OT: PC Motherboard with a vacuum tube

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