Re: PVC vs. sonotube, (was wondering ) (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 03 Jun 2007 12:53:17 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: PVC vs. sonotube, (was wondering ) (fwd)

I wanted to add some things about sonotube that came to mind after I 
sent this.

I am not advocating the use of sonotube, just telling my experience. 
Sonotube has been said to cause racing sparks and things of that nature. 
That is ridiculous. A poorly sealed sonotube form will absorb moisture 
and cause a big change in the dielectric. The moisture content appears 
as though the coil was wound on a metal cylinder. This effectively 
changes the tuning as it is a large external capacitance seen to the 
secondary. Thus, tuning changes. The coil is no longer in tune and 
racing sparks can definitely occur. Of course, if the sonotube was 
properly sealed to prevent moisture absorption into the fibers, this 
would never occur. It's that simple.

Although sonotube is thin and does not weigh much, it is also harder to 
make end caps for to mount large top loads onto. I did this by gluing in 
top and bottom disc (using dowels into the sides of the disc) and 
running a 2" pvc pipe inside the coil the entire length which had a 
press fit to the 2" hole in the center of each disc. Granted, this 
worked to make the sonotube coil very rigid and capable of mounting top 
load objects onto, but it's not ideal.

If I were to again build a large coil, I would likely choose pvc (or 
something other than cardboard) because of the mechanical machinability 
and the fact that pvc is a much stronger form for these kind of things.

I wanted to clarify that I dispute the performance issue of sonotube, 
but I'm all for the use of other form materials from a mechanical 
standpoint.

Take care,
Bart

Barton B. Anderson wrote:

> Agree with John here except in the sonotube category. In my use of 
> sonotube, I had no problems with heating or performance. I imagine 
> much depends on the quality of the sonotube itself (impurities or lack 
> of). When I built my sonotube, I thinned out varnish (varnish and 
> paint thinner) so that I had a very liquefied coating. I coated the 
> inside and out several times with the thinned varnish (wanting it to 
> soak into the cardboard) then finished off with a couple coats of 
> unthinned varnish. Wound the coil and then coated it with thick marine 
> spar varnish. Coil ran great.
>
> I know some coilers have had great success with sonotube and some 
> coilers have had miserable failures. I'm not sure why the division 
> exists unless prep is part of it or if it's just the type of sonotube. 
> My sonotube was called Quikrete and I think I purchased it at a Home 
> Depot in Minnesota at the time.
>
> For small coils under 8" diameter, pvc would be my choice. But as the 
> coil gets larger, pvc gets "heavy" and thick. Sonotube does have the 
> advantage of size vs. weight, but it is also more difficult to machine 
> end caps for. If sonotube is not treated, it will acclimate with the 
> weather and humid climates will definitely have problems (as Terry 
> Fritz found out while measuring sonotube and saw a major changes when 
> it rained).
>
> Take care,
> Bart
>
> Tesla list wrote:
>
>>Original poster: List moderator <mod1@xxxxxxxxxx>
>>
>>
>>
>>---------- Forwarded message ----------
>>Date: Sun, 3 Jun 2007 13:15:40 EDT
>>From: FutureT@xxxxxxx
>>To: tesla@xxxxxxxxxx
>>Subject: Re: PVC vs. sonotube, (was wondering )
>>
>> 
>>In a message dated 6/3/2007 12:01:37 P.M. US Eastern Standard Time,  
>>tesla@xxxxxxxxxx writes:
>>
>>  
>>
>>>Hi  all,
>>>     I know the best material to use as a coil  form would be either HDPE 
>>>    
>>>
>>or styrene, but if pvc is the best available  choice,  would milling grooves 
>>lenthwise down the form make it less  lossy?   I'm sure it would be a pain in 
>>the butt to do, but wonder  if it would be worth the trouble.
>>  
>>
>>>     Also,  I  cannot seem to find info on whether a sonotube would be a 
>>>    
>>>
>>better choiice to  reduce losses in the form.
>>  
>>
>>>   Mike
>>>    
>>>
>>
>>
>>
>>Mike,
>> 
>>In reality, PVC is not very lossy for TC use.  You won't see any  difference 
>>in performance using PVC 
>>vs. styrene in a disruptive TC.  Even for a tube coil, which is more  
>>sensitive to losses, you
>>probably won't see a difference in performance.  The biggest potential  
>>problem with PVC
>>is carbon tracking and burning.  This only occurs if the coil is  overcoupled 
>>or subject to
>>flashovers, arcing, etc.  Some folks advocate baking and sealing the  pvc to 
>>keep moisture
>>out.  In 90% of the cases, folks don't bother with that.  So to  answer your 
>>question milling
>>grooves is not worth the trouble.   Sonotube can be very bad  depending on 
>>how it's made.
>>I tried it for a tube coil and it got hot.  Performance was  miserable.
>> 
>>John
>>
>>
>>
>>************************************** See what's free at http://www.aol.com.
>>
>>
>>
>>
>>
>>  
>>