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Re: ECC99...

Posted by Lew (A) on July 17, 2002 at 05:57:13

In Reply to: ECC99... posted by Luis on July 16, 2002 at 14:23:48:

Not to mislead Bashir, the ECC99 IS a direct replacement for the 12AU7 or the 12AT7 only in the sense that the pins are wired identically to those of the "12A" series. However, electrically the ECC99 is very different from either tube, as you noted by remarking that resistors must be changed. The ECC99 is closest to the 12AU7 but has higher transconductance and lower plate resistance, resulting in a very slightly higher mu value. It will run best on at least twice the current normally alloted to a 12AU7. In contrast, the ECC99 is way different from a 12AT7 in terms of mu (22 vs 70), so if you substitute the former for the latter, be prepared to deal with a lower gain factor (but this is no worse a penalty than one experiences when going from the Mark I to the Mark II input stages). You would not want to use the ECC99 to replace 12AT7s in the pre-amp phono stages, however.

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