Tube monoblock pairs restoration, thoughts.

[Pio1980]

Iirc, the consumer era Mac monoblocks all use half a 12AX7 in the front end, the other half lit but otherwise grounded unused.
If this is the case across the board on all vintage versions from MC30 to MC75, why not consider an option to rewire the sockets of the matched pairs "mirror imaged" to use each half of the tubes as intended, but with the unused half heater unconnected to avoid ruining the emission of that cathode. Then, the tubes may be swapped as they become exhausted. Consider doubling the service life of costly NOS tubes in this location.

 

[Steve O]

Just for the record....at least a couple versions of the MC60 used the other half of the input 12AX7 as a form of voltage regulator. The earliest even used an NE2 as a voltage reference. So your idea would not work as planned for the 60 but should be OK for the other lower power monoblocks.

FWIW and just MHO, I’d be more inclined to parallel the two sections and adjust input circuit values accordingly. OTOH, your idea is easier to implement and requires no adjustment to circuit values.

 

[Pio1980]

Just for the record....at least a couple versions of the MC60 used the other half of the input 12AX7 as a form of voltage regulator. The earliest even used an NE2 as a voltage reference. So your idea would not work as planned for the 60 but should be OK for the other lower power monoblocks.

FWIW and just MHO, I’d be more inclined to parallel the two sections and adjust input circuit values accordingly. OTOH, your idea is easier to implement and requires no adjustment to circuit values.