The recommended Plate to plate impedance for the 811A in push pull are: At 600 volts 2.5K and 5k at 750 volts. I have made several amps using 100Th, 805,811A, 810 both PP and SE. For good sound the maximum voltage for the 811A is 600 volts at 70ma each PP less SE., you can use higher voltages with the 572B. But at 600 volts you get over 100 watts more than sufficient.
the most important measurement you can make with Hi mu amps is the internal impedance damping factor as it can easily be 8 ohms to 20 ohms. You need to use suitable speakers or the boom can be very bad. I use JBL 2220, Altec 515 many modern speakers are unsuitable for these tubes even with lots of feedback. I have found the 6BL7 or 6BX7 are the best Cathode follower drivers. 6080's are too micro-phonic.
Phil
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the most important measurement you can make with Hi mu amps is the internal impedance damping factor as it can easily be 8 ohms to 20 ohms. You need to use suitable speakers or the boom can be very bad. I use JBL 2220, Altec 515 many modern speakers are unsuitable for these tubes even with lots of feedback. I have found the 6BL7 or 6BX7 are the best Cathode follower drivers. 6080's are too micro-phonic.
Phil
.
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