Mystery problem solved within model "A" Ampico Amplifier box!  (The
small box that switches from Medium to Brilliant.)

For some time, I have had difficulty with the amplifier valve not
seating properly when set to brilliant.  The problem was intermittent.
I had replaced the pouch, sealed it, checked and cleaned the bleed,
replaced the gasket, valve leather, and had the correct valve travel.
Usually it worked, but not always.

I have had it disassembled numerous times and have done everything, to
get the valve to seat properly; still, intermittent problems persisted.

I recently discovered that this particular amplifier valve stem is
glued into the wood of the valve button.  This rigidity made the
seating of the valve unpredictable If the valve should seat a bit off
center and not seat squarely, it causes leakage and the dynamic range
of brilliant is lost.

To remedy this, I cut off the valve stem, and glued the stem to a
very small felt dot and glued the felt dot to the center of the valve
leather.  This gives the valve and stem a bit of wobble and allows the
valve stem and valve to have a bit of flexibility and seat correctly on
the leather covered metal top valve seat every time.

(Note that the addition of felt can extend the length of the valve
stem, and there is a possibility of the valve riding the pouch, and
the valve stem may need to be reduced in length,  but in this case
there was plenty of room, and I did not have to alter the length of
the valve stem.)

Another way to do it would be to remove the valve stem, sand the bottom
of the wooden button smooth,  and attach a new bottom valve leather
with a small nail, similar to unit valve stems.

Bruce Clark