> > Almost any dual triode can be made into a flip-flop, so your 8 transistors > can fit into 4 bottles. Even a 7-pin 6J6 can work, since flip-flops > generally have common cathodes anyway. > Yep, it is a digital circuit, bouncing between cutoff, and saturation. That said, there is some method to your choice of triode.
Of all the triodes, the 12AT7 (ECC81), 12AU7 (ECC82) , & 12AX7 (ECC83), are all still being made. They are still used in the audiophile, and guitar amp markets. Their heater power (12.6V*150mA=1.89W), is lower than all the other triodes. That means you can always find replacements, and they don't heat the box as much. BUT, since they still are being used a lot, their prices are a lot higher. ~$10 each, for the lower end ones. Since this is a digital circuit, that's all we need. Of these three, the 12AT7 & 12AU7 were used in logic circuits, because they have lower plate resistance. That means they can switch faster. When all you had were tubes, then the faster ones were the ones you used. In a clock app, switching speed isn't important, but a 12AX7 would need higher resistor values to do the job. This would limit its fanout, and make it more susceptible to interference. The 6J6 (ECC91) is a great little tube. It was also used in logic circuits. Its small, and if you look online, they are cheap. They also have a low plate resistance, comparable to a 12AU7, but with higher amplification factor. Down side is that the heater uses 2.84W. 1.5 times what a 12AU7 or 12AT7 would use. Also, they haven't been made in decades. If you do decide to uses these, get at least twice as many as used in the project. You might not be able to get them later. Also since they do get hotter, make sure you have good ventilation thru your chassis. A fan, or two, might be a good idea. Another cheap tube that gets no respect is the 6BQ7/6BZ7 (6.3V*400mA=2.5W). 33% more heater power than a 12AU7, and specs close to a 6J6. Its a 9-pin tube. It really gets no respect out there, so its real cheap. Sometimes you can find these under a buck. Again buy more than you need, because its no longer made. If you're crammed for space, consider a 6EZ8, its a triple triode, in a 9-pin package. 6.3V at 450mA, so its the same heater power as a 6J6, but that's for 3 triodes as opposed to two. So per triode, its the same as a 12AU7. It specs close to a well used 12AT7 (that's near the end of its life). Also, to make it fit in 9-pins, the cathodes of two triodes, are tied to the heater. The cathodes will all be tied to ground, if you use this one. No bias resistor in the cathode leg. A negative bias supply is needed. Down side: No longer made, and already a bit harder to find than all the other tubes mentioned above. There are other triple triodes, with 9-pin bases, with a shared cathode, but most of those use much higher heater power. There are also, triple triodes in 12-pin "compactron" packages. Prices and availability, make most of these poor choices, unless you're the luck fellow, who stumbled upon a crate of them, and got 'em cheap. Personally, I'm going with thyratron ring counters. Speaking of stumbling upon a crate, I ran across 100 of these: http://www.nj7p.org/Tube4.php?tube=5663 Need 28 for my, so far, only 'pencil whipped' design. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
