[TenTec] 238A-C roller inductor

Wed Jun 19 12:18:56 EDT 2013

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...
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
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