If I toggle F2 on my NCE cab, I can start and stop a horn blowing in any of my locos, regardless of decoder.  But if I summon F2 via my NCE Mini-Panel, once the horn begins to blow there seems to be no way to stop it.  The decoder model in the loco makes no difference.  Am I missing something obvious or does this simply fall into the category, "one of those things?"

I finally discovered the answer to my own question.  To turn off any function requires leaving a bit blank, not treating it as a toggle.

Hi Bob,

The simplest way to get a fully independent supply is to purchase a
"wall wart" or a "brick" supply with appropriate ratings.  So each
Circuitron will draw 15mA.  Allow another 30mA for your DCC control
board.  So you need 12 Volts at 70x45mA=3.2 Amperes.  So you should
probably get a supply rated for 4 Amperes.  This probably gets you into
the brick category. 

Here is a supply that would do the job:
https://www.digikey.com/product-detail/en/globtek-inc/TR9CE5000LCP-N-R6B/1939-1237-ND/8598040
Globtek TR9CE5000LCP-N(R6B).  It is rated for 5 Amperes and is
compatible with your house voltage and regulation situation.

I think you could save a lot of money on both power supply and the
turnouts by purchasing the MP1 from MTB-Model:
https://www.mtb-model.com/pages/mp1.php?lang=en

These turnout motors are slow motion.  Draw no power when in position
and have a set of protected auxiliary contacts that are ideal for
powering frogs.   I would contact them for a good decoder to drive them
as you and they are both in Europe.

I am using them here in the USA and am very happy with them.

Best,

Ken Harstine