Identifying manufacturing date (roughly) of some older kit

1) the serial number here will tell you not a lot - s/n records for this period are basically no more or at best incomplete.  If it has been back to the factory in recent years, then there may be a record of any recent service work against the serial number.  However, the "Phono" in place of "Gram" on the NAC12 input means it's likely a later NAC12, built between 1977 and 1980.

2) the serial number indicates a 1982 build date, so likely that this may well be an extruded case NAC32, upgraded to a NAC32.5.  Does it still have RCAs on the phono inputs?  It may well have had them upgraded to BNCs at the time of the 32.5 upgrade.  What are the knobs?  Are they smooth or with slightly ridged edges? I'd need photos of the back, front, inside and out to get a better idea here as there are subtle clues to help date.  All bar the last of the NAC32.5s had red LEDs, although some have been changed to green over the years to match other kit.

3) Impossible to say for sure from the early s/n (see 1 above).  If there's no internal pre-amp supply then it could well indicate it's an early one (pre '74).  But the bolt-down NAP160 ran until 1980 when Naim moved to the current Southampton Road site.

4) See above. the bolt-down NAP250 ran from 1975 until 1980, although some earlier NAP200s were upgraded to NAP250s.

Thank you for the reply Richard.

On the NAC12, if it had 'gram' would this date it at 1974-1977 then? (I have another on the way with gram and without BNCs or phono connectors, just DINs).

On the 32, it's actually marked as 32 but it has the five-pin output and a new 'sticker' has been put on the back to show this.  But the serial number plate wasn't upgraded. 
The knobs are smooth but have a very slight 'pip' where the white line meets the circumference (but this is very slight). 
It's fitted with:
- Two pairs of NA324 issue three cards, 
- One pair of NA321 issue 1 cards,
- One pair of NA322 issue 1 cards,
- One pair of NA 328 issue 1 cards (these have a darker green PCB than the other cards, but I suspect they are not original since they are connected to the input that has phono plugs (rather than BNCs)
- A single  NA 325 issue 1. 

The volume pot is a black ALPS marked 5271 20KX2. 
I've put some pictures here:  https://photos.app.goo.gl/nspYgTMrGn94enJUA 

The 160 has a pre-amp power supply.  So I guess it's simply 1974 'up to' 1980.  I may have a look at the caps in it to see if they have date codes... if I can stop listening to it!

Again, thank you.

Stephen, thanks for posting the photos.  A suspected, yours is indeed an extruded NAC32 later upgrade to a NAC32.5.  The metalised serial number sticker plate shows that it was originally a NAC32, serial number 0932 - so 1982 build. The red LED and smooth edged knobs are all original and correct for this year.  The upgrade saw the fitment of the DIN5 socket for the Hicap, the new rear label showing inputs and pin layout, and also a pair of BNCs replacing the original RCA Phonos on Phono 1 (some had both sets replaced).  The cards are interesting though as they're pretty old.  They are the original "artwork" types and I'd expect to see them on an early unit - say a bolt down NAC32 or NAC12, but not so much on an extruded NAC32.  I have seen some early extruded NAC32s with artwork PCBs though, so I guess yours is probably original. But I don't know the exact dates of when the board series were introduced so can't be sure here. The original artwork main PCB would have been replaced with the upgrade (hence why it's the later style).  Only thing I would definitely want to do though would be to update the Phono boards to at least NA322/3, better NA322/4s. The NA328s are totally obsolete now.  Best replaced by NA326 line link boards, or another set of phono boards if you want another phono input, say for MC carts.

As for early NAC12s, most of them would have been upgraded and updated, probably by Julian on his kitchen table. It makes it hard to pin down exact dates.  My own "Gram" NAC12 started out as a very early one (no extrusions, just alloy panels all screwed together) and was then updated on a few occasions, culminating in a daughter board PCB, replacement of the knife edge connector on the phono board slot to enable fitment of later boards, RCA phonos on the back in place of the phono DIN socket, and an ALPS blue volume pot.

You really ought to write a book, Richard. ????

I wish I'd kept my 32-5. And Nait 2 (olive); although at least I know where my Nait lives and it's still in daily use. ????

Richard, thank you for the information.