[Test-Equipment] Bird Termaline Question - Update (long)

[Howard Weeks]

Brian,

Thanks for the comment! Wasn't sure anyone read it.

I understand about the impedance issue with it. At that time, I had been 
using a light bulb for a dummy load. So, almost anything would have 
worked for me in the manner that I was using it. Today, it sets on the 
floor behind my operating position and is connected to the antenna 
switch. If needed, I can switch to it and tune up into it.

I have access to an analyzer that will scan R and impedance up to about 
a GHz. I also have several other Bird loads including one that is rated 
at a KW. I did scan those and all were flat all the way up to 1 GHz. 
Didn't think about doing the 500 watt unit.

This discussion has been interesting, and, hopefully, I will learn 
something from it!

73's,

Howard K5JCP



On 2/8/2017 2:36 AM, Brian wrote:
> Hello Howard,
>
> That circular clamp adds diameter to the tubular resistor. The conic
> section dimension at that point directly affects the impedance. Your
> measurement of 49 Ohm is not so important as the impedance - how about
> measuring that at a few different frequencies?
>
> I have had similar problems with cracked tubular resistors for use in
> oil-cooled dummy loads. My solution was to infiltrate the crack with a
> silver-loaded Araldite (R), the type auto electricians use to repair the
> elements in heated windscreens that have been damaged by women scraping
> their diamond-encrusted fingers over the screen to remove condensation.
> I achieved the nominal resistance and there was no observable effect on
> impedance.
>
> 73 de Brian, VK2GCE.
>
> On Wednesday, February 08, 2017 6:35 AM, you said:
>
> Back around 1962 or so, I came by a 500 watt Bird Termaline load.
> According to an ohmmeter, it was reading high - well over 50 ohms but
> less than 100. I do not remember exactly what it was.
>
> I stood the load on it's back end, loosened the clamp ring and removed
> it from the case. Lost a little oil in the process. The problem was a
> crack in the load resistor up near the top or feed point end. Since the
> coating on the resistor was conductive, I put a small stainless radiator
> clamp (about 1/2" wide) over the crack and tightened it. The resistance
> went to about 49 ohms or so and I put it back together with a little
> additional mineral oil. I still have that load and it is still working.
> The slightly low resistance doesn't make any practical difference in the
> normal use of it.
>
> Howard K5JCP in GA
>
>
> ______________________________________________________________
> Test-Equipment mailing list
> Home: http://mailman.qth.net/mailman/listinfo/test-equipment
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Test-Equipment at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>