JJ/Tesla ECC832/12DW7 (what is this?)

[scoots]

this jj/tesla preamp tube is listed at the tube depot as half 12ax7 and half 12au7. how does this work? anyone try one of these? results? wwhhaatttt????crazy talk people.

[tazzboy]

I've used that tube. It suppose to smooth out your distortion some.

[Billm]

It depends on where you use it. 12AX7 half is a high-gain preamp. The 12AU7 half has only 20 percent of the gain, but can supply much more current--it's really a driver, but can be used in preamp applications. Ampeg used this tube as a driver for some of its more powerful amps.

Hot Rod Deluxe owners who find the Drive channel a bit much love this tube in V2--it decreases the crunch to more reasonable levels when you kick in Drive/More Drive.

The tube is a complete waste in V2 in Blues Juniors or Blues Deluxes because that stage of the tube is dormant--not used--so the amp just sees the 12AX7 half.

If you put the tube into V1, it does delay the onset of distortion and the maximum amount of distortion available, but it does not increase clean headroom. The loudest clean tone is the same either way--that's determined by the circuit, not the tube.

If you use a 12DW7 in a long-tailed phase inverter, it drives the output tubes unequally, creating distortion. Harp players often do this so they get breakup tone at loudness levels below the feedback point.

The 12DW7 is also a good choice for cathode follower positions because the 12AU7 half has very low internal impedance and can deliver buckets of current to the next stage.