The low resistance cathode resistors in the Dynacos (except the ST- and SCA- 35s) is there just to make bias measurement easier. For some reason, way back in their early days, they chose 1.56 volts as their default "correct bias measurement" voltage, so some amps have 15.6 ohms, some have 12, etc. I just go with 10 ohms, and for the ST-70, set the bias at 1.00 VDC (100 mA through two EL34s). Eliminates the mental math.
I haven't done a trial run of the same amp using fixed bias and then cathode bias, for comparison purposes, so I cannot state which would sound bettter. I would side with fixed bias, but then it does have a little added complexity, as compared to the "self-adjusting" cathode biasing.
Fixed bias will give you a bit more power, just because those 13 to 28 volts DC aren't "wasted" in the cathode resistor. Some fixed-bias amps dispense with the cathode resistor altogether, either by switching it out (shorted) during normal usage, or bias is measured through the plate circuit. (caution: High Voltage!)
Either method, I do like having individual bias adjustment for each tube, as compared to all four together in the ST-35 or in pairs in the ST-70.
Eiclones in progress, will repoort once they are powered up and running.
The gold-plated high end amps like McIntosh do use cathode feedback, in addition to UL taps, as well as some global feedback. The Tamura trannies that were listed in E-bay also have the extra cathode feedback winding.
I have two small (10 watt?) Baldwin organ OPTs that have a cathode FB winding, though no UL taps. The primary impedance is approx 6600 Ohms CT, the cathode winding is approx 77 Ohms impedance, and the single output impedance is 8 ohms. The cathode winding is about 8 ohms DC resistance total, FWIW. I'll eventually figure out a simple 6AQ5 or SV83 amp circuit for these.
/ed brown in NH