...I was just looking at the manual last night too.
I also searched for the Owners/User Manual and came up with nothing?
It could very well be that its just not available "Free" to download? Hey, it happens but not that its impossible to find just keep searching and asking and I'm sure you'll probably find it but for a small cost?
Back to the lamps/bulb replacement, does that Nikko receiver take lamps that look like fuse lamp types? Or are they the basic wedge type?
Just a suggestion here, but if they are the fuse type, there is a seller on Ebay that sells LED lamps that are an exact fit for fuse lamp types. If you were to install these, when lit up, that Nikkio display would look a hundred times better than just using ordinary lamps, in my opinion. I say this because I have already done this by switching out fuse type lamps on several of my tuners and a couple of other pieces of audio equipment as well. Believe me once you install them and see for yourself you'll be amazed at how different and vibrant the display becomes, it just jumps out at you.
Of course you'll play a bit more but its very well worth it.
The choice is yours!
Good Luck on the receiver and hope you find that Owners/User Manual!
EDIT: First off let me state for the record that I am in no way affiliated with this seller on Ebay, like I previously stated, I just purchase LED lamps from him but these are good quality type. Yes there are others that sell LED's that are similar and at a different price but I am very satisfied and have had good results with these. I have posted a few pictures of the results on my tuners here in AK but you can also check out the examples that he has. This is the seller on Ebay that I purchased mine from:
http://www.ebay.com/itm/LED-fuse-la...pt=Vintage_Electronics_R2&hash=item2c85dfbb17