12BZ7 ///12AX7

The BH/BZ/AX data sheets all look similar in the same way that a bicycle is similar to a motorbike. They have the same number of wheels and you need to balance to ride them.
Well if nothing else you’re enthusiastic about it all! But don’t be disappointed if it doesn’t work out. Do yourself a favour and have a tech check the operation.
Gain in the tube also sets the circuit dc voltages, not just the volume control position. If you look at the data sheets you’ll notice the amplification factor and current ratings are totally different for each tube, reflecting the different control grid construction and size of each.

BZ7’s arrived, = No go, 12AX7’s out shot the BZ’s in every area.
Now i am on witness a shoot out twix several AX’s
RCA Tall Black Plates vs
 Philips Miniwatt vs
Shugaung T series vs
Siemens  ,
~~~USA vs
Gerjmany vs
Holland vs
China~~~~~
One of these 4 finalists will be given a ~~~Gold Medal~~Silver Medal~~Bronze Medal~~Copper Medal.
,i have no idea howm this Olympic battle will go down.
All 4 are Legenday and may result in all receiving Gold = Miniscule dif.
also want to try Baldwin Organ AX’s. which i am guessing is a RCA.
IMHO Philips is Amperex SQ , made in the legendary Herleen plant,
Phlips Mini watts = Amperex Bugle Boys.
what it comes down to is this
All NOS (rated at least strong) are near equalin voicing. The more important concern are what caps are employed in the amps design.
Tech guys with testing equipment lay claim that if low price cap A tests near equal to high price cap B, then sonaiclly both with sound very sililiar ina amp.
Yet my concern is the limitations imposed by measurable equipment.
IOW I believe there may be more to a cap’s voicing of music, that can not be meausredn ~~~~completely with NUANCES~~~ by a test screen.
Its kinda of likea botanist studing flowers. A text book along with disections/images, still misses the flower in its own enviornment in full bloom.
someone over at DIY mentioned it is near impossible to determine the sound quality of a unit, based ona compressed YT vid witha low level mic/camcorder.
True and yet not so true.
I have skill at listening to what a unit sunds like in real time. If you can not hear the high fidelity of these M caps, you need a hearing aid.
The M caps glorious sing the muisc.

https://www.youtube.com/watch?v=XfqWgHqiPwQ

Mahlerfan, do you give your tubes time to break in??
It seems like they go in and out of your amp pretty fast.

Try some "used test strong" Telefunken 12ax7 when you get a chance. They’re solid all-rounders, and relatively common on the 2nd hand markets. But favorite 12ax7, by a good margin, has been the Mazda silver/chrome plate. Unfortunately they’re rare and expensive ($350+ a pair), and they have a bit of extra energy up top - so won’t be ideal for systems that need a push towards a relaxed top end.

Also I like those RCA tall black plates pretty well, but think the Mazdas are much better.