OT: PC Motherboard with a vacuum tube - test-drb@ccmp.vtda.org

7 Sep 2002

On Sep 7,  0:53, Tony Duell wrote:

...
  I'll bet that in, say, 5 years time you'll
still be able to get 12AT7s
 (what's that? ECC82?) 
Roughly.  My Mullard 1977 Data Book lists as equivalents

	12AT7	ECC81
	12AU7	ECC82
	12AX7	ECC83
	12AZ7	ECC81

but I notice that my 1976 book lists ECC81 as obsolescent!  You can still
get them, though.  That's a long obsolescence period!  There's not much
difference, actually; ECC81/82/83 are the same except for gm, mu, -Vg and
Ia:

		      gm	mu	-Vg	 Ia

	ECC81	    5.5mA/V	60	2V	10mA
	ECC82	    2.2mA/V	17	8.5V	10.5mA
	ECC83	    1.6mA/V	90	2V	 1.25mA

And I found the 12AT7 data elsewhere:

	12AT7	    5.5mA/V	55	2V	10mA

The small difference in mu between 12AT7 and ECC81 might just be the result
of minor differences in measurement techniques or manufacturer quality; I
read something that suggests the ECC81/82/83 were designed as exact
replacements for the 12A?7 series.

All data refer to 250V anode voltage.  Those dual triodes are/were often
underrun at 150-200V, and obviously the gain and currents etc change if you
do that.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York