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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: What are the differences in the 12A_7 series apart from gain? posted by Frihed89 on January 21, 2007 at 03:20:51:
In the RMA/RTMA/RETMA/EIA naming system, the 1st number indicates the approx. filament voltage, the letter(s) are more or less arbitrary - relating to date of assignment, and the 2nd number indicates the number of elements inside the tube.The 12A_7 types are contemporary in introduction. The filaments are set up so both 12.6 V. and 6.3 V. can be used. There are 7 elements in all of these twin triodes: 2 cathodes, 2 grids, 2 plates, and the center tapped heater.
BTW, the use of the word element, not electrode, is significant. 2 electrodes internally connected count as 1 element. The 1S5 pentode/diode illustrates the point. The 1S5 is a 7 pin mini type. It's directly heated. Let's add up the elements. Filament, control grid, screen grid, and 2 plates. Since the pentode's supressor grid is connected internally to the filament, it doesn't increase the element count.
Eli D.
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Follow Ups
- Re: What are the differences in the 12A_7 series apart from gain? - Eli Duttman 05:23:48 01/21/07 (1)
- Thank you - Frihed89 06:48:48 01/21/07 (0)
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