Just got done amp rolling my early 299D and early 299C. The 299D has been recapped with sonicaps, mundorf SIO and auricaps. It's tube set, Telefunken 12ax7 smooth plates, strong Westinghouse outputs, and a Mullard 5AR4. The 299C has only sonicaps, Ei 12ax7s, EH outputs and a JAN 5AR4. Both have same iron. The 299C sounds better(go figure..), with more detail and better highs. The 299D has more soundstage and better mids. Both amps are great, but the old goldface 299C gets the edge.