I think that fireproof card will stay in there. A long half-swastika one
along the front edge of the front PA H/S across the amp and to rear of the
ps H/S and a smaller L-shaped one along the rear of the rear PA H/S. That
one removing the free path run straight to the fan, ie forcing air through
the h/s vanes.
The other one stopping short of the inlet grill to allow some unobstructed
cool air along the long run over the PREA and the ps to the fan

Todays results, adjusted down for an ambient today of 22 deg C, and starting
with similar 7.5 V ac over 4 ohm
5min , PA temp 64, PS temp 26 , exhaust 25 deg C
13 min, 74, 37, 35
fan running noticeably faster by now
20m, 74, 40, 37
30m , 74, 42,37
40m , 74, 44, 38
50m , 74, 45, 38
considering the stem of the ps hs thermometer I had to make a hole in the
card and the end of the stem was then in hotter air than the bulb end temp
maybe. The interboard connectors etc were noticeably not so hot. Makes
thermal runaway to destruction of the SMPS less likely if the amp is driven
excessively hard, hopefully. As far as I can tell with these amps , thermal
monitoring is only on the PA heatsink , not the ps one

yesterdays figures
15 m , 72, 45, 33 deg C
23m, 72, 47, 36
30m , 69,50,36
40m,77,52,37
50m,76,53,37
55m , 75,53,37