Figure below shows the internal structure of the ROYAL DEVICE BE50 and BE51 OUTPUT TRANSFORMERS  that can be indifferently used  as AUTOtransformer or TRANSFORMER. The BE 30/50 instruction manual gives all the relevant interconnections for the purpose

Figure below shows the amp dumping towards to the speaker. Graph 1 is under dumped condition, long bass and distortion occur on the medium frequency range. Graph 3 shows an overdumped condition where lack of bass and compressed medium frequency sound ocur. Graph 2 shows the correct dumping. Correct dumping may not be correctly achieved without output transformers.

The yellow box below shows as an example all the choices available for speakers with nominal impedance starting from 3 to 8 ohms. Several possibilities are available. Speaker dumping factor can be chosen. For an 8 ohm speaker the choices are 5 or 6 (the first 6 in the yellow box)

Blu Eyes 30/33 and 50/53 model schematic diagram

The new BE 51 OUTPUT TRANSFORMER gives the possibility to connect onto two separate coils the WOOFER and the HI-RANGE driver/s with the choice to have two different coils for the same OUTPUT  impedance (0 dB difference) or to have it with a slightly different decoulpling (0,6 dB difference). In this way the Energy sent back by the woofer will be more decoupled from the high range drivers. This reduce more the interaction between the drivers due to their electromotive force. The result is a much more clean mid and high range than ever in respect to a simple BI-WIRING connection. It is much more very similar to a BI-AMP connection, without ecountering all the problems for a real BI-AMPing.

Considering also the FULL single ended completely no-feed-back CLASS A circuit with dynamic bias regulation brings to an uptodate unknown outstanding sound.

From experience the +0,6 dB decoupling (normally) on the Tweeter, helps restore also loss of highs on the connection signal path from the source to the  speakers, that even with the best coupling always lack somewhere.

The amp comes with double output on the POSITIVE TERMINAL and needs the new RD-BI_AMP cables.

Notes on output stage

The output stage is a Single Ended configuration made by 2 output transistor devices. (NOT MOSFET that are by themselves internally feedback).

Even if the load seems to be connected to the output device emitters, the output is a  COMMON EMITTER STAGE. This is due to the fact that the input signal is in common with the EMITTER and the BASE of the transistor by means of the INTER-STAGE TRANSFORMER and not fed to the BASE in respect to GROUND as normally done on any PUSH PULL amp.  Moreover ONLY a common Emitter stage can amplify either in voltage and current modes as a S.E. TRIODE OUTPUT does. Emitter follower does supply ONLY current amplification. The Voltage stage amplification here is roughly 10 (as TRIODE S.E. output stages). The LOAD has to be seen to be connected to the COLLECTOR (see equivalent circuit drawing here after). Common Emitter mode can only be biased in CLASS A if used as linear device in Audio systems. The  CLASS A BIAS dynamic regulation is a DECOUPLED FEED FORWARD, not a NEGATIVE FEED BACK. See Royal Device Dynamic class A biasing and measures