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Here's a big Martin in good shape. 3v top loader. No major dents. Bell looks straight and the price looks OK. Seller posted pictures from most all angles.

If you are looking for this kind of horn, it could be a real deal.

$1350 Buy it now, $150 for shipping.

http://cgi.ebay.com/MARTIN-MAMMOTH-BBb- ... _500wt_744" target="_blank" target="_blank" target="_blank

Here's another:

Different seller. 3v front loader, $1895 Buy it now. No listed shipping. Also offers "Best Offer" selling.

http://cgi.ebay.com/BBb-Martin-Tuba-Det ... 1265wt_729" target="_blank" target="_blank

I believe the second, front action martin is not the 6/4 sized horn but the smaller horn - somewhere around a 2341 (or even a hair smaller) . Lee Stofer had one of these in his shop a while ago, and it may still be in his avatar picture.