@digistar2012: IMHO "Piya tu" song from Caravan is a mastering wonder, specially the prelude upto RD's 'Monica'.....to me it has same effect of any good mono mastering ever done in west also.... and this effect is brilliantly cut in the vinyl...thanks to the engineer whoever he was. The full record has lots of experimentation, so I think RD and HMV put special attention to it.
As for 'Hum Dono', it's a 45 RPM 12" record having all the positiveness of it, of course the recording & mastering is also of top class.
Comparison to later (80's Lps) is not always justified as technology had a change after HMV opened their new studio in Bombay. Some of the 80's Mono records of RD(i.e. Harjaee, Manzil Manzil, Masoom to name a few) have excellent reproduction quality. It's not clear to me, in case of Hindi film songs, why such a big difference between SQ of various films/records existed. Some were too good, whereas some were crap. May be had something to do with producers interest/fund allocation towards music.
Regards,
Bhaskar