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Over the years I have accumulated hundreds of tubes, enough to fill a large red Craftsman toolbox. It was a mess in there.
Recently I decided to sort through the tubes and discard the used, stray and unmarked ones. Many had to be put back in their boxes and that kind of thing.
I came across four different Sovtek 12AX7 variants:
12AX7WA
12AX7WB
12AX7WXT
12AX7LPS
I seem to recall that the A and B were almost identical, except for slight tonal differences preferred by certain guitar amp manufacturers. I think they were intended for guitar amp replacement applications and are not ideal for high end audio apps.
The WXT differs from the other three in that it has three mica spacers, like a GE 5751. I believe it was selected for low noise and had more gain than a "standard" 12AX7.
The LPS is their latest version and is a very high performance variation with a larger grid and low hum and noise. It is said to have a "spiral filament", but I thought all filaments were spirals. Go figure!
Can anyone add to this? I'm mostly interested in the 12AX7WXT as it differs from the others with its triple mica construction.
Thanks!
Follow Ups:
I recently had the pleasure of testing some Sovtek 12AX7LPS's for a friend. They all tested around 1500 MicromHOS (what did you call me?!), which is excellent when compared to the JJ's we tested. The JJ's read 1100, less than the 1250 expected of a new tube. He said the LPS's are very good, with excellent tone.
It's probably the best 12AX7 out there right now. It's actually the same as the 12AX7EH, but you knew that.
I found a lot of Chinese 12AX7's when I cleaned out and reorganized my box. Four full sleeves from ProComm. They have that unusual bracket inside like no other. I know they sound good but Mike Sanders at Quicksilver says they are only good for 500 hours. That's bad. I'll never use them.
When retubing I'll just go with the LPS. I've got bigger fish to fry right now. My Rogue Atlas needs a true 600 volt tube and eats weaklings like twinkies. I might have to go to a 6CA7 to be safe.
" It's actually the same as the 12AX7EH, but you knew that."I don't agree. It is NOT the same tube. Where did you get the idea that it was?
And before you come back and say they look alike - that's immaterial. Here's a short list of tubes that look EXACTLY alike:
RCA - 12AX7A and 12AU7A (tubes of the same production era)
RFT - 12AX7, 12AT7, & 12AU7
There are many more, but the point is the appearance of the internal structure is not a conclusive piece of evidence.
In this case, you are way off, since the EH and the LPS have ENTIRELY different plate structures, differences that are readily apparent even to an untrained observer.
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