Hello,

I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

73's DX

Marcelo
LW3EOV/GB

wrote in message
...
Hello,

I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

73's DX

Marcelo
LW3EOV/GB

Hi Marcelo,
I think that 0.5 centimeter is a typo, it seems to thick, I think it should
say millimeters.
As a reference compare the thickness of the brass nuts to the plate
thickness.
Mike

I wouldn't call 0.5 cm "foil"...more like aluminum "plate"...that's
almost 3/16 inch thick. Try http://www.aircraftspruce.com

Scott


wrote:
Hello,

I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

73's DX

Marcelo
LW3EOV/GB


--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

In article ,
wrote:

I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

I think that figure, cited on the web site, must certainly be a
typographical error. There's no way that aluminum sheet which is 0.5
centimeters (5 millimeters) thick would make sense in this application.

I'd believe that it's supposed to be 0.5 mm (rather than 0.5 cm). I
can't offer a specific source, since I'm in the United States, but a
well-stocked hardware store might carry something of about that
thickness. When I look up aluminum sheeting at www.use-enco.com (a
U.S. mailorder supplier) the thinnest I see is 0.032", which is around
..8 mm I believe.

I do have one specific concern about the butterfly capacitor design
you're interested in. Capacitors used for resonating small magnetic
transmitting loop antennas need to have low resistive losses, due to
the high Q and the high currents in the loop. Butterfly capacitors
are often preferred to typical stator/rotor capacitors because they
have no "wiping" contacts (which have a relatively small contact area
and thus potentially a relatively high resistance). The most-favored
type use an all-welded or all-soldered construction, in order to
ensure a low-resistance path to all of the plates.

Unfortunately, the homebrew cap you're looking at uses threaded brass
rods, brass nuts, and aluminum plates. None of the connections are
soldered. The connections to the stator plates will be
interference/friction mating (i.e. brass nut, tightened onto aluminum
plate) and I'd be concerned that the aluminum will soon oxidize and
that the connections may rise in resistance, leading to increased
losses over time.

This issue could be largely eliminated if you were to use sheet brass,
rather than sheet aluminum, for the stator plates. You could then
flux and solder the rods, nuts, and plates together (before installing
the acrylic endplates, of course :-) and ensure a solid, reliable,
low-resistance current path.

I think you could continue to use aluminum for the rotor plates, if
you wish, since the current flow will be across the plate and there
will be little or no need for current flow between adjacent plates.

If you do use aluminum plates for the stators,, I'd consider adding a
thin smear of a conductive aluminum-compatible anti-oxidant grease
(Penetrox, NoAlOx, or a similar product) around the hole in each
stator plate, before tightening down the brass nuts. This would help
make a reliable contact, and exclude oxygen from the aluminum surface.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

Make contact with the Flight Refuelling Amateur Radio Society
(www.frars.org.uk), based near Poole. They will tell you where to find
sheet metal in Dorset.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Nov 27, 1:41 am, (Dave Platt) wrote:
In article ,

wrote:
I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

I think that figure, cited on the web site, must certainly be a
typographical error. There's no way that aluminum sheet which is 0.5
centimeters (5 millimeters) thick would make sense in this application.

I'd believe that it's supposed to be 0.5 mm (rather than 0.5 cm). I
can't offer a specific source, since I'm in the United States, but a
well-stocked hardware store might carry something of about that
thickness. When I look up aluminum sheeting atwww.use-enco.com(a
U.S. mailorder supplier) the thinnest I see is 0.032", which is around
.8 mm I believe.

I do have one specific concern about the butterfly capacitor design
you're interested in. Capacitors used for resonating small magnetic
transmitting loop antennas need to have low resistive losses, due to
the high Q and the high currents in the loop. Butterfly capacitors
are often preferred to typical stator/rotor capacitors because they
have no "wiping" contacts (which have a relatively small contact area
and thus potentially a relatively high resistance). The most-favored
type use an all-welded or all-soldered construction, in order to
ensure a low-resistance path to all of the plates.

Unfortunately, the homebrew cap you're looking at uses threaded brass
rods, brass nuts, and aluminum plates. None of the connections are
soldered. The connections to the stator plates will be
interference/friction mating (i.e. brass nut, tightened onto aluminum
plate) and I'd be concerned that the aluminum will soon oxidize and
that the connections may rise in resistance, leading to increased
losses over time.

This issue could be largely eliminated if you were to use sheet brass,
rather than sheet aluminum, for the stator plates. You could then
flux and solder the rods, nuts, and plates together (before installing
the acrylic endplates, of course :-) and ensure a solid, reliable,
low-resistance current path.

I think you could continue to use aluminum for the rotor plates, if
you wish, since the current flow will be across the plate and there
will be little or no need for current flow between adjacent plates.

If you do use aluminum plates for the stators,, I'd consider adding a
thin smear of a conductive aluminum-compatible anti-oxidant grease
(Penetrox, NoAlOx, or a similar product) around the hole in each
stator plate, before tightening down the brass nuts. This would help
make a reliable contact, and exclude oxygen from the aluminum surface.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Thanks for taking the time to give me an explanation, I will try to
find sheet brass, but still don't know where in UK.

On Nov 27, 7:30 am, Ian White GM3SEK wrote:
I found this very nice website with a section about Homebrew Butterfly
Capacitor with many photographs.

http://hps.infolink.com.br/py1ahd/gallery21.htm

Does anybody knows where in UK (preferrable in Dorset or London) can I
get aluminum foil, 0.5 centimeters thickness?

Make contact with the Flight Refuelling Amateur Radio Society
(www.frars.org.uk), based near Poole. They will tell you where to find
sheet metal in Dorset.

--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek

Thanks Ian, I sent an email to M1FBB, Steve Smale, from the Flight
Refuelling Amateur Radio Society.

wrote in message
...
[...]

Thanks for taking the time to give me an explanation, I will try to
find sheet brass, but still don't know where in UK.

I buy Aluminium and Brass sheet from ebay. Last buy was item number
160183295588.
Not cheap though!. Probably much easier to buy a TF801 for a fiver and
dismantle/rebuild the magnificent Gold and silver plated turret capacitors.
There's also a bonus of about 2 square feet of Gold plated, brass sheeting
in there.

On Nov 26, 8:41 pm, (Dave Platt) wrote:
Unfortunately, the homebrew cap you're looking at uses threaded brass
rods, brass nuts, and aluminum plates. None of the connections are
soldered. The connections to the stator plates will be
interference/friction mating (i.e. brass nut, tightened onto aluminum
plate) and I'd be concerned that the aluminum will soon oxidize and
that the connections may rise in resistance, leading to increased
losses over time.

This issue could be largely eliminated if you were to use sheet brass,
rather than sheet aluminum, for the stator plates. You could then
flux and solder the rods, nuts, and plates together (before installing
the acrylic endplates, of course :-) and ensure a solid, reliable,
low-resistance current path.

In the real world, most non-miniature variable capacitors were made
with spacers and plates that weren't soldered all together, and
generally didn't use star washers or anything except at the connecting
posts. But these are generally either all-brass, all-aluminum, all-
steel, etc., and not a mismash of different materials. You don't
explicitly say so, Dave, but are you implying that it's the dissimilar
materials that are the problem, or that it's the use of aluminum? My
personal taste would be to make it out of all-brass.

After the 50's, for the miniature variable capacitors, they seem to be
made out of material that has been silver-soldered together without
any explicit spacer components. (Maybe brazed or spot-welded, in some
cases.) This seems to be either an improvement made for VHF/UHF work
(remember when 50MHz was UHF?) or an admission that using spacers
doesn't make economic sense when components are so tiny.

Tim.

In article ,
Tim Shoppa wrote:

In the real world, most non-miniature variable capacitors were made
with spacers and plates that weren't soldered all together, and
generally didn't use star washers or anything except at the connecting
posts. But these are generally either all-brass, all-aluminum, all-
steel, etc., and not a mismash of different materials. You don't
explicitly say so, Dave, but are you implying that it's the dissimilar
materials that are the problem, or that it's the use of aluminum?

It's a combination of both, I think.

A cap of this sort would work quite nicely indeed if it were made out
of aluminum, and welded together. I believe that such capacitors are
available even today (perhaps on special order). Aluminum's
conductivity is certainly high enough, and the thin layer of aluminum
oxide on the surface would have no effect on the cap's usability.

The biggest problem with a hybrid aluminum/brass capacitor is that
it's hard to get a reliable, low-resistance bond between the two
metals. It's certainly not impossible - there are some fluxes and
solders which can bond to aluminum - but it's not necessarily easy for
the hobbyist to make this work reliably.

Non-welded aluminum air-variable capacitors seem to work find in most
applications... but in most applications, the currents flowing through
the cap are relatively low, the circuit impedances are relatively
high, and thus the resistive losses in the plate/spacer connections
are negligible. In magloop transmitting antennas, the radiation
resistance is small (often just a fraction of an ohm) and the
resistive losses in the tuning capacitor can significantly effect the
efficiency of the antenna.

My
personal taste would be to make it out of all-brass.

After the 50's, for the miniature variable capacitors, they seem to be
made out of material that has been silver-soldered together without
any explicit spacer components. (Maybe brazed or spot-welded, in some
cases.) This seems to be either an improvement made for VHF/UHF work
(remember when 50MHz was UHF?) or an admission that using spacers
doesn't make economic sense when components are so tiny.

The highest-quality seem to use silver-plated brass, soldered or
welded together. This would assure a good electrical connection, and
I believe that this combination of materials and methods also helps
reduce the tendency of the capacitor to drift in value as a result of
temperature changes, or exhibit microphonic effects. People who build
low-drift VFOs seem to favor this style of air-variable capacitor.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!