12BZ7 ///12AX7

Interesting...
https://www.audioasylum.com/messages/tubes/25401/12au7-vs-e80cc

@ Mulveling, Its about time someone tells 
It eaxtaly as needs be siad
*basic AU suck* including the Holy graisl,,,note even Siemens/Teles AU's can be had pretty cheap.
Its the AX's which go for GOLD.
Yes there are at least 2 or 3 other tubes can be ub for the AU;'s.


@ 
noromance
Great find, well done my friend, backs up some of my findings on the E80CC.
I have to disagree in part,, yet agree in other ideas made from this 2000 post on Audioasylum

*The E80CC projects a  very odd sound stage,,,~~~indeed it does~~~which gives a  MUCH LARGER THAN LIFE SOUNDSTAGE~~~ Indeed. 
My defy was dead, and could not sing due to the Class D chinese clone jadis  preamp,,,with the employment of the E80CC, the jadis came to life, though still at Class B/C fq resolution..Still, thats better than the Class C/D fq resolution with the AU's employed.
~~~~VERY VERY HIFI SOUNDING~~~ The E80CC is High Fidelighy. 
The AU is Low Fidelity = Class C tube. The E80CC is a a Class A design. 
The author goes on to say
~~~ we need futher testing to make a  complete testing vs the AU..~~~
lastly he suggests that his questioner, just avoid the E80CC and stick with 
~~The old tried and true~~
AU.
Based on my testing, the E80CC is The King of all AU's, while all others/Siemens/Teles are mere rogues in comparison.
Now i am on to  discovering the 
~~King of all AX's~~~
which i do believe have found in the 
,,well the Valve Museum does not list a  
12bz7
does list its cousin
The 12BH7A
The build of this 12BZ7 looks identical to the AX design, except a  taller version...

http://www.r-type.org/exhib/aaa1764.htm

The 12bz7's go cheap on ebay,,now after my testing and following up witha  YT vid, that market price might jump.

Note how mucha  single Philips mini watt E80 got today on ebay,,~~$150~~!!!
lsiting says, pinch waist/D ring,,= pure snakeoil.

A E80CC is a  E80CC is a E80CC. The Siemens did, if memory serves me, makea  miniscule pop in fq resolution,,,yet i need to  makea  further testing vs the Philips E80, maybe tomorrow. 
The author in the above Audioasylum mentioned the Philips was superior to Tungstrum,,,which i might also believe is true. But as i say, the pop is so miniscule, its reallya  matter of what you are willing to pay.
A system which lacks the sensitivity to pick up the added fq resolution  of the Siemens, may do equally as well just to grab any E80CC.
As I say, in order fora  Class A tube to operate in 
~~~pure class A~~~ resolution,  the system has to possess ~~Class A sensitivity~~.
My preamp is Class D, The Cayin Class A/B The Thors Class A/B , thus the Lite LS9 pre(Class D) drags the entire Class A/B system down to class B/C. 
Yet in spite of this drag on the resolution, the Defy with its Class A build, does quite well at registering the incredible life offered by the sublime E80CC. 
I've got my work cut out over the next 6 months, and slowly but surely hope to acheieve Class A/B resolution by mid summer. 
In 2021 I hope to achieve 
Pure Class A Resolution of fq's. 

mozartfan, The E80CC is a European designation for a tube. The European designation for the 12AU7 is E82CC and for the 12AT7 it’s E81CC, for example. I don’t know if there is an American designation for the E80CC.

Different tubes have different electrical characteristics. You need to check with the maker of your Defy 7 to make sure that the E80CC’s electrical characteristics won’t damage it over time. It’s really not a good idea to substitute different tube types without finding out if they’re compatible with the equipment.

I checked at Brent Jessee Tubes and it appears that the E80CC is considered a substitute for the E82CC with the caveat that you check with the manufacturer about suitability:

E80CC / 6085:This unusual European tube is basically an industrial type 6085. However, it’s specs are similar enough to a 12AU7 that audiophiles are grabbing them up while the prices are still reasonable. The heater life is rated at 10,000 hours, and some have gold pins. The larger box plate structure gives this tube low microphonics and silky smooth sonics. Since this tube has a much higher Gm and Mu factor than a 12AU7, the gain is going to be greater and this tube will give a more forward presentation. Awesome in phase splitter applications. If in doubt, check with your amp or preamp manufacturer to see if this tube will work OK in your application.

The 12bz7 is basically a double 12ax7, ie. Each 12bz7 triode is similar to two 12ax7 triodes in parallel. It draws double the heater current of a 12ax7 (600mA vs 300mA) and has twice the transconductance. It has a gain of 100, like the 12ax7. Not sure if your Defy 7 can take it, you might need to ask Jadis for help with that. If the circuit was designed for 12ax7s, dropping in a 12bz7 might cause the circuit not to work properly.
In the same way a 12bh7 is similar to a double 12au7 and also draws twice the heater current, and a gain of 20.
I used to use 12bz7s in my tube phono pre of the 90s.

+1 ndevamp.
Check with the manufacturer.