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@pactor.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>; "Wade Staggs"
<tvman1954@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@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@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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