2 Cathode Followers on the same tube?

[dsmith9]

I'm building an amp that will have 2 cathode followers.  One to drive the tonestack (ala Bassman), the other as part of a Dumbleator-like buffered effects loop.  For layout reasons it would be most convenient if I could put both of the CFs on the same tube.  (The amp is cathode-biased, so I can elevate the heaters using the power tube cathode.)
 
Is this a bad idea?

Thanks

[sluckey]

no

[pdf64]

I don’t see the point of the CF in the dumblator and similar fx loop?
As the 250k send level pot that it feeds will, at most settings, raise the source impedance of the send jack by an order of magnitude or 2 above the low impedance that the CF provides.

[tubeswell]

In terms of ^what pdf64 said^, you can take the CF send from an unbypassed cathode on one of the gain stages. It will have a low output impedance, and won't slam the input of the FX device, and it frees up a triode.

[dsmith9]

@pdf64, Great point.  Effects loops driven by a CF seem to be pretty standard.  I never thought about the fact that the Send pot defeats the low-impedance point of the CF.  Makes you wonder why that design is so popular.

@tubeswell, that's a really interesting design.  Is the reason for tapping the cathode instead of the plate to maintain phase, since it's a parallel loop?  Is there a longer discussion of this design in a thread somewhere that I could read to educate myself?

Thanks guys.  Gives me something to think about.

[tubeswell]

@tubeswell, that's a really interesting design.  Is the reason for tapping the cathode instead of the plate to maintain phase, since it's a parallel loop?  Is there a longer discussion of this design in a thread somewhere that I could read to educate myself?

Yep its to maintain phase for FX loops that maintain phase. There's no discussion of this design anywhere - I just knocked up a schematic.