from loading the EF86!

(* Merlin however didn't put the CF-driven morph control in his book - that idea came from somewhere else).

[tubeswell]

Here's a pic of what I mean (This is using a 5879 driver)

[img:575:339]http://farm9.staticflickr.com/8192/8381 ... 3e81_z.jpg[/img]

[Dingleberry]

Thanks for the tip Tubeswell!
That looks well worth experiencing.

I forgot to mention that I wasn't using EF86 at all in this project.
I have the preamp wired like a 5F6A/JTM-style (2x12AX7) at the moment.
Sorry about that confusion. English is not my native language so sometimes my writing can leave a little more room for misconception that I originally meant to.

I have an EF86 project coming (hopefully before summer) so then I will came back to that schematic.

I tried that RT66 tone stack and it sounded ok, nothing spectacular. Then I wired it to james tone stack and got kind of same results. Last thing I did was to add a middle cut control (from Merlin's book "Matchless"-style) right after first gain stage, before volume pot and got slighly better results. Anyhow neither of those sounded keepers when volume turned past breakup. Cleans were beautiful though and wide variety of sounds available.

I think that I wire it like old Marshall and start tuning it from there, if it don't satisfy me. I've always wanted a good 50W JTM/JMP anyway;)

I find it wery educating to experience with these things and you really practice your ears and learn to trust them more. For them we are building these amps anyway aren't we?

-T

[M Fowler]

This schematic was posted years ago. It uses a 12AX7 preamp tube and non-UL OT.

I first built my Route 666 with EF86 and JTM45 iron also but since then installed Hammond iron so I could have UL taps. I actually like the JTM45 iron better

Mark

[andrewx]

Hi, refering to Tubeswell's diagram what is a good tone control to go into a driver/cathodyne phase inverter? The diagram stops at 1000pf. Thanks for any help.

[TUBEDUDE]

This schematic was posted years ago. It uses a 12AX7 preamp tube and non-UL OT.

I first built my Route 666 with EF86 and JTM45 iron also but since then installed Hammond iron so I could have UL taps. I actually like the JTM45 iron better

Mark

In pentode mode, with the Hammond UL disconnected, it should sound pretty good.

[Reeltarded]

Mark! UL is the Devil!

Gahhh!