Continuing work for the same friend with my other recent Atlas installs, I just completed this install for him in a newly acquired Atlas SD7, Minneapolis & St Louis #952. This is one of the easiest locos to add the 73100 board to, as it fits without frame modification, and no milling is required even to provide space for the speaker.
First the video (includes some install photos)
Here is a shot of the stock frame, with stock DC board. I was pleasantly surprised to find that the frame is flat over the trucks, both in front and rear.
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One could use the speaker enclosure available from Shapeways / Keystone Details (by
@Lemosteam ) for the Atlas GP38-2/40, but there is even more space on this frame, as shown, but there is enough space to make an even larger enclosure, for fuller sound, by shortening the panhandle (by 1/8") and adding 3/32" more length.
(Keystone Details Enclosure / DC board)
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(Styrene enclosure / ESU board / Soberton 8x12mm speaker)
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Overall length of enclosure is 1.187", height is 0.1755" and panhandle height is 0.0945" and its length is 0.22". Extending the length also allows less overhand of the decoder over the speaker.
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I could have gone with a 9x16mm speaker, but chose to stay with the 8x12, for the enclosure volume (I think you will agree with the depth of sound in the video).
With the speaker so close to the decoder, chose to place a 1206 warm white SMD LED for the rear light. Used one of the included LEDs for the front.
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The contact pads at the front (to the rear of the capacitor bank) are used for track power, the rear pads really don't make contact. The kapton tape was applied more for my own peace of mind, the frame does not contact the board. Not shown, remember to make sure the motor leads, which make contact under the board, also don't contact the frame; the left lead, in particular, is prone to. I slip a small length of 3/64" shrink tubing (don't heat it), to sheath the lead.
As with other locos for this person, no capacitors, but there is plenty of room in the front (with the high hood).
