Jim,
i too have heard that any more than one tuner can cause serious 
problems.  If you have one, perhaps you could use one tuner and then 
the other in to a dummy load and see what the power output looks 
like.  If you can add a few extra watts it may not help too much but 
certainly won't hurt.  And it always feels good to get the most out of the rig!
pat, K9JAUAt 08:23 PM 11/26/2014, you wrote:
>I am using the internal tuner in my Ts 590 but still have my
>small external tuner in line that I used with the TS 480.  I have
>noticed that I don't get much action from the external tuner like
>I used to get when it was connected to the 480.  Seems like the
>internal tuner in the 590 is handling most or all of the tuning.
>My question is, can I take the external tuner out of the line?
>Thanks for your thoughts, Jim WA6EKS
>
>  ----- Original Message -----
>From: Bob Tinney <[log in to unmask]
>To: [log in to unmask]
>Date sent: Wed, 26 Nov 2014 21:15:50 -0500
>Subject: Re: SWR, antenna tuners, and reflected power
>
>I have to add something here,  I used to think that you had to
>have a
>perfect match to maximize efficiency.  But I now realize that if
>you
>have a good, wide range, antenna tuner, you can match almost
>anything.
>You can even load up an 8 foot whip on 160 meters, but the
>radiation
>efficiency will be very low and your tuner will get very hot or
>arc.  I
>have an Alex loop that is 3 feet in diameter and it gets out
>surprisingly well even on 40 meters, but you can only use up to
>20 watts
>do to the close spacing in the tuning capacitor on the loop.
>
>Bob, K8LR, [log in to unmask]
>
>On 11/26/2014 4:24 PM, Tom Behler wrote:
>  Ron:
>
>  Thanks for the excellent concept review on SWR, reflected power,
>and antenna
>  tuners.
>
>  We all need reminders about this sort of thing from time to
>time.
>
>  In fact, I'm now thinking of making some modifications to my
>station, and am
>  trying to decide whether I can effectively do so with my current
>antenna
>  arrangement.  As you may recall, I use an Alpha Delta DXCC
>nulti-band dipole
>  on 40 through 10 meters, and a Cobra ultralite senior antenna,
>mainly for
>  the lower bands.
>
>  While these antennas have kept me on the air on the HF bands
>over the past
>  few years, I do wonder sometimes whether I might try something
>else to
>  improve my situation.  I do have limited space here, though,
>which makes the
>  issue of alternate wire antennas a bit challenging.  A tower and
>beam are
>  also out of the question at this time for financial and other
>more practical
>  reasons.
>
>
>  Anyway, your remarks are quite timely here, so thanks for
>sharing them.
>
>  Tom Behler: KB8TYJ
>
>
>  -----Original Message-----
>  From: For blind ham radio operators
>[mailto:[log in to unmask]]
>  On Behalf Of Dr.  Ronald E.  Milliman]\\`
>  Sent: Wednesday, November 26, 2014 4:07 PM
>  To: [log in to unmask]
>  Subject: SWR, antenna tuners, and reflected power
>
>  I am sure most of you know all about SWR (i.e.  Standing Wave
>Ratio), antenna
>  tuners, and reflected power.  However, it might be worth our
>discussing it
>  anyway for the benefit of those who might not be as familiar
>with these
>  relationships as others.  Many of us use antenna tuners, both
>manual and
>  automatic, for obtaining the best possible impedance match at
>the output
>  point of our transceivers with the objective of getting the SWR
>as close to
>  1.0 to 1 as we can.  A perfect match for most rigs is when the
>transceiver
>  sees a 50 ohm load at its output.  Anything above a 1:1 SWR
>represents some
>  level of mismatch.  Most of our transceivers can tolerate some
>mismatch
>  before it begins to reduce the power output as a means of
>protecting the
>  circuitry of the transceiver, and if the SWR or mismatch gets
>high enough,
>  it will cause the transceiver to reduce its power output to
>zero.  Many of us
>  have transceivers, like the Kenwood TS-590 and similar rigs,
>that have
>  built-in automatic antenna tuners.  These tuners work extremely
>well for
>  matching the impedance presented to the transceiver at its
>output, providing
>  this mismatch isn't too high.  How much is too high varies to
>some extent
>  from one make and model of transceiver to another.  If the
>mismatch is so
>  large that the rigs internal automatic tuner cannot bring the
>SWR down
>  within an acceptable level, you are faced with either adjusting
>your antenna
>  to achieve a better match at the point where the feedline
>connects to the
>  antenna, or you will need to obtain an external tuner to do the
>job.
>  External tuners, whether manual or automatic, tend to have much
>wider ranges
>  for matching the impedance of the feedline to the 50 ohms the
>transceiver
>  wants to see at its output.  A match at the transceiver's output
>does not
>  mean there is a match at the point where the feedline actually
>connects to
>  the antenna.  Even if the impedance at the output of the
>transceiver is
>  matched perfectly with an antenna tuner, there can be a very
>substantial
>  mismatch at the other end of the feedline where it connects to
>the antenna.
>  The larger this latter mismatch, the less actual power will be
>radiated by
>  the antenna and the more power from the transceiver will be
>reflected back
>  or remain in the feedline.  What happens to the reflected power
>depends
>  largely on the type of feedline used.  The difference between
>the power
>  radiated by the antenna and the output power of the transceiver
>is the
>  reflected power and may be totally lost power, depending upon
>the loss
>  rating of the feedline.  If coax is used for the feedline, this
>reflected
>  power ends up dissipating as heat in the coax and is pretty much
>totally
>  lost power.  If this heat is more than the coax can handle, it
>can burn up
>  the coax.  In contrast, open wire feedline is considerably less
>"lossy", and
>  much of the reflected power ends up being radiated by the open
>wire feedline
>  as opposed to ending up being dissipated in heat.
>
>
>
>  I am building up to two very important points that, in my
>opinion, do not
>  received nearly as much attention as they should.  The first
>point is that
>  reflected power is not good for your transceiver, or if you are
>using a
>  linear amplifier, it is not good for your amp.  If you are using
>a tube-type
>  linear, it can handle or tolerate more reflected power than the
>solid-state
>  type amps, but regardless, reflected power is bad for your rig
>and it is bad
>  for your amp.  Here is    my second point: just because your
>antenna tuner is
>  able to get the SWR down to 1.0 to 1 or an acceptable level at
>the output of
>  your transceiver or amp, that does not mean the reflected power
>is zero or
>  reduced to an acceptable level.  Most rigs and amps today have
>built-in
>  protection circuits that detect high SWR and high reflected
>power, and they
>  will shut completely down if either the SWR or reflected power
>is too high.
>  For example, I have a Kenwood TS-590 driving an Ameritron
>ALS-600, and my
>  antenna is an 80 meter, full-wave loop.  I feed the loop antenna
>with 50 ohm
>  coax and use a 2.5 to 1 matching ballun at the feedpoint of the
>antenna.  The
>  loop works extremely well on all bands 80 through 10 meters,
>including the
>  WARP bands.  However, there is a sizable mismatch on some bands
>at the
>  feedpoint of the antenna.  Without an antenna tuner, this
>mismatch would
>  present such a high SWR at the output of the transceiver or
>amplifier that
>  the protection circuits would reduce the power to zero or, in
>the case of
>  the amp, it would kick it off.  The mismatch is so high that the
>internal
>  tuner of the TS-590 cannot handle it.  So, I use a LDG AT1000PRO
>II external,
>  automatic antenna tuner, which has a much wider matching range,
>and it can
>  handle the mismatch and the power of the ALS-600 just fine.
>However, even
>  though I am able to get my SWR down to 1.0 to 1 on some bands
>and 1.5 to 1
>  or better on the others, I cannot run the amp at full power
>because if I do,
>  the reflected power is so high, over 50 watts, that it causes my
>ALS-600 to
>  kick off.  Therefore, I am forced to reduce my output power down
>to the point
>  where the reflected power is low enough that it won't shut the
>amp down.
>  Consequently, instead of putting out 600 watts from the amp, I
>have to
>  reduce the power to where I am putting out only about 300 watts.
>This keeps
>  my reflected power level below 50 watts, which is the critical
>level for the
>  ALS-600 amp, keeping it from completely shutting down.
>
>
>
>  Many years ago, when I was a young, foolish teenager, I put up
>an antenna
>  that had such a high SWR that I could get RF burns from the
>Microphone of my
>  transmitter.  The transmitter was a Heathkit DX-40, which had a
>PI-output
>  circuit that would allow me to load-up about anything for an
>antenna, but
>  back in those days, there were no protection circuits to
>automatically shut
>  the rig down if the SWR or reflected power was excessive.  As a
>result, the
>  high SWR and reflected power from trying to load and extremely
>mismatched
>  antenna caused my tank coil to get so hot that it melted the
>plastic
>  insulators that separated the windings of the tank coil; this
>caused the
>  tank coil to short, which, in turn, created a chain reaction,
>ending up in
>  wiping out the entire power supply.  My point is to simply
>illustrate what
>  high SWR and reflected power could do to your transceiver or amp
>if it
>  weren't for the protection circuits that are built into the
>modern gear.
>  However, even with the protection circuits, it is important to
>strive to
>  achieve the best possible resonant frequency match with your
>antenna and
>  then, between the feedline and your antenna and again between
>the feedline
>  and the output of your equipment.
>
>
>
>  I've had three people write to me off list asking me questions
>that related
>  to this whole topic, and so, I thought I would simply write this
>up and post
>  it to the list.  I'm not trying to show-off what I know; rather,
>I might be
>  showing-off what I don't know because there is a lot more about
>this stuff
>  that I know very little about, and I am absolutely certain that
>many of you
>  know tons more about some of this stuff than I do.  I'm just
>trying to be
>  helpful to some of the people that might be new that do not
>understand some
>  of these things.
>
>
>
>
>
>
>
>
>
>
>
>  Dr.  Ronald E.  Milliman
>
>  Retired Professor of Marketing
>
>
>
>  President: Millitronics, Inc.  (millitronics.biz)
>
>  President: South Central Kentucky Council of the Blind
>(SCKCB.ORG)