The test circuit This is, as you might recognize, the no R, no C 845 amplifier already described. Connected directly to the CT of the 1660 primary. Connected thru the choke as shown in the schematic above 6AL5 removed, and replaced by a 100 ohm resistor. The 100 ohm resistor bypassed with a 100uF low ESR capacitor. Harmonics below -110dB not reported.
Numbers are dB. below fundamental.
There are several interesting things to note in this table. It also reduces higher order components moreso than lower order components. The 6AL5 diode bias arrangement actually performs better than a resistor bias network, even in this differential stage. Again, the higher order components are reduced more, particularly at lower levels. This ought to sound better, and in listening tests, indeed it seems to sound better.