I have tube rolled Octave MRE 130's for years, driving B&W N800's. Currently, I have a set eight of SED KT88's in primary use. I also have EH KT88's and Gold Lion KT88's that I swap in and out from time to time. Originally I have TAD tubes that were good but seemed to bite the dust after a few months. You have experienced a bad tube for sure. Good thing that Octave builds in bullet proof protection circuitry to save your components.
The advantage of getting a Black Box or Super Black Box is that you will have more AC capacitance in the transformers, an increase in available AC power to drive your speakers. The difference between an amplifier using a Super Black Box; V70, V80 and MRE 130 is night and day. The bass is more powerful and the system can play louder. Overall, the musical presentation is more defined and it is easier to drive your difficult load speakers.
The dynamic and tonal stability of an amplifier is strongly dependent upon the stability and capacity of the power supply, therefore the Black Box and Super Black Box were developed as external upgrades to the OCTAVE amplifiers power supply storage capacitors by increasing their capacitance by a factor of 4 (Black Box) or 10
(Super Black Box), respectively. This is a tremendous benefit if the speaker is difficult to drive. Loudspeaker efficiency is made less critical, while the amplifier is enabled to handle speakers with minimum impedances as low as 2 Ohms.
The power supply capacitance increase realized via use of the Black Box or Super Black Box stabilizes current delivery and reduces the impedance interaction of the load. This improves dynamic range, separation, depth, soundstage size and articulation, rendering the
musical reproduction clearer throughout the entire frequency range.
The amplifier remains unaffected by mains variations and interferences due to the noise filtering characteristics of the capacitors.
I just upgraded to the Octave Jubilee preamp. What a difference that has been compared to the Octave HP500SE. I am seriously thinking about upgrading to the Octave Jubilee monoamps.
I have been a satisfied Octave customer for years.
Where are you located?