Spoons said:
So here are a couple of the tube choices I have seen in this thread...
V1 : JAN PhillipsECG 12AX7WA
V2: Mullard CV4024 (12AT7)
V3: Mullard 12AX7 reissue
V4: Jan PhillipsECG 12AX7WA
V5: ElectroHarmonix 12AX7A
V1 = Raytheon long black plate, halo-getter12AX7
V2 = Mullard CV4024/12AT7WA (654 type, ’70’s-‘80’s production)
V3 = RCA 5751 black plate/3-mica
V4 = Mullard long plate/halo getter ECC83 (f91 and f92 types, late ‘50’s production)
V5 = RCA black plate 12BZ7
Right now it's still all Greek to me, these two examples look VERY different except for V2 which kinda "appears" to be the about same. I couldn't tell what the difference in current draw is based on that information if my life depended on it! How do you know what the current draw of a tube is; moreover, how do you know what your preamp (like a Triaxis) will handle?
I know I'll get throught this but right now I feel like I'm gonna explode with information!! :wink:
Just as in a good Thanksgiving banquet, you've got to learn to pace yourself. Otherwise, you'll
end up like Mr. Creosote.
The terms used to describe tubes, like "black-plate" or "square-getter" are just a way of distinguishing which exact version of a manufacturer's tubes. There is quite a sonic character difference between a long black-plate Sylvania 12AX7, and a long gray-plate Sylvania 12AX7, for instance. "Long" plates are approximately 17mm, whereas "short" are 14mm, by the way. Just ask if you need clarification on the terms.
The second tube set, beginning with a Raytheon black-plate 12AX7A, is from my earliest posting. Since that time, I changed the V1 from the Raytheon to a 1956 short black-plate Sylvania 12AX7, and V2 from a Mullard CV4024 to a '50s black-plate RCA 12AT7. This change allowed me to keep the early-breakup quality I liked from the Raytheon, in Lead 1 modes, since the Sylvania also breaks up early, but get the advantage of fatter low frequencies afforded by the Sylvania (Raytheon has thinner bass) in Lead 1.
The RCA black-plate 12AT7 has the more lively dynamic response that I've come to recognize as associated with earlier black-plate tubes. This 12AT7 is more like other 12AT7 - it is tonally thinner and brighter than the Mullard CV4024 (which is also a 12AT7). The extra fat of the short black-plate Sylvania is offset by this thinner-sounding RCA, to a degree, and I made the V1 and V2 swaps at the same time, so the tubes could compliment each other.
That said, I'd recommend the Raytheon 12AX7A V1 and Mullard CV4024 V2 combination, simply because those tubes are more readily available. The short black-plate Sylvania 12AX7 was only made in 1956, and is difficult to obtain.
Now, to the current draw question:
In comparison to the 12AX7 the circuits were designed for, the 12AT7 and 12BZ7 will draw more current. How much? Here is a useful reference link:
WeberVST Tube Data Page. A 12AX7 heater draws 300 mA; 12AT7 draws 450mA, and 12BZ7 draws 600mA. That is 450mA more than the Triaxis was designed for. But most amp manufacturers over-spec their designs, and Mesa is no slouch in this regard. Can it be a problem? I can only testify that I've been running my Triaxis for years, now, this way - not a problem for me!
Bon appetit! :mrgreen:
- T
