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12BZ7 ///12AX7

Could not finda  topic for tubes, so am using amps section.
After making the amazing discovery of the E80CC as sub for AU~~E80CC blows away every/all AU's, including the *Holy Grails/Siemens,Tele's*.
http://www.r-type.org/exhib/aaa0426.htm
at least in my Defy7, the swap was more than just significant, the Defy came to life from the grave.
I found the Siemens to bea  miniscle superior to Philips = both are equal IMHO, and the valvo Red label E80's going for $$$$$$$$$$ is a scam. Don't buy into it. 
Right now that tube  is going for $50/each. When word gets out  ~~Super Tube~~~the price will rocket, as that tube is not being produced any longer. 
I've loaded up on the Philips label.

so i figured,, maybe there is a  
~~Super Tube~~ for the AX..
After days/weeks of research,,i found this
12BZ7
https://www.radiomuseum.org/tubes/tube_12bz7.html


*Big Boys*
So  ordered a  bunch off ebay, and will arrive next week
Will post a  review.
can not find much on the INET about the 12BZ7,, anyone have experience with this tube?
mozartfan
ndevamp
55 posts
 
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.
tomcy6's avatar
tomcy6
2,587 posts
 
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.
mulveling's avatar
mulveling
1,894 posts
 
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!
lowrider57's avatar
lowrider57
5,417 posts
 
@mozartfan,
I'm not understanding your opinion that the 12AU7/ECC82 sucks. In the Asylum shootout the clear winner was the Brimar Gold Aero Platinum grade 12AU7A.

There are superior drop in substitutes such as the 5814, 5814A, CV4003 Mullard & Brimar, 7316 & 7308 Amperex/Philips. All are in the AU7 family, all low-noise tubes. Many preamps and amps do not recommend using higher current tubes.

ndevamp
55 posts
 
7308 is a 6dj8 equivalent, not 12au7.
The Defy 7 has the 12au7 as input tube, the 12ax7 is the driver tube. The extra current capability of a 12bh7 is unused in this circuit. Same for a 12bz7 in place of the 12ax7 at the same operating current. The miller capacitance is higher in the 12bz7 so the high frequency response will be more restricted. Without modifying the circuit, the performance overall should be worse.

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