12AX7/ECC83 to ECC88 tube swap?

The 12AU7 has a mu of 20, and a lot of guys have used them in place of a 12AX7 to get less preamp gain, so the signal stays cleaner. It should be similar to that, but with one of the triodes in it being used as the driver tube, it may not drive the 6V6 to full power. Those more in the know than me should illuminate us on that

 

There is a tube used in old Ampeg amps called a 12DW7 a nine pin dual triad one triad has a mu of 100 the other triad has a mu of 20. It is basically half 12 AX7 and half 12AU7. You might have rewire the socket it is a 50/50 chance on that.

 

I wouldn't. The ECC88/6922 is a different design to the 12AX7. Besides different pinouts, other circuit mod's would be needed.
Someone else here may be able to chime in wrt to what those mod's would be. Would be a good mod (if at all possible) for inverter stage, but not for a preamp stage (IMO).

My amp uses an ECC88 as an inverter, which it is well suited for. But the inverter stage was designed around the ECC88.

If you have no use for them, these old stock ECC88's would sell quickly. Amperex, Brimar, RCA ... all top-shelf items.
Check ebay to get an idea of prices you would get.

 

The ECC88 or 6DJ8 is similar to the ECC82 but with a μ of 33.
The heaters are wired pins 4 & 5, pin 9 becomes the screen as this valve was used as a VHF mixer oscillator and the PCC88 employed in VHF/UHF tuner units for television.
I use them, with great success, in my Hi Fi amplifiers as do Audioromy and many more quality manufacturers.
One of the least expensive dual triodes on the market, there are many suppliers with vast stocks of them. Similar to the Soviet 6n1p, the 6n2p has identical μ as the ECC83 with the heater wiring as ECC88.