Hot Rod Deville- New wattage?

[Chuck H]

Lots of speculation. Doesn't even take into account the effect of global NFB.
In case of doubt I prefer to measure.

Agree. But I don't have the amp on my bench. So...

I ran a simulation. Using the test voltages on the HRD schematic to align an amp model that is similar enough. I don't have a 12au7 model but I split the plate loads on the PI for a 5:1 ratio which I assume would be similar to the different amplification factor. The output dropped considerably so I started bumping input voltage until the wave form started compressing. This was at around 36V peak to peak out of the PI. Not enough to drive the output to full power.

[Helmholtz]

Agree. But I don't have the amp on my bench.

But the OP has.

I split the plate loads on the PI for a 5:1 ratio which I assume would be similar to the different amplification factor.

The amplification factor µ of a triode is a theoretical value which does not linearly translate to actual gain.
LTPI gain ratio between ECC83 and ECC82 should be close to 3.
Nevertheless you might have a valid point here and the resulting off-center biasing of the ECC82/12AU7 will make things even worse.

[pdf64]

The table in this post is good for seeing how other valve types work compared to ECC83 in a standard ECC83 common cathode circuit https://www.thegearpage.net/board/in...table.2279173/

[Helmholtz]

I recommend to read the whole TGP thread linked by pdf64 above.
There's some excellent explanation why a 12AU7 performs poorly in a 12AX7 circuit, especially regarding headroom/early single sided clipping.

[Helmholtz]

Also highly recommended: R.Kuehnel's calculators on ampbooks.
https://www.ampbooks.com/mobile/ampl...g-tailed-pair/

[Chuck H]

Also highly recommended: R.Kuehnel's calculators on ampbooks.
https://www.ampbooks.com/mobile/ampl...g-tailed-pair/

I access that site sometimes and endorse this.