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 Post subject: Re: Gilbert portable.
PostPosted: Sun Aug 20, 2017 3:49 pm 
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Victor II
Joined: Fri Jan 06, 2012 6:22 am
Posts: 257
Hi Carlos, Great to see it arrived safely and fits !


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 3:29 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
I could rehaul the soundbox in the meanwhile. Fortunately disassembling the parts was a very easy and straightforward process, I would say it's a soundbox which is easy to work with.

With my suprise, I've found out that the gaskets are really pressed in position by the mother-of-pearl disc (I thought it was just whistles and bells having no influence on sound). The latter was cemented to the dried gasket below, which was hard as glass, although it came off quite easily. The mother-of-pearl disc is thick and will bear the use of some force, but not too much as it is also fragile, especially at the centre.

What gave me nightmares was the diaphragm below. It was originally layed on a rubber ring, which eventually melted and overlapped its circumference, and later solidified just as the tubing gasket. By chiseling it piece by piece, I could finally disassemble the diaphragm without tearing it. The diaphragm has a white enamel treatment which I beleive is unique to Gilbert and that I absolutely wanted to preserve, also beacause finding a spare part would have been nearly impossible I suppose.

Unfortunately the flat rubber ring is also not available as a spare part as far as I know, so I had to put tubing gaskets both below and in top of the diaphragm. Although I managed to close the soundbox, it resulted in a lot of pressure (too much pressure methinks) on the diaphragm's circumference. The diaphragm itself, although being thin and having some corrugations, is of a very stiff type. Although the soundbox looks spectacular, all in all the sound is thin and with low volume. I'm not happy with it and I would like to experiment with some other more efficient soundbox.

The calibration of the needlebar is quite easy. There is no up-down backlash so the diaphragm has to be centered perfectly by trial-and-error. A limited left-right misalignment can be recovered by slightly bending the bar. The bar-to-diaphragm distance is then adjustable with the screws. I didn't get exactly if the screws are eccentric or if the coils are non-flat, however while turning the screws the bar join moves back and forth and it's quite easy to find the position where it barely touches the diaphragm.

While on the task, I took some pictures that someone may find useful as a reference in the future.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 3:31 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
Finally, the soundbox polished and calibrated.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 5:01 am 
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Victor III
Joined: Sun Mar 15, 2009 6:18 am
Posts: 655
Marco Gilardetti wrote:
Although the soundbox looks spectacular, all in all the sound is thin and with low volume. I'm not happy with it and I would like to experiment with some other more efficient soundbox.



You may want to try a thinner and softer gasket, the high pressure may be preventing the full pumping movement of the thick diaphragm. I never reworked the Gilbert soundboxes I have, but they have a quite loud sound. I thought that the loudness came from the Gilbert arm, but I tried one of the soundboxes in another gramophone and it was also loud.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 6:13 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
Mmmmh... that's exactly the contrary of what I hear. Do you know any reliable source of "thinner and softer gaskets"? Something that you have used personally and would recommend, if possible. Those that I used are the standard ones for the Exhibition, bought in the USA time ago.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 6:38 am 
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Victor III
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Location: near Utopia, UK
Marco, in your final photo the white gasket seems to be squeezing out past the mother-of-pearl disc in some places and not others - doesn't look right to my eyes - or is it a shadow effect in the photograph?

Another thing you could try is to cut very small rubber washers, either from thin rubber sheet or small slivers of the gasket rubber, and place them between the front plate and body when refitting the screws, so that the clamping effect has some hold-off/relief/gap, and adjustment possible.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 7:56 am 
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Victor III
Joined: Sun Mar 15, 2009 6:18 am
Posts: 655
Marco Gilardetti wrote:
Mmmmh... that's exactly the contrary of what I hear. Do you know any reliable source of "thinner and softer gaskets"? Something that you have used personally and would recommend, if possible. Those that I used are the standard ones for the Exhibition, bought in the USA time ago.


Marco, the aluminum diaphragms that work under compression are those with the radial folds that act as springs, like the HMV 5a/5B, the Victor orthophonic. The rim of the diaphragm in these soundboxes is clamped to the frame and the inner part is the one that moves. This Gilbert looks more like the EMG diaphragm, it has a small fold near the center but to me for it to perform well the whole diameter needs to move (it is also quite thick aluminum), therefore if it gets clamped it will not perform well (like a mica diaphragm). I have an old stock tubing that is very pliable, I bought in an auction but I don't really know where it was purchased.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 10:22 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
Orchorsol wrote:
Marco, in your final photo the white gasket seems to be squeezing out past the mother-of-pearl disc in some places and not others - doesn't look right to my eyes - or is it a shadow effect in the photograph?

Another thing you could try is to cut very small rubber washers, either from thin rubber sheet or small slivers of the gasket rubber, and place them between the front plate and body when refitting the screws, so that the clamping effect has some hold-off/relief/gap, and adjustment possible.


It's a reflection in the inner perimeter of the chromed ring. The gasket is well seated below the mother-of-pear, it's absolutely invisible from the exterior.

I could indeed try to release a bit the front screws and see what happens when the pressure over the gaskets decreases, but this will also push the diaphragm towards the needlebar, it will no longer be balanced in neutral position, so one effect could mask the other.


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 Post subject: Re: Gilbert portable.
PostPosted: Mon Aug 21, 2017 10:26 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
CarlosV wrote:
Marco, the aluminum diaphragms that work under compression are those with the radial folds that act as springs, like the HMV 5a/5B, the Victor orthophonic. The rim of the diaphragm in these soundboxes is clamped to the frame and the inner part is the one that moves. This Gilbert looks more like the EMG diaphragm, it has a small fold near the center but to me for it to perform well the whole diameter needs to move (it is also quite thick aluminum), therefore if it gets clamped it will not perform well (like a mica diaphragm). I have an old stock tubing that is very pliable, I bought in an auction but I don't really know where it was purchased.

I also got the same impression: that this diaphragm looks like one of the "electric/orthophonic" era, but behaves more like the old mica types. Indeed it is mounted pretty much like mica ones (but Columbia Viva-Tonals also are, with tubing gaskets etc., but they're very flexible instead). Thanks for offering the alternative tubing, I have replied to your PM.


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 Post subject: Re: Gilbert portable.
PostPosted: Tue Aug 22, 2017 1:59 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 551
Location: Italy
As anticipated, I tried to release some pressure from the gaskets by unscrewing the front retaining ring. The experiment didn't give impressive results: I believe there was a bit more bass and balanced tone overall, but definitely not a noticeable increase of volume.

I'm going ahead in the restoration of the machine. I polished the arm, which came out very fine. There was a very small crack on top of the elbow, right in front of the threaded hinge. Inspecting the arm from the inside, I think it is pretty evident that at least this section was not made with a pipe, but it's a folded and soldered sheet of metal. I'm thus quite persuaded that this was not a crack, but an area in which the sheet's ends were just a bit too short to meet each other. Just to make sure that the seam will not open further in the future, I tried to solder it. Inside all I can do was to leave an awful ball of tin, but the metal streamed very nicely through the seam and the solder is quite all right seen from the outside.


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