[TenTec] 238A-C roller inductor

Wed Jun 19 18:04:21 EDT 2013

Thanks for the input, Bob. My problem (as a Novice) at the time, was
that tuning on low power and obtaining resonance, does nothing to
consider VSWR and heating effects.

The antenna impediance and antenna efficiency are key in radiating a
signal as opposed to an antenna merely being an electric heater.

Much has been written about matching and a dummy load is a pretty
good match; however, it's obviously about the entire set-up and
creating a good antenna system.

My intent was not to be critical of roller inductor tuners, but
rather to illustrate how easy it is for a newbie to go astray.

Thanks for reading ES 73,

de Phil - N8PS

-----

Quoting Bob McGraw - K4TAX <RMcGraw at Blomand.net>:

> I agree Phil, most rollers just need cleaning and adjusting such  
> that the rolling contact doesn't loose contact with the roller coil.  
>  Wiping them down with a clean lint free cloth and with a very small  
> amount of contact cleaner such as Cramolin or DeOxit seems to  
> restore them for years.
>
> As to tuner ratings,  keep in mind there are limits to the  
> impedances they will match.   I've found that even though they may  
> match a wide range of impedances, this does not imply they will  
> handle the rated power over that range.  See recent test reports  
> published by ARRL for some of the more popular tuners.  Note the  
> loss factor too.  That loss is directly converted to heat and it is  
> this heat which is dissipated by the tuner components. For example  
> at 1500 watts and a tuner having a loss of 25% the dissipated heat  
> would be about 375 watts to be dissipated by the components in the  
> tuner.  This 25% figure is not out of bounds for some loads and  
> tuners but their ability to handle the power dissipated is  
> questionable.
>
> Two recent tuners reviewed by ARRL, July 2013 QST, show loss figures  
> of  18% on 10M with a SWR of 16:1 or 800 ohms.  One other tuner  
> shows a loss of 15% on 160M with a 2:1 SWR or 25 ohms and a 14% loss  
> on 10M with a 16:1 SWR or 800 ohms.  Another test condition/tuner  
> data shows a 33% loss on 160M with a 2:1 SWR or 25 ohms and a 28%  
> loss on 10M with a SWR of 2:1 or 25 ohms.  Also see test results  
> published in QST, March 2013.
>
> My experience is that a 2KW PEP rated tuner is capable of handling  
> about 500 watts.   Agreed, it will handle SSB PEP values at many but  
> not all impedance loads to 1500 watts or so.  Put in a 1500 watt  
> carrier and watch for that tell tale odor of heating components and  
> the following smoke emissions!
>
> While we may think antennas present a 50 ohm load, in fact based on  
> height above ground, they more typically present loads in the order  
> of 12 to 35 ohms.  This impedance demands a higher current than a  
> load of say 100 to 500 ohms where the issue there is voltage.
>
> A few noted values:
> 10 ohms @ 1500 watts = 122V @ 12.2A
> 12 ohms @ 1500 watts = 134V @ 11.2A
> 25 ohms @ 1500 watts = 193V @ 7.4 A
> 50 ohms @ 1500 watts = 273V @ 5.4 A
> 100 ohms @ 1500 watts = 387V @ 3.8 A
> 500 ohms @ 1500 watts = 866V @ 1.7 A
> 1000 ohms @ 1500 watts = 1224V @ 1.2 A
>
> Add in reactive components of the typical nature and things get out  
> to bounds quickly.  Based on ARRL test results it is clear that  
> tuners seem to handle higher impedance loads better and more  
> efficiently than low impedance loads.
>
> 73
> Bob, K4TAX
>
>
>
>
> ----- Original Message ----- From: "Phil Sussman" <psussman at pactor.com>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>; "Wade  
> Staggs" <tvman1954 at gmail.com>
> Sent: Wednesday, June 19, 2013 10:14 AM
> Subject: Re: [TenTec] 238A-C roller inductor
>
>
>> Ah, my first days with a roller inductor tuner. "Roller Inductors don't
>> wear out .. they just get dirty contacts."
>>
>> Oh well, they do MELT as my MFJ did. All I did (after I tuned it on low
>> power) was apply 400w on 80m into a G5RV. Whoops. Smoke !! It was rated 2Kw.
>>
>> Went out and bought a Nye-Viking M-B-V and still using it to this day.
>> Years later -- no problems.
>>
>> 73 de Phil - N8PS
>>
>> PS. Golly your 'roller inductor' story brought back some old memories,
>> or rather I should say, foul smells of melted components. Whew - PU !!
>>
>> ----
>>
>> Quoting Wade Staggs <tvman1954 at gmail.com>:
>>
>>> I must agree with Bob/K4TAX ... My MFJ-989C Tuner is not built anywhere
>>> close to the quality of your Tuner. I bought it new in 1995 and by never
>>> tuning under high power, the only issue with it was from being not used for
>>> a couple of years. When it came out of Moth Balls and returned to service.
>>> After a good going over and cleaning with DeOxit, all is well. I also
>>> checked all mechanical pieces for dried lubricants and used a light oil
>>> where needed. Most Roller Inductors don't Wear Out .... they just get Dirty
>>> Contacts and such.
>>>
>>> 73 from Wade/KJ4WS
>>>
>>> On Tue, Jun 18, 2013 at 3:27 PM, denton sprague  
>>> <denton at oregontrail.net>wrote:
>>>
>>>> Got a nice used(again)238A TT tuner and the roller inductor is getting a
>>>> tad long in the tooth…
>>>> Priced a new one out of TT but can't justify it right now.
>>>> Has anyone installed an aftermarket inductor in  their TT tuner…if so, can
>>>> you send me the details. Thanks...
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