I'd been using a 12AY7 in my Finally V2 lately (just a step up in gain from the stock 12AU7). A couple weeks ago at practice, I was messing around and wanted to see if it would have enough signal to drive the power stage of my head (Quilter BB802) on its own, so I stuck it into the effects return to bypass the preamp. I set the input gain on the head pretty low most of the time (just at 9 o'clock), but even with the Finally at max level the output was a fair bit quieter than going into head's preamp, and wouldn't really be a viable way for me to run it. I even double checked the internal trimpots of the pedal to make sure they weren't attenuating the outputs.
Around the same time I stumbled onto the 12DW7/JJ ECC832 - you get one high gain triode from the 12AX7/ECC8
3 and one low gain triode from the 12AU7/ECC8
2 in the same tube. JJ also makes the ECC823, which is the same triodes in reverse configuration.
One the things I've picked by hanging around this thread is that for designs like the Finally, Space Heater, Underground Accelerator, etc. is that one half of the tube controls amplification via the input gain, while the other controls the output level. Thankfully I'm not the first person in this thread to stumble across the 12DW7/ECC832 - and I managed to find a couple people asking about it, and even found this handy reply from the Sushi Master answering a question about hypothetically using a 12DW7 in a Handwired Underground Accelerator:
HWUA goes into the second tube stage (pins 6, 7, and 8) first, so with 12DW7 it would be like having a 12AX7 for the first stage and a 12AU7 for the second stage. ECC823 would be the opposite.
What I never turned up was the results of someone trying it out. So based on what I wanted (generally clean tube roundness with more output signal on tap) I ordered a JJ ECC823. I tried it out at practice last night, and it went great! I was able to easily dial in the gain for some nice clean tube saturation, and I had PLENTY of signal with the level at 3 o'clock for the power amp to run without the additional gain stage from the head's preamp.
So I can say this fairly confidently - if you're running a 12AU7 and you like what you have, but need more overall output - try out an ECC823.
And maybe more hypothetically - if you've got a 12AX7 and you like the general breakup you're getting, but you're finding the level knob touchy - try the ECC832/12DW7.
It's a relatively inexpensive experiment - both of these tubes can be found new for less than $25 in the US.