Proper use of Lionel #6-5906 Sound Activation Button with KW Transformer?

[Craftech]

1.  Normal 027 tubular track setup on a small 4 x 8 layout (inner and outer loop), Lionel postwar 2026 engine and 6466W tender, KW transformer

2.  Added a Lionel steam sound car which came with the #6-5906 sound activation button

3.  All center rail track taps from the layout are supposed to route through the sound activation button (which they are) to the variable post (A) or (B).

4.  I had replaced the whistle diode in the KW with a 6A10 diode as per these instructions

https://dfarq.homeip.net/lionel-kw-diode-upgrade/

5.  When the whistle handle was activated only the whistle in the tender blew (not the whistle in the sound car) and the bell in the sound car would come on.  Every time.  The engine sped up (as it is supposed to).  The bell would continue ringing until the sound activation button was pressed for 2 seconds or more, or the whistle handle blown for 2 seconds or so.  Button depressed for two plus seconds resulted in the engine slowing down or stopping because of the center rail drain.

6.  Two of those diodes in a row blew (heated up and fractured with a burnt smell) after a week or so in between them.

7.  Because two 6A10 diodes blew up, I Installed a 40A stud mounted diode instead (yesterday).  1N1186RA  200v  40A

Like this:

http://www.tranz4mr.com/KW_Whistle_Diodes.html

8.  Now both the whistle in the tender and the sound car are activated simultaneously with the KW whistle handle and the bell is activated with the #6-5906 sound activation button.

But after only blowing the whistle a few times during the course of the day, the KW started smoking.

The stud diode anode and cathode are the reverse of that of the 6A10.  I guess that is what the RA at the end of 1N1186RA means (that they are reversed). 

I now have removed the stud diode and don't know which is right.  I would think the cathode should be grounded to the mounting bracket (like the way I had the 6A10). 

Thanks for the help,

John