Dave, Bud, et. al. This is the one I have. http://www.ebay.com/itm/Tektronix-type-491-Spectrum-Analyzer/251520521790?_trksid=p2050601.c100085.m2372&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140211132617%26meid%3D6730189179249727511%26pid%3D100085%26prg%3D20140211132617%26rk%3D3%26rkt%3D4%26sd%3D390831651675%26clkid%3D6730241812728755910&_qi=RTM1562571 Tony