Random Eiclone Factoid

a DIY, modified Mullard 5-20 monoblock design

Random Eiclone Factoid

Postby Shannon Parks » Sat Mar 06, 2004 8:48 am

The Eiclone monoblock board uses half a 12AX7 as the voltage gain stage. Does this mean that you'll end up with a bunch of half used up 12AX7s? Au contraire....

Image

The first 9A diagram is what we would see looking at the bottom of the PCB. Pins 5 through 9 are wired. Pins 1 through 4 are floating. Lucky for us, rotating the tube 180 degrees (or in this case, the tube socket) lets us access the other half. Clipping the pin 5 leg off of the socket and jumpering the old pins 4 & 5 (providing power to the new pin 9, the CT) complete the procedure. Voila!

Shannon
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Postby nineno » Sat Mar 06, 2004 2:38 pm

So all of that is to say that when the voltage gain tube goes bad you can just clip a pin, rotate the tube, and jump a lead on the socket and continue using the same tube, but the other half right?

Is this going to be a major concern? How often will these tubes burn up?

I suspect there's a tube out there somewhere that is in essance half a 12AX7, right? If someone were inclinded to use that they could, but of course replace it when it goes bad since it doesn't have a "second half," rather than employ the modify and rotate method?

Which one of you tube gurus knows which tube(s) would satisfy all of this?

Of course, since the 12AX7 is soooooo common, any other tube would probably be more expensive. However, for anyone that didn't want to leave half a tube un-used during opperation (and going for some uniqueness points on their DIY build) this might be worth-while...?

All very interesting.....but(!)...When will be be able to buy an EiClone board? After all, i need to have a working amp built before i become too concerned with wearing tubes out, right? :D

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9A Rotate Trick

Postby Shannon Parks » Sat Mar 06, 2004 2:50 pm

drew*,

The whole idea is more about swapping the 12AX7s between amps every six months or so. Using only half a tube might drive some folks crazy and I meant this to help alleviate their suffering. ::D

Shannon

PS Eiclone docs coming. Finally. Honestly.
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Postby nineno » Sat Mar 06, 2004 3:00 pm

Ahhhhh, so this is the vacuum tube equivalent of rotating tires?

Interesting.

I might continue to look into the half-12AX7 tube though, just for fun.

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Postby erichayes » Sat Mar 06, 2004 3:42 pm

Hi All,

The original RCA 12AX7, developed in 1946~47, was spun off as a single triode/dual diode known as a 6AV6. Because the 6AV6 was never adopted by the hi-fi community, its design remained faithful to the original for as long as it was made. The 12AX7, on the other hand, has spawned many mutant variants that aren't really 12AX7s (some are better, some worse) but call themselves same. Thus, it's possible to roll 12AX7s with much more variable results (and fun) than it would be to roll 6AV6s. I suppose that could be a backburner experiment for someone, though...

Another semi-useless factoid: the highly praised 5751 "substitute" for the 'AX7 is really a pair of lowly 6AT6 triode sections thrown into one jug.
Eric in the Jefferson State
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JASSWAG

Postby EWBrown » Mon Mar 08, 2004 7:00 am

Isn't there a variant of the 9 pin tube socket that actually has 12 (or 13) pins in the same form factor and size? I think these had 10 pins around the base, and two or three in the center. I remember from way back seeing some Nixie tube sockets that fit this description. One would have to be careful with inserting a 9 pin tube, as there is no "gap" for making sure that the tube is oriented and connected properly. But it would make tube turning a lot easier, as it would be reversable.

I'll dig thru the boxes of tube sockets at the next NEARC swap meet in Nashua NH in April, and see if I can find any.

The one "mod" I will try later when my Eiclones are finally completed will be to parallel both 12AX7 halves.

/ed brown

JASSWAG ? Just another semi-scientific wild-a$$ guess.
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