A detailed examination of FON 777B, unusual specifications, and the unanswered questions surrounding this remarkable instrument.
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In this article, I would like to share my investigation into a vintage Gibson L-5.
Because of my profession, I have had the opportunity to inspect, repair, and disassemble countless guitars over the years. However, this particular L-5 has proven unlike any other instrument I have encountered. The more I examine it, the more questions it raises. It may well be a one-of-a-kind guitar.
That said, unusual and difficult-to-explain vintage Gibsons are not unheard of. Perhaps it would be more accurate to describe this instrument as one of the many fascinating Gibson guitars whose history cannot be fully explained by conventional specifications.
When I first acquired it, I simply believed it to be an ordinary 1936 Gibson L-5.
At first glance, it appears to be an unremarkable pre-war Gibson L-5.
Features Consistent with a 1936 Build
FON
Factory Order Number (FON)
The Factory Order Number (FON) stamped on this guitar is 777B-2, which is generally considered to date the instrument to around 1936. The letter suffix following the batch number is widely used to determine the production year of Gibson instruments from this period. (Gibson App)
Based on this evidence, it seems reasonable to conclude that production of this guitar began in 1936.
I have searched extensively for other instruments from the same production batch (777B), but so far I have been able to locate only a single Super 400.
If you own a Gibson bearing the 777B Factory Order Number—regardless of the model—I would be very grateful if you could get in touch with me.
The 777B FON stamp and the handwritten “-2” visible inside the treble-side f-hole.
Headstock
Based on the photographs published on the Pre-War Gibson L-5 website, the headstock binding on later examples appears to be joined neatly at the center.
The guitar featured in this article, however, displays the characteristic headstock binding style typically seen on 1936 examples, as shown in the photograph below.
The distinctive headstock binding joint characteristic of 1936 examples.
The headstock also features the thin script Gibson logo, another hallmark of this period.
The thin script Gibson logo and the delicately inlaid flowerpot headstock inlay, both characteristic of this period.
The headstock shown above is from a 1938 Gibson L-5. The binding is neatly joined at the center, and the Gibson logo has become noticeably bolder than on the 1936 example.
Source https://prewargibsonl-5.com/advanced/
Hardware
The guitar is fitted with the flat “L-5” engraved tailpiece, a style believed to have been used only during the brief period from 1935 to 1937.
The simple engraved flat tailpiece, used for only a brief two- to three-year period.
I removed the tailpiece to check for any additional screw holes that might indicate a previous replacement. I also examined the area under UV light but found no evidence that the tailpiece had ever been replaced.
The screw-hole spacing also differs from that of the later Art Deco-style tailpiece that became the hallmark of subsequent L-5 models.
No additional screw holes are present, suggesting that the tailpiece has never been replaced.
Viewed under UV light. The area beneath the tailpiece appears brighter, possibly because it was protected from light exposure and has retained more of the finish’s original fluorescent response.。
The tuners are consistent with the period and are Grover G98 models, which were commonly used around 1936. I found no evidence indicating that the tuners had been replaced.
One of the original screws on the third-string tuner had broken and was replaced.
Grover G98 tuners, believed to have been used until around 1938.
Body Arching
Both the top and back of this guitar have a shape that differs from the traditional arched profile most people would expect. Instead, they feature a relatively broad, flatter area across the peak of the arch.
This type of arching appears to be less commonly seen on L-5 models from the 1940s onward. I previously had the opportunity to repair a 1943 Gibson L-5, and that instrument had a more natural, continuous arched profile.
(Please refer to the following YouTube video for comparison.)
The top features a broad, flatter peak rather than a traditional rounded arch. Another distinctive characteristic is the so-called “double hump” arching. Viewed from the side, the top appears to have two raised areas—one near the neck joint and another near the tailpiece—creating the appearance of a slight top collapse.
This labor-intensive carving method seems to have been replaced by a more natural single-peak arch around the time parallel bracing became officially adopted.
The back also features the same broad, flatter peak in the arching profile.
Another possible characteristic of this period’s body carving is the presence of a recessed area approximately one inch inside the outer binding, creating a shape where water could potentially collect.
A late 1940s Gibson L-7 (shown later in this article) does not appear to have a recess as pronounced as the one seen on this L-5.
Neck Heel
The neck heel also has a shape characteristic of the 1936 period.
As shown in the photograph, there is no visible finish checking or cracking around the joint between the neck and body. Furthermore, UV light inspection revealed no obvious irregularities, leading me to believe that there is no evidence of a neck replacement.
However, Paul, the operator of the Pre-War Gibson L-5 website, offered a different perspective. He pointed out that if this were a factory re-neck performed during the wartime period, any differences in the finish may have already become indistinguishable after more than 80 years.
This neck heel shape appears to be characteristic of the period up to around 1940. Earlier examples seem to have a narrower profile, while later examples appear to transition to a more semicircular shape.
Headstock Back Finish
The finish on the back of the headstock is another characteristic feature of this period. It consists of a stinger (a black-painted area) combined with a darker sunburst finish.
The stinger can be difficult to distinguish in darker lighting conditions.
Bindings
One of the black layers in the outer body binding is noticeably thicker than the others. Based on comparisons with multiple L-5 examples, this appears to have been the standard style used through approximately 1946. Later examples seem to have transitioned to binding with black layers of equal thickness.
The binding on this example shows the thicker outer black layer. The same construction can also be observed on the pickguard binding.
Image courtesy of eBay. A 1947 Gibson L-5. The black layers in the body binding have been changed to a uniform thickness, and the number of binding layers has increased.
Perhaps due to its transitional nature, the pickguard still retains the earlier binding style. Later examples appear to have adopted black binding layers of equal thickness throughout.
The fingerboard material is rosewood.
By approximately 1964, the fingerboard binding had evolved to the form shown above, with the black layers appearing to be of equal thickness.
Although not definitive, the features described above appear to be characteristic of a 1936-era Gibson L-5.
Points of Concern
Bracing
The top features parallel bracing, a specification that is not normally found on 17-inch Gibson L-5 models from 1936.
At the time, the Advanced models were typically built with X-bracing as the standard configuration. However, other examples with similar exceptions have also been confirmed.
Interior view taken through the endpin hole.
Label
This is not necessarily an unusual feature, but rather a disappointing aspect of this guitar.
There are traces suggesting that a label was once attached inside the body, but the label itself is missing.
It is unclear whether the label was never applied in the first place, was removed at the factory for some reason, was taken off by a previous owner, or simply detached over time. However, if the original label had survived, it may have provided important information that could help reveal the complete history of this instrument.
This is not unique to this particular guitar, but it is certainly a regrettable loss when researching a vintage instrument.
UV light reveals a fluorescent area matching the size of the original label, possibly caused by remaining adhesive residue.
No Adjustable Truss Rod
This is the greatest mystery of this instrument.
However, there are known examples of wartime archtop guitars without adjustable truss rods. Even among pre-war models, some custom-order instruments and Hawaiian models are known to have been made without them.
Therefore, the possibility that this guitar was produced during the wartime period cannot be ruled out, although a special-order instrument from 1936 is also a possibility.
UV light inspection provides no evidence of any filled holes beneath the truss rod cover. In addition, the condition of the finish and the way the binding has aged and shrunk, creating a natural level difference with the surrounding wood, suggest that the headstock overlay has not been replaced.
There is no adjustment cavity beneath the truss rod cover.
The tuner holes also show carefully executed stepped drilling.
For reference, the second hole from the top of the truss rod cover was drilled by our workshop at the customer’s request to investigate the possibility that a hidden cavity might exist underneath. The result showed that there was no cavity—only solid wood.
As a side note, there has been some discussion as to whether the original truss rod design had a fundamental flaw.
Having built many guitars myself, I believe that installing a truss rod in the configuration shown in the patent drawing below would not have produced the expected results. In some ways, it might even have been better not to install one at all.
49mm Truss Rod Cover
This truss rod cover is the first-generation style, which was used until around 1937 and was also found on instruments such as Gibson banjos. The spacing between the mounting screws is 49mm, which differs from the standard L-5 truss rod cover dimensions.
Since this guitar does not have an adjustable truss rod, the cover itself serves no functional purpose. It may have been installed purely for aesthetic reasons.
If it had been added by a previous owner, it seems unlikely that they would have specifically chosen this particular truss rod cover. More likely, they would have installed the more common L-5 style cover with the white border and the standard 52mm screw spacing.
Was this truss rod cover original to the instrument in 1936, or was it a wartime-era replacement part used during assembly?
The screws were replaced by our workshop at the customer’s request. The original flat-head screws are also preserved.
A Steel Non-Adjustable Reinforcement Rod Inside the Neck
If this guitar was produced during the wartime period, when the use of steel was restricted, the presence of a steel reinforcement rod itself would seem somewhat contradictory.
However, if the rod was installed discreetly to avoid detection, the situation would become more understandable. In any case, this remains only a hypothesis.
I would like to describe some of the facts that could be confirmed.
A magnet test was performed to investigate the internal neck structure. The results showed magnetic attraction from the nut area to the 14th fret on the fingerboard side. On the back of the neck, magnetic attraction was detected from the 1st to the 14th fret, but not near the nut area.
Based on the difference in the locations where the magnet was attracted, as well as the difference in the strength of the magnetic response felt by hand, it is possible that some type of steel reinforcement, such as a T-bar cut at an angle near the nut area, may have been installed inside the neck.
If it were possible without risk to the instrument, I would be extremely interested in removing the fingerboard and inspecting the construction directly.
On the back of the neck, magnetic attraction was only detected up to this point. (The fingerboard side is shown in the image below.)
Could this indicate the presence of an angled piece of steel reinforcement extending from this point toward the nut?
As a side note, the difference in tuner post heights also reveals the taper of the headstock.
On the fingerboard side, magnetic attraction extends almost to the nut area.
Based on the pattern of magnetic attraction, the neck may contain a reinforcement piece with unequal lengths on the upper and lower sides, or possibly a T-bar that was cut at an angle before installation.
Source：https://www.banjocraft.com/banjo-neck-reinforcement/
The nut was carefully removed for examination; however, no additional evidence regarding the internal neck construction was found.
The fingerboard appears to be rosewood, although this is not considered a unique feature. Similar fingerboards have been observed on numerous other examples.
The “C” Stamp on the Tip of the Headstock
There is a “C” stamp on the very tip of the headstock. Whether this was applied at the Gibson factory or added later by a previous owner remains unknown.
Some members of online forums have suggested that it could indicate a factory second or a B-grade instrument. However, I have not been able to find any documentation showing that Gibson used a “C” stamp for such instruments. Therefore, although this may simply be wishful thinking, I believe the possibility of it being a factory second is relatively low.
Another suggestion I received from a forum was that the “C” stamp may have been applied when the instrument was converted into a cutaway model. However, this theory also lacks any definitive evidence.
Other possibilities that have been proposed include “Custom,” “Change,” or even someone’s initials.
If anyone owns a Gibson instrument with a similar “C” stamp, I would greatly appreciate hearing from you.
The “C” stamp in question. Traces of white ink appear to be present inside the impression. Identifying the origin, manufacturer, and period of use of this stamp would provide an interesting clue toward understanding this instrument’s history.
No Clear Evidence of a Neck Replacement
I initially considered the possibility that this guitar, originally made in 1936, may have undergone a neck replacement during the wartime period. However, no clear evidence indicating that the neck was replaced has been found.
As Paul from the Pre-War L-5 website pointed out, if this was a factory neck replacement performed during the wartime era, any differences in finish or construction may have already blended in after 80–90 years, making them difficult or impossible to identify today, even under UV light inspection.
However, what is most striking is the lack of any noticeable signs suggesting that the neck has been replaced. There is also no evidence of over-lacquering or refinishing.
The binding and heel cap have both aged and contracted in a similar manner, sitting slightly lower than the surrounding wood. This condition suggests that no recent repair or replacement has been performed in this area.
Aging-related checking and cracking in the clear coat around the neck joint can be observed; however, no signs of touch-up or over-lacquering are evident.
Similarly, even under UV light examination, no evidence of repair work or headstock replacement can be found on the back of the headstock.
Neck Dimensions
The neck on this instrument is relatively narrow, measuring approximately 42mm at the nut and around 52mm at the 12th fret. After reviewing available documentation from around 1936, I was able to confirm that necks with a 43mm nut width did exist during this period. Therefore, a 42mm nut width may not be as unusual as initially expected. Further opinions from other examples would be welcome.
The neck thickness itself is not particularly thin. It has a very typical C-shaped profile, or perhaps more accurately, a slightly sharper C shape.
As a side note, perhaps due to the non-adjustable neck reinforcement, this guitar has a tone and resonance that I personally find exceptionally appealing.
The neck has some degree of hump at the body joint (a common issue unrelated to whether or not an adjustable truss rod is present). The upper frets have been corrected through fingerboard work, but there is no indication that the section of the neck containing the reinforcement rod, up to approximately the 14th fret, has required correction.
Fortunately, the neck remains in excellent condition, with no significant warping or twisting.
The Position of the F-Holes Appears Different from a Typical Advanced L-5
First, it is important to consider that X-bracing and parallel bracing impose different limitations on the placement of the f-holes.
Perhaps for this reason, Advanced L-5 models with X-bracing typically have slightly smaller f-holes positioned closer to the outer edge of the top.
With parallel bracing, there is less concern about the f-holes interfering with the braces, which may have allowed them to be positioned closer together.
After examining multiple examples, I found that this characteristic is not unique to this particular instrument. L-5 models with parallel bracing generally appear to have a narrower spacing between the left and right f-holes.
The f-hole spacing is relatively narrow, a characteristic also observed on the adjacent L-7.
25.5-Inch Scale Length
This instrument has a 25.5-inch scale length. However, it appears that many parallel-braced models produced during the same period also featured this scale length.
Although this specification was officially adopted for the L-5 beginning in 1939, it seems that a considerable number of examples with this scale length were already being produced before that time.
With the 25.5-inch long scale, the edge of the f-hole aligns directly with the bridge position. This alignment makes it easier to achieve accurate intonation when positioning the bridge.
F-Hole Size and Shape
This is one of the more interesting points of this instrument.
At first glance, the f-holes appear to have the same small-size shape commonly seen on models such as the L-50 and ES-125. However, after taking actual measurements and comparing them, I found that the f-holes on this L-5 are slightly larger.
The 1949 L-7 has a different, larger-style f-hole shape, but surprisingly, the length of its f-holes is exactly the same as the smaller-style f-holes on this L-5.
Whether this was due to a Gibson design standard, or simply related to manufacturing factors such as jigs and tooling, remains an interesting question.
What is particularly interesting is the strong resemblance between the f-holes of this L-5 and those found on a 1936 Super 400 (shown below).
With the addition of binding around the f-holes, the shape appears as though it would be nearly identical to the Super 400.
The f-holes of a Super 400 from the same period. Early examples can be seen with pearl inlays on the bridge saddle.
The Super 400 is shown above, with this L-5 below. Aside from the presence of binding, the f-hole shapes appear remarkably similar.
Interestingly, despite being produced more than a decade apart, the 17-inch body widths of the L-7 and L-5 are identical.
A Pearl-Inlaid Bridge Found on Early Super 400 Models
Could this be considered a rare feature? It was certainly an exciting discovery for me.
This was the first time I had ever seen one in person, and I found the subtle pearl inlays on the bridge to be remarkably beautiful.
I cannot confirm whether the bridge is original to this instrument, but given the unusual nature of this L-5, I cannot help but wonder if it might actually be original.
Of course, this remains only a possibility and is purely speculative.
An uncommon pearl-inlaid bridge on an early Super 400.
Taken together, these many unusual features cannot be fully explained by the standard specifications of a typical L-5 from this era.
I have also included photographs of various parts of the instrument. Whether they reveal any additional clues or not, I hope they will be helpful for further study and discussion of this guitar.
End block
Parallel bracing
The carefully crafted side reinforcement bracing, a hallmark of vintage Gibson construction
Reinforcement beneath the f-hole and original pencil markings from the manufacturing process
Consistent binding construction throughout the instrument
The aged weather checking has a character that is impossible to replicate artificially.
The beautiful, high-quality figured maple that is characteristic of the L-5.
Hard Case
Since cases can be replaced or acquired separately long after a guitar leaves the factory, they should not be considered reliable evidence when dating or identifying an instrument. Nevertheless, I would like to introduce the original Geib case that accompanied this guitar.
This model was designated Style #440 by Gibson and was known as the Challenge model by Geib.
The oval GEIB INC. stamp on the back indicates that the case was manufactured in 1937 or later. Furthermore, the black hardware and the absence of the red-line trim suggest that it dates from approximately 1942–1945.
According to collectors, finding a case of this specification in such well-preserved condition is extremely uncommon.
To investigate this guitar as objectively as possible, I have carried out the following examinations:
– Internal inspection using an endoscope
– Finish examination under UV light
– Investigation of the neck’s internal structure using magnets
– Precise measurements of various dimensions
– Discussions and exchange of information with overseas researchers
and other forms of research.
As a result, I have reached the conclusion that it is not possible to definitively identify this instrument as either a “1936 model” or a guitar assembled during the wartime period.
Some overseas researchers have suggested the possibility of a Gibson factory re-neck.
However, there are still many unusual characteristics that cannot be fully explained by this theory alone.
The possibilities currently being considered include:
– A Gibson factory re-neck
– A transitional specification instrument
– A guitar assembled during the wartime period
– A prototype or special-order instrument
At this point, however, there is no conclusive evidence supporting any single theory.
For this reason, the purpose of this article is not to present a final conclusion.
Instead, I would like to share as much information about this L-5 as possible and work together with collectors and researchers around the world to uncover the history behind this unique instrument.
If anyone is familiar with an L-5 with similar specifications, has relevant documentation, or has any thoughts or observations to share, I would greatly appreciate hearing from you.
I would also be grateful to hear from anyone who owns a guitar with the FON 777B, regardless of model.
The mystery of this guitar has only just begun.
Update
Gibson Guitars Without an Adjustable Truss Rod
It is well known that many Gibson guitars built during World War II (1942–1945) were produced without an adjustable truss rod. This is commonly seen on Banner-logo flat-top guitars made by the women of the Kalamazoo Gals, and it is not particularly unusual to find archtop models such as the L-50 or L-30 built in the same way. In fact, I own a wartime L-50 with a non-adjustable neck reinforcement.
But what about Gibson’s higher-end models such as the L-5 and L-7?
To investigate, I searched through as many online photographs as I could find. As a result, I located examples of both 1942 and 1943 L-7s equipped with non-adjustable neck reinforcement instead of the familiar adjustable truss rod.
Finding comparable L-5 examples, however, has proven extremely difficult. Whether because so few wartime L-5s were produced or because so few have been documented, photographs of non-adjustable L-5s remain exceptionally scarce.
The first two photographs above show a 1943 Gibson L-7 currently offered for sale (as of July 30, 2026) by Schoenberg Guitars. It features a rosewood tailpiece and a non-adjustable neck reinforcement.
The next example is a 1942 Gibson L-7 currently listed by Dying Breed Music. It has distinctive fingerboard inlays unlike those normally seen on the L-7, and, like the previous example, it is equipped with a non-adjustable neck reinforcement.
This third guitar is another 1943 L-7 that was listed on a UK auction website. It displays the same unusual fingerboard inlay pattern found on the previous instrument.
The following guitar provides an especially interesting example of Gibson fitting a truss rod cover even though the neck contains no adjustable truss rod. I believe this serves as valuable evidence that the L-5 discussed in this article is not an isolated or unique case.
Collectors occasionally mention similar instruments from the 1930s and 1940s on vintage guitar forums, but locating clear photographic evidence is surprisingly difficult.
The photograph below comes from an article published by Jake Wildwood & Co. As noted in the photo caption, the truss rod cover is merely a dummy cover. When removed, the neck is completely flat underneath, with no adjustment nut or truss rod access cavity present.
Shown here is a 1942 Gibson J-45 I found on Reverb. Like the L-5 discussed in this article, it retains a truss rod cover despite having no truss rod installed.
I intend to continue updating this article whenever I discover additional guitars with the same construction.
