It's not just the temperature, but the physical endurance and the electrical
properties as well. Remember that this stuff will be exposed to high RF and
magnetic fields. I once had the base of an RF choke in a 4-1000 amplifier
expoxied to a ceramic standoff insulator. Once night during a contest, the
epoxy exploded and coated the inside of the amp with hot yellow goo (the amp
continued to run!). So, we know through the experience of many who have
made these types of coils that Scotch 27 glass tape works as intended.
Substituting something else could cause problems like melting, a fire or
small explosion! And YES, balun coils do get quite hot when running into
high power, high SWR like the output of a tuner.
Mike, W1NR
----- Original Message -----
From: "Will Matney" <craxd1@verizon.net>
To: <amps@contesting.com>
Sent: Tuesday, June 13, 2006 2:31 PM
Subject: Re: [Amps] glass tape scotch 27
> What I'm wondering is why one would need a tape rated at 130 C (266 F)?
> The core should not get no where near that hot, maybe just warm to the
> touch which would be around 100-110 F (37.7-43.3C). Ferrite supposed to be
> non-conductive which would only leave sharp corners which can be removed
> easily with a piece of emory cloth if they have them. You can also place a
> wood dowell through the center of the toroid and use a wire brush wheel on
> a grinder to remove them very quickly from the O.D.. I generally just keep
> a piece of emory cloth on the bench and smooth them that way. It don't
> take too long to do it. I've seen many cores, both iron powder (which most
> has a painted coating), and ferrite without tape that has lasted for
> years. I wouldn't doubt that regular tape like the filament tape I
> mentioned would work just fine. Matter of fact, I know a company that used
> that tape to install the RF power meter in an amp which was mounted where
> the tubes were close, and heat actually mel
> ted the meter back when the fan quit. The tape was still ok. I cant see
> one vibrating enough to cause this either. If it does, something like the
> blower or fan is way out of balance, and ought to be replaced. The newer
> varnishes on magnet wire is pretty tough, especially if it has Teflon
> insulation like Teflon hook up wire. On toroids, you need all the space
> you can get to hold the wire if it will be a good amount, so a thin tape
> ought to be used if possible like Kapton. That is if any need be used at
> all like a good amount which does not. On input tune cores, tape means a
> lot of space where they are small. On output tank coil toroids for 80 or
> 160 meters, I've seen both taped and non-taped used. I just can't see
> where this expensive tape would be needed here for this purpose.
>
> Best,
>
> Will
>
> *********** REPLY SEPARATOR ***********
>
> On 6/13/06 at 7:14 AM tim jenkins wrote:
>
>>scotch 27 is high temp with thermosetting pressure-sensitive ashesive and
>>operates at class b 130 deg C ( 266 deg F) temp. tim kv4bk
>>scotch 27 glass cloth electrical tape
>>
>>kv4bk @ amps4u
>>
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>
>
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