The Fet Valve amplifiers since the hc versions have used two 12AT7/ECC81 tubes. Earlier versions used two 12AX7 tubes. Circuit changes are necessary to replace the 12AX7 with 12AT7 tubes in older models. Tube life in general is at least two years. There are no necessary adjustments in replacing tubes if the same kind of tubes are used. We supply JJ Electronic (Tesla) ECC81 tubes with current production and have been for over a year now. We have had very good luck with reliability, low noise, high gain, and good sound. Of course a random tube may fail much sooner, but that is the luck of the draw. There is no industry warranty on vacuum tubes at all.
A pair of new tubes is just $29 from us plus our normal minimum order shipping charge of $9.00.
Frank Van Alstine
