THE National guitar has recently been brought to everybody's attention by Mark Knopfler and that record cover.

When this surge of interest subsides, a few more people than previously will covet one but mostly they will settle back into the realm of afficionados who relish the lack of information and the maze of models, the confused serial numbers and the confusing history of the National Dobro Corporation.

It is easy to sustain a vague interest in, say Fender. You can buy an old Tele, look it up in 'The Fender Book' at your local music shop and from the serial number find out the date and anything else of interest.

Not so with these. You may come across a National or a Dobro, but finding out anything at all about it may be difficult.

Mark Makin is an aficionado — a character from Victorian fiction, the knowledgeable amateur. He has a comfortable living as a graphic designer, he pursues interests in music and Egyptology and he has fine collections of obscure tapes and National guitars, on which he is writing and illustrating a book.

Like the fictional character, he is tall, thin, bearded, sharp-eyed and entertaining on his subject.

In a Forties film, he would have got involved in the plot by accident and happen to have the piece of information that demobilizes the mummy and its curse, on a scroll rolled up in his walking cane.

But instead he shows me his guitars and attempts to make their history comprehensible.

The distinctive feature that sets National guitars apart from the rest of the guitar market is the resonator speaker, an attempt to amplify the guitar which pre-dates pick-ups by less than ten years but which has survived because of its distinctive sound and looks.

The idea, an adaptation of the resonator speakers on Twenties gramophones, was that of John Dopera, one of five Czech immigrant brothers who ran a music shop in Los Angeles.

The first National guitar, the Triplate, so called because it had three resonators, was brought out in 1925. This was a lap steel with a square steel neck designed for the pop of the day, Hawaian music.

It worked like this: the three cones, of a light aluminium alloy called duralumin, were mounted like speakers inside the body of the guitar.

The bridge was one third of a 'T' bar, the ends of which rested on the centre of each cone, thereby projecting the sound out of the front of the guitar.

All guitars made by the National Company until 1928 were triplates with a bewildering and poorly documented number of variations, and they continued making them alongside other lines until 1939.

After the first twenty or so hand-made triplates they adopted four basic styles, differentiated by the complexity of the engraving: Style 1 was plain, Style 2 had a pattern called 'wild roses', Style 3 was 'lily of the valley' and Style 4 was 'chrysanthemums'.

Usually German silver, a nickel, copper and zinc alloy, some were made of bell brass in the thirties, sandblasted, not engraved with airbrushed pictures on the back — like the model 97 (price $97) which had a girl on water skis in yellow, blue and white and the style 35 (price $135) which featured a minstrel with a Robin Hood hat and long necked mandolin in red, green and gold. As you can tell, these were often named after their dollar price.

During the years of triplate production some were made with guitar necks instead of square lap steel necks but these are a rarity now as only around 800 were made.

The styles 3 and 4 are also uncommon, they were always intended as prestige instruments with the style 4 costing nearly $200 at a time when an ordinary guitar would cost around $20. They were advertised by film stars of the day like Ramon Navarro and are supposed to have been sold to virtually every royal house in Europe — including our own.

In 1929 two brothers left to form a new company, Dobro, and brought out a guitar with a wood body and single resonator which differed from the National resonators by having aluminium web transferring the sound to the rim of the resonator from the bridge, whereas National had the bridge directly mounted onto the centre of the resonator.

The wooden sound of these Dobros made them popular with country players although the National remained a standard instrument for fast steel players, blues pickers or Hawaiian players.

Soon National and Dobro started attempting to complete directly with each other. Dobro brought out metal-bodied guitars and National brought out wood and metal guitars with single resonators (centre mounted) as well as continuing with triplates.

Apart from a few wooden prototypes, the first National single resonator guitar was the Duolian. By virtue of its single cone, it was cheaper to produce than the triplate and to further cut production costs they reduced the three-piece body to two pieces.

They were available plated or painted, or 'frosted ducco', an effect produced by hitting the guitar with a spike to shatter the finish.

The up-market version of the Duolian was the Triolian with its body painted in a mahogany wood grain (although it was usually metal) and the Polychrome Triolian was brightly painted often orange or yellow with beach scenes.

The colours used on these guitars are so crass that it is hard to think of them as saleable, let alone upmarket, but they do have better necks than Duolians despite looking as if they were painted by maniacs.

The top of the range National single resonator was the Style 0, the one associated now with Dire Straits. These were nickel plated bell brass, stencilled with sandblasted palm tree patterns. Style 0s from different years had different numbers of palm trees!

One feature distinguishing Dobros from Nationals was the f holes. Shaped traditionally on Nationals like the letter f, they were quartered circles, like gunsights, on Dobros. One other distinctive Dobro feature was called fiddle-edging; an effect caused by an attempt to get round construction problems by crimping the edges of the guitar like a tin can.

When is a Dobro not a Dobro? When it's a Regal. They licensed a Chicago company, Regal, to make some, later all, Dobro bodies and assemble them with parts sent from LA.

Sometimes these guitars were called Dobro and sometimes Regal with of course many line variants; either painted, two popular finishes being 'highlighted gold' and 'wood sunburst' or nickel plated, and either plain or engraved with Spanish dancers, Hawaiian scenes or bunches of grapes.

By 1936 Regal made all Dobros (and some country players prefer Regal Dobros to Dobro Dobros rather like the Tokai/Squier/Fender debates of today's guitarists) but by this time National and Dobro had merged again. At first they shared premises but produced two lines independently, then formed the single National Dobro Corporation in 1933.

From then until 1940, when war conditions forced the factory to close due to the unavailability of metal, was the heyday of National guitars. They were producing 60-80 instruments per day and this is the period causing most problems to collectors. Most models were duplicated in four-string tenor guitars (which were initially pear-shaped, then were given smaller guitar bodies), plectrum guitars (which were long-necked tenors) and sometimes banjos, mandolins and even ukeleles.

There was little method to the production and the serial number system was completely changed, so dating things exactly is difficult, especially as different models were made for marketing houses such as Sears Roebuck. They also sold parts to other companies so that it is possible to get guitars which are part Gibson, part Kay and part National or part Harmony part Dobro, and so on. And on.

Mark Makin is attempting to collect information on any that made their way to this country (mostly via Sears Roebuck and importers Boosey and Hawkes) and attempting to properly catalogue the different models, but odd guitars just keep turning up.

One reason why is the although the factory closed in 1939 some were made after that just by assembling pre-war parts, using pieces of different instruments if necessary.

They also made electric guitars. Mark has one called a Silvo which is an electric lap steel dated as late '30s from the plastic on the front, but using an old Duolian tenor guitar body — another oddity nobody can trace.

He also has one of the first Dobro electric guitars, solid aluminium with a disc at one end and a big tungsten magnet, like the Rickenbacker A22 'frying pan' which many guitar books say is the first electric guitar.

But it is not quite as clear cut as that — National and Dobro also brought out guitars at much the same time.

The three companies were very closely linked as Rickenbacker, who had a car body pressing plant, got into the field of guitar making initially by pressing metal National bodies.

Beauchamp and Simpson, the designers of the pickup on the A22, had been working for National before teaming up with Rickenbacker, and there is a 1929 Dobro with a Simpson made pickup.

After a couple of years, the solid aluminium electric lap steels were superceded by ones made of wood or using old National tenor guitar bodies (like the Silvo) and National Dobro were making a confusing array of these alongside the resonator guitars and even fitting resonator guitars with a pickup on a disc in place of the cone as a custom service.

With the closure of the factory for the war, the National story should end, but like everything else about the National/Dobro saga, it's not as clear-cut as that.

Louis Dopera with two of his old Dobro staff retained the right to the National name and formed a new company, Valeo, in 1941.

The company was immediately put into war work, aircraft construction and shrink wrapping food, so that when they started making guitars after the wars, many of them (called either Valeo or National) were shrink wrapped either in plain bright colours or in the mock mother-of-pearl plastic which you only see nowadays on accordions.

These guitars were starting to look like what we would recognise as electric guitars, with the Supro (Ry Cooder plays one) which was made in the Fifties becoming the American Futurama or Watkins, the guitar everybody started on.

One oddity (which Billy Bragg plays) from the late Forties is the Resophonic, a solid body, shrink wrapped resonator guitar without a pickup. It looked electric but actually relied on the resonator for sound and naturally was only made for about a year.

They also made a fibreglass 'Map of America' series of guitars, ribbed inside like an aeroplane wing, and duplicated their whole Supro range with the name Airline.

Valeo eventually sold out to Kay in 1960, who in turn sold out to Seeburg, who closed in 1968 leaving the brand name National somewhere on a Japanese shelf. Perhaps it is about due to re-emerge.

The Dobro name also changed hands but wasn't used until 1968 when Mosrite started making Dobros which were of the same type as the pre-war guitars but of a much lower quality. They also made a Gibson 335-ish semi-acoustic with a resonator.

In 1963 two Dopera brothers started making guitars again, which they called Hound Dogs having no right to the Dobro name. Until, that is, they bought it back in 1970 and formed the Original Musical Instrument Co — who still make chrome plated resonator guitars today and supply parts for models like the triplate, although they've been out of production for over forty years.

Two other companies made resonator guitars in small quantities; Buescher in France made about 400 (ten of which Mark found recently) and Del Vecchio in Brazil made some, one of which Chet Atkins plays.

One twin-resonator National violin was made, and in 1958 three Doperos built a resonator stand-up bass called a Zorko.

Now where can I get a Zorko?