Hi:

You note that the 6BQ5 spec sheet shows 130 ohm cathode resistor for 2
tubes, class AB PP. Be aware that this is for designs at approx max ratings
of 300V A-K: the AA151 runs the 6BQ5s WAY over max plate voltage at
something like 360V A-K (similar to Dyna ST/SCA35). It seems reasonable to
assume that if the original design used 100 ohms for four cathodes,
equivalent for two pairs of two cathodes ea would be 200 ohms and this is
still running the BQ5s pretty hot. I'd be inclined to run more like 220-250
ohm @10W ea.

A real benefit of separating the common K resistor is that a matched quad of
BQ5s is no longer required, just two matched pairs. Heath (and Dyna) don't
really do a good job of alerting the user to this issue. Individual K
resistors reduce the need for matched pairs but if it were my amp, I'd still
go for them.

--
Steve