Don:
The material I used is Dow-Corning 748, identified as a "non corrosive"
"food grade" product. If you find yourself in need of an
electronics-compatible sealant, I can recommend it. I ordered the D-C
748 from McMaster-Carr, and here's how they describe it:
*748 Noncorrosive— *Use where low odor is desirable. Bonds to metal,
plastic, glass, and rigid PVC. Resists moisture and weather and works
with corrosion-sensitive electrical and electronic equipment. Begins to
harden in 30 minutes. Temp. range is -67° to +350° F. Complies with FDA
regulation 21 CFR 177.2600 covering indirect food contact. UL listed.
A 3 ounce tube is $7.48, so you will pay quite a bit more than the
hardware store stuff, but it does exactly what you need in an electronic
sealant. There are other D-C electronic sealants with different
viscosity. The 748 is similar to standard RTV in viscosity and handling.
Jack K8ZOA
www.cliftonlaboratories.com
Don Wilhelm wrote:
Jack,
Thanks for the additional comments.
The original post had specified the GE Silicone II adhesive that he
had on hand. In my experience that is not a 'properly selected
silicon compound'.
The last tube I had of that I started to use on some terminals on an
aluminum vertical - well I had a copper wire attached, and it turned a
sickly green within two weeks. I had to scrape it all off (a tough
job), use new hardware and wire. I vowed never to use any that was
not specifically marked as 'electronic grade'.
73,
Don W3FPR
-----Original Message-----
Don:
I agree with you that nothing is required to secure the toroids
to the K2's PCB, it is not the case that a properly selected
silicon compound causes damage.
"Neutral cure" or "electronic grade" silicon will not cause
damage, as it sets up without emitting the acetic acid given off
with the typical RTV found in hardware stores. I ran tests last
fall to determine the effect of RTV upon Q and inductance of 4uH
toroids, wound on T50-2 cores for the Z10010 4.915 MHz bandpass
filter I provide along with the Z90/91 panadapters, where the
purchaser plans to use it with a K2. To the best of my ability to
read the HP4342A Q-meter, there were no changes in Q or inductance
after the neutral cure silicon rubber cured. The particular
product I used was a Dow-Corning compound, which gave off a faint
smell reminiscent of peppermint. About half the filters I built
use it to secure the toroids to the PCB. I abandoned it half-way
into the production run as (a) the wire leads, it turned out, were
adequate and (b) it was extremely difficult to apply without
getting it all over the PCB. I wound up doing post-assembly work
with an Xacto knife, trimming pieces of cured RTV from locations
they did not belong.
I also ran tests to determine the effect of Q-dope on the same
inductors and found that the effects were somewhere between
negligible and the limit of my ability to measure. (For the newer
hams, Q-dope is used to secure windings to a coil form and is
basically polystyrene dissolved in toluene.) I decided to Q-dope
the majority of the inductors I wound for about 35 filters (140
total toroids) as method of assisting the long term stability of
the Z10010 filter, which is a bit touchy if the flat nose and
symmetrical flanks are to be maintained. A few filters were
assembled without Q-dope as a comparison, and they seem to work
just as well.
Still, as I said at the start of this message, I agree 100% with
Don't recommendations--don't use either RTV or Q-dope in your K2
assembly.
Jack K8ZOA
www.cliftonlaboratories.com
Don Wilhelm wrote:
Mike,
Use NOTHING to secure the toroids other than their leads. In the 7+ years
of the life of the K2, I have never heard of a failure die to a fractured
toroid lead, and there is one that I know of (I built it) that served for a
couple years as a mobile rig in the cab of an 18 wheeler - I am certain that
one saw more than normal shock and vibration.
Any securing compounds can cause damage - be particularly careful of the
silicone glues. The GE Silicone II that I have found smells like vinegar
and will cause a green corrosion mess when in contact with copper (could
even destroy the K2)
Elecraft recommends no fixatives for the toroids, and the use of them may
void the warranty, so go forth with it at your own peril.
73,
Don W3FPR
-----Original Message-----
All,
My K2, serial no. 05625 is complete and has been on the air for three
weeks today, but I'm still in the process of adding accessories. I've
mostly run it on 80 and 40 m with excellent results.
One question I have for the group- Has anyone found a need for
protecting the vertically mounted toroid inductors from mechanical shock
events during portable operations? If so, what staking material is
recommended? I am concerned about degrading exposed conductors with
anything I might use for an adhesive. I think the GE Silicone II
adhesive I have on hand is used for preventing corona or ionization
around high voltage terminals so maybe it would be a good candidate?
73
Mike Mussler
AI8Z
K2 serial 05625
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