DC cathode follower with separate tubes

[maxkracht]

I am laying out an amp with a DC coupled cathode follower where it would make more sense to use two separate tubes instead of both in the same envelope. I can't think of a reason why having the gain stage in a separate bottle from the follower stage would be a problem, but I don't know if I have ever seen it done this way. Any pitfalls I should look out for?

[Stevem]

Please explain why in your scratch build that such makes more sense?

What circuit are you driving with the followers output?

I don’t see what you want to do as being an issue as long as the down stream wire run to the second stage of the follower is no longer than like 2”.
One other thing to note is that a cathode follower set up produces no gain, in fact it’s output is less then it’s input to its first section.
What you get out signal voltage wise will always be about 20 to 25% less then what goes into its first section.

[Ten Over]

I am laying out an amp with a DC coupled cathode follower where it would make more sense to use two separate tubes instead of both in the same envelope. I can't think of a reason why having the gain stage in a separate bottle from the follower stage would be a problem, but I don't know if I have ever seen it done this way. Any pitfalls I should look out for?

I have done it several times. I put a resistor and a diode between the grid and the cathode of the cathode follower, so I'm coming back to the board between the gain stage and the cathode follower, anyways.

[TUBEDUDE]

I've used half a 12DW7 as a cathode follower after a 5879 pentode with no issues.

[maxkracht]

lease explain why in your scratch build that such makes more sense?

Building into a vibrochamp chassis, planning to try out Slucky's Trem-O-Nator for one triode. Tremolo controls are closer to power tube, will probably use the screen node for power, so everything tremolo is on one side of the amp.

What circuit are you driving with the followers output?

CF driving a FMV tone stack then to the SE 6v6 output. The plan is 5f6a topology for the preamp but I'm open to ideas if this seems silly. Using the other half of v1 would probably work about as well, just slightly longer wire runs.

I've used half a 12DW7 as a cathode follower after a 5879 pentode with no issues.

This project also had me thinking of doing something similar, nice to hear it works.

[TUBEDUDE]

lease explain why in your scratch build that such makes more sense?

Building into a vibrochamp chassis, planning to try out Slucky's Trem-O-Nator for one triode. Tremolo controls are closer to power tube, will probably use the screen node for power, so everything tremolo is on one side of the amp.

What circuit are you driving with the followers output?

CF driving a FMV tone stack then to the SE 6v6 output. The plan is 5f6a topology for the preamp but I'm open to ideas if this seems silly. Using the other half of v1 would probably work about as well, just slightly longer wire runs.

I've used half a 12DW7 as a cathode follower after a 5879 pentode with no issues.

This project also had me thinking of doing something similar, nice to hear it works.

Just make sure they are both tied to the same power supply node.

[Mark]

I built a Trainwreck Rocket and the gain stage and the cathode follower are different valves. I didn’t encounter any problems.

[maxkracht]

Just make sure they are both tied to the same power supply node.

yep, not doing anything crazy. V1a > volume > V1b +V2a cathode follower > tone stack > V2b tremolo

The first triode stage and CF stage will get their own power supply nodes. Probably unnecessary, but just enough room for two 8uf film caps on the main board. Stack of taller 18uf film caps off of the board for a CLC filter before the 6v6.

[maxkracht]

I built a Trainwreck Rocket and the gain stage and the cathode follower are different valves. I didn’t encounter any problems.

Not sure how I missed that one. Any idea why it was laid out this way, with the unused triode on v2 instead of leaving an unused triode on v1 and using all of v2? That, along with an unused triode in general hurts the obsessive part of my brain...

[Mark]

I wondered about that too. I considered running the triodes in parallel, but in the end I added the Blencowe cathode follower mods.

[maxkracht]

Worked out fine. First amp i've built with ALL film caps, was a fun design exercise. Trem-o-nator is cool. Tried wiggling the 6v6 grid leak and the volume pot, volume pot won. I also played with wiggling the negative feedback loop, also NFB plus the volume pot with another opto which is kinda interesting. I'm sure there are potential stability issues, and probably other problems, but worked fine on this amp. Kind of a fun character, wonder if anyone else has tried that.