A protein complex that is located in the endoplasmic reticulum (ER) and is formed by the association of an immunoglobulin heavy chain with the proteins of the ER chaperone complex; the latter include BiP, GRP94; CaBP1, protein disulfide isomerase (PDI), ERdj3, cyclophilin B, ERp72, GRP170, UDP-glucosyltransferase, and SDF2-L1.