My performance impressions—tried 'em in two 1962-era tube receivers
Are you struggling with the question "for a vintage home stereo preamp or amp, are these worth the extra cost?" I was, so I finally bought four to trial. I dropped these into the phono & driver stages of two vintage receivers: 1) a Harman-Kardon TA5000X (same as the HK A500 integrated amp) & 2) a Kenwood KW-60. Sound is SUPERB and exactly as rated in thetubestore's comparison guide: strong and punchy, flat across the sound spectrum, dead quiet, precise at the lowest phono input levels, and nearly zero microphonics even in the phono stage (I tapped each gently with a screwdriver with barely detectable speaker output sound). They replaced original Sylvania/GE 12AX7's and Electro-Harmonix EH-12AX7's and sound similar to the GE's and better to me in gain and clean-solid bass end vs. the EH-12AX7's. YMMV, enjoy the ride, whatever you're listening to!