12BZ7 ///12AX7

Jadis always *Please relate all concerns to our USA representative dealer*.
Bluebird, i believe, which is a dead end as for *~~cap I swap tubes,,,~~~
~~what we suggest,,,,,,~~ no doubt will be the answer..
As Blue and Jadis do not want to give the green light and if a curcuit blows, , can’t take the risk for blame..
Seems to me is the system is working with the E80’s, and no shorting/crackles, whistles, pops, then just let it play.
The Defy with AU’s does not offer the fq resolution, forward sound stage, that i require ina amp,.
= I am willing to risk possible issues.
EU E80CC = 12bh7, at least from looking at the 2 designs.
I just boughta bunch of bh’s along witha bunch of bz’s.
The bh’s i will try in the AU section and the bz’s in the Defy’s AX section, will post later this week how these 2 tube rolls went off.
maybe evena YT vid with the new bz’s and bh’s.

OK so the
12bh7 = EU E99CC.

~~Ck with your amp manufacturer~~~
(a bit late for the roll to the E80CC)
https://www.tubesforamps.com/products/12bh7

Just looked at the Defy 7 schematic, audio section. It looks like the 12bz7 would work ok for the audio circuit voltage settings. BUT there is a danger it will draw too much heater current from the filament winding, along with the E80CC, which also draws double the heater current of the original 12au7. I don’t have the power supply section schematic here.
The gain of a 12bh7 is 16.5, the E80CC gain is 27, the ECC99 has a gain of 22. The 12au7 has a gain of 20. Since the 12au7 gain and transconductance sets the voltage for the rest of the input stage on the Defy 7 I’d have a tech familiar with tube circuits to check the voltages and currents over with these alternative tubes you’re trying. There might be a risk of frying the heater winding with too much heater current from these bigger tubes.

I am willing to risk possible issues

OK, It’s your gear, but if your Defy 7 stops working don’t complain about Jadis if they won’t fix it.

I'm not sure how the extra current capability of the 12bz7 over 12ax7 would be an advantage? Most designers place 12ax7 for their gain, not current. They're never reasonably going to be asked to drive a hard load, so you're perhaps not gaining anything meaningful. However the 12au7 is often used as a driver or follower, and I've always heard improvements by subbing in the much stouter 12bh7.

Yes, you have to be careful that you have enough overhead for the extra heater current draw. Always consider the component. For a preamp with 6x 12au7, yeah you're probably in trouble subbing 12bh7's and doubling the heater requirements. For my Rogue Apollos with 4x 12au7 and 12x KT120 - well more than 90% of the heater current is sucked down by the power tubes and an extra 0.3A per 12bh7 didn't pose a problem. And yes it sounded a lot better too!