Parallel Preamp Design Help

[jjschessmaster]

Hey all!  I have a question that might seem silly to anyone who has ever designed an amp.  I've built a bunch of kits, followed some scratch built layouts, and have made benign mods (bright switches, depth mods, etc) but have not done much more than that.

I'm looking at building a tube town ac18 (just want to try out an ef86 ultimately).  The kit is based on an 18 watt chassis so it has a spare preamp spot and a few inputs and controls open.  I figured it would be relatively easy to toss in a parallel triode like the spitfire as a channel 2.  I would like to run it parallel with individual inputs.

Where would I tie the signal path in?  I've copied the link to the ac18 schematic and spitfire.  I think I disconnect the ground off the phase inverter c9 and plug in there?  Do I need to change c9 to 10nf?

Appreciate any help as I get my feet wet into more significant mods.

https://media.tubetown.net/cms/?DIY/18Plus/TT_AC18_-engl-

https://media.tubetown.net/cms/?DIY/18Plus/TT_Spit_F.

Edit; tried to fix Spit F. link, failed. 

[SEL49]

This may give you some ideas...

https://sluckeyamps.com/dual_lite/dual_lite.htm