Making stepped mica diaphragms?

[Victrolaboy]

I want to try using a stepped mica diaphragm in my model C reproducer. Can anyone give me tips on how to do this and make it look good? I'm a perfectionist so I like things to be neat.

[Victrolaboy]

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[Victrolaboy]

Never mind I figured it out. I cut the mica with a circle cutter that is basically a compas with a blade. I glued the layers together with contact cement which dries semi flexible. The diaphragm shown in the picture has only one step.

[Roaring20s]

What is the result in the sound by doing this?

James.

[Victrolaboy]

Well, I think it sounds 100 times better than the copper diaphragms. The sound from copper diaphragms are pretty darn good but compared to the stepped mica, the mica has a brighter tone to it and it's a bit louder than the copper. I will be doing more experiments by adding more steps to the mica. They key to rebuilding these reproducers so they sound their best is to make sure that the diaphragm isn't clamped down tight between the gaskets. It only needs to be tight enough so that it's airtight.

[Chuck]

Nick,

Nice job on the stepped mica! Shawn Borri is the
resident expert on these. He too has made many versions
of them, usually the ones he talks about use at least
3 steps.

The idea of it is to make the center portion of it
a bit stiffer than the outside. Having the center thick
with the outside thin allows it to act more like
a piston for low frequencies, hence the bass response
will be better. That is the theory anyway.

But hey nice job and yes, contact cement works well
for some things, but it's not ever coming apart again
any time soon either.

Chuck

[Victrolaboy]

Chuck,
I didn't think about that. What about shellac for gluing the steps together? I will continue to experiment with more steps this is only diaphragm #3!

[Chuck]

Nick,

If I was doing it I'd first try using stratena glue.
That stuff is a clear liquid and it dries clear.
It's the old old stuff they used back when this
equipment was all new.
It is a gelatin based glue, it comes loose
by soaking in water.

Peter Wall was making it and selling it on ebay for
a couple bucks per bottle. I got a few bottles of it
back in 2009/2010 time frame.

I've used it with great success and very pleasing results
on a few recorder rebuilds. I even had to take one
apart again a few times for fine adjustments, and it
is a breeze, just place a couple of damp Q-tips along
side the parts to be unglued and wait about half
an hour and they just slide apart.

Up until quite recently this stratena glue could be
found on ebay by simply typing in the search for it.
But, I have lately heard reports that folks have tried
finding it with no luck.

Peter's ebay username was Gramophile or some such
thing. I hope he's still making it because it's really
good stuff to have around. I think it would be just
the thing for stepped mica.

Also consider superglue but again that will be
permanent. Shellac, yes too because the mica can
stand the heat required to melt it.

And also, let us not forget George Vollema's
trick of dissolving some flake shellac in denatured
alcohol to make a saturated solution which will take
no more shellac. That stuff also makes great glue
because the shellac is carried along by the alcohol
and then the alcohol evaporates.

I made a test batch of that stuff and then glued up
a few tests of copper to aluminum and it seems to
hold quite well, but so far I've never yet used it
for anything other than those few tests.

So, there's a few ideas anyway.

Chuck

[EarlH]

Have any of you used burnt shellac? That was a pretty common cement in those days. Probably more or less the same as what you are describing by using very thick shellac, but you light it on fire in something like a tuna can and burn the alcohol off until it's pretty thick. That's what I've always used when I've attached Music Master horns to the collar. If you need it back apart alcohol or ammonia will dissolve it. It's used a lot in player piano work to make air tight joints ect. It's kind of slow to dry though, but once it sets up it will hold very well.

[phonojim]

Regular white shellac works well for me. One thing I noticed about these is that the largest diameter layer of the diaphragm is thinner than the single layer micas that you buy today. I rebuilt an Edison stepped mica and had to split a new diaphragm with a razor blade to get the same thickness as the old one. IIRC, it needed to be split by about half. If you don't have a micrometer, you need to get one for this kind of work.

Jim