N Cook wrote:
Because of neighbours and respect for my own hearing I can only check out
combo amps, after repair, in the thermal and electrical power sense with a
dummy load.
Any thoughts on making a vibrational platform driven in range 1/5 to 5 Hz
range say via fractional HP AC or DC motor or large solenoid?
Or are mechanical component failures due more to hours and hours of various
vibration rather than excessive but short duration resonant vibrations, so
it would be a waste of time.

Do what musicians do.

Bounce it up a flight of cellar stairs then roll it across some block
paving on a dolly with rigid wheels, then hurl it into the back of a
Transit van. Be sure to pack it so that it`s regularly bumping against
some other item of gear, then drive it at least a couple of hundred
miles - be sure to get in some inner city potholed roads.
After carelessly unloading the van in the rain, roll the amp across some
cobbles before dragging it up three flights of the fire escape making
sure to clip a door frame or two as you enter the venue, finally balance
said amp precariously on a couple of wobbly beer crates.

you`ll naturally have to miss out the next stage out of respect for your
hearing, but normally the amp is subjected to a prolonged thrashing at
volume 11 for a good two hours with an old bar towel over any
ventilation slots - you should be sure that plenty of clipping and
distortion occurs for this to be a proper scientific test. It`s also
best if the amp is connected to a dodgy power source via a pound shop
four way extension socket. To avoid any unexpected quiet moments,
replace the fuse with silver paper from fag packet.

Repeat the above in reverse order (apart from the actual playing of
course) making sure that the amp doesn`t have time to cool down before
being left outside in the rain for a while before it`s bumpy journey
home and subsequent deposit back in the damp cellar.

Repeat three to four times a week and if the amp can withstand that,
it`ll survive anything you can throw at it in your workshop.

Hope this helps

Ron(UK)