I think you mean 12LP4 CRT. I'm thinking it's a 1949 model 4H18 or 4H19.
That uses a 20b1 chassis. Service info courtesy of the ETF here:
Sams 77-1:
http://www.earlytelevision.org/pdf/A...A1_Sams_77.pdf
Riders TV Vol4:
http://www.earlytelevision.org/pdf/a..._rider_tv4.pdf
Admiral service supplement:
http://www.earlytelevision.org/pdf/a...n_sup_20a1.pdf
