Quote:
Originally Posted by mastermanx2001
there appears to be comment on the internet that the 7581A/KT66 has a heater current of 0.9A and the GEC KT66 a heater current of 1.3 A
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I think you're right. Tung-Sol and GE say the 7581 is one of the 6L6 famly with a 0.9A heater see
http://www.pentodepress.com/tubes/7581.pdf or
http://www.pentodepress.com/tubes/7581A.pdf It also has a lower anode current at the standard test point (250V on the anode and screen, -15V on the control grid). You get 85mA from a GEC KT66 at this point but only about 70mA from the 6L6 family. So although it will work OK it won't be quite the same as "the real thing". Actually the reduced heater current only saves you about 5W of transformer load out of a total of more than 80W (10W in the GZ32 heater, 20W plus between the KT66s and EF86s and 50W plus in the HT supply). However if replacing the valves also cuts the HT current you will save a bit more. If you get a chance to make some DC current measurements with the 7581s vs the KT66s in your Quad IIs I'd be interested to see the results. Just measuring the voltage across the cathode resistor would be a good start.
Cheers,
GJ