Roly wrote:
WE've got several sets of Christmas tree bulbs and also some other
similar bulbs used for parasol lights etc.

They all have the same type of plastic base and bent wire terminals, but
are of different voltages and wattages.

Some retailers stock some bulbs, but there are some that we can't match.

Is there a dealer who specialises in thses sort of bulbs ? The usual
suspects like RS and CPC don't appear to stock much of this type.

If the original instructions have been lost, is there an easy way to
determine the correct volt and power rating of a given bulb ?

You should be able to figure it out...

Have a good look at the way the bulbs are wired, they will probably be
wired so that the power goes through each bulb in a big loop. E.g.:

L -------- B ---- B ---- B ---- B ---- B ---- B --+
|
N ------------------------------------------------+

L = Line
B = Bulb
N = Neutral

Some sets basically wire the bulbs in two sets:

L -+------ B ---- B ---- B -----------------------+
\-------------------------- B ---- B ---- B --+
|
N ------------------------------------------------+

Or:

L -+------ B ----------- B ----------- B ---------+
\------------ B ----------- B ------------ B -+
|
N ------------------------------------------------+

There may be a few other versions, but I guess the above options would
account for most.

The mains is (give or take a bob or two) 240v.

You can now work out the voltage of the bulbs by counting the number of
bulbs in a set and dividing 240 by that number. If there are different
wattages available in that voltage then you may have problems - if the
wattages are different the distribution of voltage will not be equal
and you will blow something (hopefully the fuse bulb). Try getting a
range of values and see which one causes all the bulbs to be about as
bright as each other.

All in all, the safest option is always to go for a new set, and if you
do so make sure that you keep a note of the bulb type!

Hopefully very soon we will get LED sets so no need to buy new bulbs
every year.

Of course the set manufacturers don't want this because they make thier
money by this bulb confusion trick. Every couple of years you have to
buy a new set because no mater which set you bought you just can't seem
to get the bulbs any more (and even if you can you end up spending the
same for a couple of years' supply as the original set!).

Bah humbug etc...