Help me understand Tube Z-Out

[Lonely Raven]

I'm researching output tubes for some projects I'm hoping to
finish (experiment). I'm reading up on the tube data and Z-out.

My short question, if a 6L6 is 5000 Ohms, are two of them
added up for 10,000 or divided for 2500?

Also, are 6V6 close enough Z to be used on an OT designed
for 6L6?

Part of why I'm researching this is that I'm finishing up a
Deluxe Reverb type thing, and I have a 50watt 6L6 Multi-Tap
OT I'm wondering if I can use for this build.

[Old Tele man]

actually the 6L6GC dynamic plate resistance (rp) is about 33K-ohms, and the "approximately" optimum plate load for a beam / pentode lies somewhere between 1/10th and 1/6th of the tubes' rp value...so, if we "split-the-difference" and use 1/8th of 33K-Ohm we get:

R.load = (33K/8) = 4,125 ~ 4.1K (2 x 6L6 OT)

...for a push-pull circuit, that'd be the Plate-to-Plate resistance (R.load = Rpp).

...but, when it's a parallel/push-pull circuit (like Twin, Showman, etc.), there're TWO tubes in parallel "...per side," or effectively, one-HALF of rp:

Rpp = (33K/8)/2 = 2,063 ~ 2.0K (4 x 6L6 OT)

rp = 50.0K for 6V6GTA, about 50% greater than 6L6GC...
rp = 15.0K for 6CA7/EL34, about 50% of 6L6GC...

[Lonely Raven]

Ahh, Ok, that makes sense then. Thanks OTM!

I was looking at Z-Out thinking that's what I needed to match,
but looking at the tube Data on Duncanamps it looks like I
should hav been looking at Ra.

Duncan Amps 6L6 Tube Data (http://tdsl.duncanamps.com/show.php?des=6L6)

I'm writing down this info for future reference.
This also helps me understand why when you swap tubes
from 6L6 to EL34 you are supposed to switch which output
tab on the OT to use.

That was one of my goals of things to understand so I could
pick through the OTs I have and find the correct one.

[Old Tele man]

as my daughter would say: "...correct-o-mundo..."

[Lonely Raven]

Thanks again Fonze! Er, I mean Tele!