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Poli 'Micro Tromba' brass membranes

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Poli 'Micro Tromba' brass membranes

Postby vegansydney » Sat Jan 09, 2021 4:42 am

Does anyone have any advice for fitting the brass membranes to Poli 'Micro Tromba' horns?

I've just replaced a set along with the gaskets (both NOS) and I'm still not getting a tone from the horns. The foot pump is working and I can feel air getting getting through to the horns, but no sound. Although I've got a few sets of these horns (they're great for waking up NYC taxi & ride share drivers) I've never replaced the membranes. Any advice recommended. Thanks!
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Re: Poli 'Micro Tromba' brass membranes

Postby Warkton Tornado No.1 » Sat Jan 09, 2021 2:07 pm

I would suspect that you might be able to show them to a wind instrument player, or a shop, that will know just how to tweak as technically, they are reeds.

Some people just have the knack.

As a kid, I could never get those blades of grass held between thumbs to make a note, whereas others could. And they could make those piercing wolf whistles as well. The b@st@rds!

I'm over it now.......almost ;)
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Re: Poli 'Micro Tromba' brass membranes

Postby gaz_powell » Sat Jan 09, 2021 3:19 pm

Warkton Tornado No.1 wrote:
As a kid, I could never get those blades of grass held between thumbs to make a note, whereas others could. And they could make those piercing wolf whistles as well. The b@st@rds!

I'm over it now.......almost ;)


You and me both... But a can still make a fart noise with my arm pit...

I need to get out to the pub....
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Re: Poli 'Micro Tromba' brass membranes

Postby Warkton Tornado No.1 » Sun Jan 10, 2021 12:52 am

gaz_powell wrote:
Warkton Tornado No.1 wrote:
As a kid, I could never get those blades of grass held between thumbs to make a note, whereas others could. And they could make those piercing wolf whistles as well. The b@st@rds!

I'm over it now.......almost ;)


You and me both... But a can still make a fart noise with my arm pit...

I need to get out to the pub....


I used to be able to jump up into the air & let one go @ the peak of the jump. I don't know whether I dare even try that these days. Not that I'm an old 'slack @rse'. It would be getting the timing just right that'd be difficult......
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Re: Poli 'Micro Tromba' brass membranes

Postby missing lynx » Sun Jan 10, 2021 12:44 pm

Is the diaphragm the right way round? also the tightness of the clamping plate holding the diaphragm in will affect it as well as how the horns are clamped to your scooter. Also try a bike pump (gently) to see the original bulb is producing enough puff
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Re: Poli 'Micro Tromba' brass membranes

Postby vegansydney » Sun Jan 10, 2021 3:46 pm

missing lynx wrote:Is the diaphragm the right way round?


Great point. I didn't realize they were sided. I'll see if swapping them around makes a difference. I can also check the pump by connecting horns to a known working pump on another scooter. Thanks for the advice!
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