To answer Jerry Bacon's questions, the rewind control on the
Seeburg L, and most Seeburg coin pianos, are lock and cancel.  Once
the Rewind slot signals the rewind pneumatic, the transmission stays
in rewind position until the end of the roll when the cancel slot at
the beginning of the roll signals the Play pneumatic to unlatch the
rewind control (and causes a grinding of gears).

I do not have any information on the date of manufacture, but I'm
sure other readers will have that information.

It is not a good idea to take a reading at the pump box, and I am
surprised that the pump wasn't damaged.  The reading of 70 to 100
inches indicates the pump has some leaks, but that might have saved
the pump from damage when you took a direct reading from it.  With
the small stack in the Seeburg L, even with some leakage in the pump,
there is usually an adequate supply of vacuum, causing visitors to
complain that it is too loud.

The pump is connected to a regulator box, which contains a spill
valve to prevent damage to the pump and adjust the first stage of
loudness.  There is also a soft re-regulator on the regulator box.
When activated by the "Soft" perforation, it causes a choke to
re-route the vacuum and drop the level by about 50%.

The mandolin and hammer rail lift are teed together, making it a bit
softer when the mandolin rail is down.  The soft choke pneumatic drops
the vacuum even lower, therefore giving four levels of loudness:

1. Loud,
2. Soft,
3. Mandolin plus hammer rail lift, and
4. Soft with Mandolin plus hammer rail lift.

When adjusted correctly the expression is quite impressive.

The spill valve specification is 25" for loud and 12" to 14" for soft
when the soft perforation on the roll signals for soft, or when the
"Soft-Loud" knob is set on Soft.

The soft level is regulated by spring tension on the re-regulator.
This regulator also has a screw adjustment to make certain the soft
level does not drop too low during heavy passages of notes.

If you are not able to get the specified readings, this might
indicate valve leakage in the stack.  The problem here is brass valve
seats that react with the leather valves.  Apparently the acid in the
leather corrodes the brass seats, causing the leather valves not to
seal completely.  The solution to this is to remove the wooden valve
tops, remove the valves, clean the brass seats, and lacquer them
before putting the valves back in place.

Bruce Clark