Thanks Tom and all who contributed, I appreciate the time spent.
73,
Rob WA9UAA

Hi All,
In checking the power through then tuner I made the adjustments as the setting for one end of the band was not the same as the other.  With the THP meter I am simply reading forward power. Here are the readings with the tuner in the bypass position.

Frequency     3550 KHz                               3950 KHz
THP meter     580 W...................................590 W
Mobile meter 610 W....................................610W
Tuner meter  600 W....................................590W

The Palstar meters are cross needle type, in each case with the above readings (today) the reflected power was ~~ 1/2 watt.
73,
Rob

Here you go, all readings through the tuner into the DL with the tuner tuned to 1:1 SWR

Frequency                3550 KHz                    3950 KHz
THP Meter                 600W........................600W
Palstar Mobile meter  650W........................675W
Palstar Tuner meter   600W........................550W

Thanks and 73,
Rob WA9UAA

Thanks for the updates, I understand that the band aid fixes don't get rid of the problem. Would substituting another power meter/ tuner-metering-system lead to some sort of verification of whether or not the amplifier is faulty, depending upon how it behaves? 
73,
Rob WA9UAA

Good Day,
The only way I can verify, seriously, is to compare the other meter readings. I have an older Palstar mobile watt meter with a 2KW full scale. It agrees with the THP meter on the amplifier easily +/- 10 % I'd say. I got into a qso on 75 meters a couple of days ago, mentioned the problem and while I also got a bunch of suggestions as to enhancing the audio one fellow looked at the signal on his scope, saw a trapezoid pattern and said it was clean. If I have a spur somewhere else that not going to be detectable. I wouldn't be surprised to find one in any case. The question would be what does it measure in dBc.

I've got a lightning ground outside the shack that is connected to the house ground at the meter. There are 4 ground rods between the ends of the ground system with the lightning ground at one end. What bothers me about grounding the station is that any large strike dumped into the ground is going to light up the equipment to the same potential abet for a short time. The house ground being 30 some feet away may be enough delay to still develop some nasty potential difference in the shack. BTW, The amp is wired split 220 so it's chassis is grounded via the neutral. (I hope) So, are my grounding concerns valid? What else can I do to verify that the amp is clean. Again, thanks to all for the concern, help and suggestions.
73,
Rob WA9UAA 

W5WSS,
Thanks for your reply, the THP protection is not tripping in this case. The output now appears to be consistent with the mobile Palstar meter. BTW, the tuner is a recent purchase, I have had all the other gear for several years. The initial issue was what appeared to be a 150 watt difference in output of the amp at either end of the 80M band when the amp was presented with a 50 ohm resistive match in both cases. I was initially relying on the Palstar tuner meter as everything else I have had from them has been first rate at least to my level of expertise. The THP meter now appears to be consistent as does the older Palstar meter.

The CM current on the interior of the coax shield is a new one on me, I have always seen it illustrated on the outside of the shield . W8JI and W5DXP had an intense discussion on this current flow in an unbalanced antenna system a few years ago.
73,
Rob WA9UAA

No actual schematic of the Palstar coupler in the manual. The THP unit uses transformer coupling, toroidal transformers mounted around the trace on the pcb, diodes to generate DC voltages and a RFC and frequency compensating parts (I think). This appears to be true directional coupling.

The metering in the Palstar on the Low range seems linear from one end of the band to the other as does the THP metering where the full scale 1 kW. Full scale on the Palstar high range is 3KW. Hmmm A man with one watch knows the time, a man with two watches is never sure unless they are linked to the NIST.

I just put the Palstar mobile watt meter in line between the amp and tuner, it reads 600 watts out at the high end of the band where the circuit in the tuner still shows 450 watts. This meter is 2KW full scale.
73,
Rob WA9UAA

I certainly prefer this compared to getting the amp fixed!

Hi All, have been back and forth with the second rig and the output is still low on the Palstar meter at 3950 Khz. Taking Dave's copy of what I had done before to heart, with the rig at 3943 Khz I took a quick look at the THP meter reading, 600 watts on the money at 3943 Khz, at the same time the Palstar meter said 450 watts. The THP meter at 3547Khz shows with in a needle's width of 600 watts key down, if I were to guess it would be 590 watts. The Palstar meter seems to be low at the higher frequency. The rig itself tops out at between 80-85 watts so I can't drive the amp any harder which is probably a good thing.

I took the risk of getting in with group on 75M this morning, all thought the audio was fine and offered suggestions to tweak it. One fellow looked at the signal on his scope and saw a good trapezoid pattern.  My fault for trusting one meter over another though skeptically how do I know it's "right" when the other isn't?  Thanks again to all, while I don't have the money for a spectrum analyzer Does anybody know of a more linear reading output meter and more to the point is there another way of monitoring my signal? (Good scope recommendation?) They say when a THP amp fails somebody has to go out and commit Seppuku.  I hope I just saved a worker at THP. Again thanks to everybody the weighed in on this.
73,
Rob WA9UAA

My balun connection, "I am running a THP 1.2 Kfx The amplifier is fine into a dummy load. Here is the issue, I run tuned feeders, 18 ga ladder line ~~ 137 ft., via a Palstar AT2K and a DX Engineering 1:1 balun on the output. The balun is connected to the tuner by about 6" of RG-8 size cable."
73,
Rob WA9UAA


HA! page 2

Hi Tom,
My reference to resonance is to say that the Amp is seeing a resistive load. I have been using a MFJ 259B, it seems to agree with the tuner on 1:1 match points. The line between the tuner and amplifier is a W2DU balun with my intent of keeping any R.F. on the outside of the tuner away from the amp. I don't have the tuner grounded to the system outside as I can't get past the idea of the chassis' on my gear lighting up to what ever charge might show up on the ground system. The ground is connected back to the house ground through a system of ground rods so it may be OK.

Quote W8JI,"I don't know why you are worrying about resonance, or how you are measuring it. You have an antenna tuner and ladder line. An antenna tuner with ladder line makes resonance, however you are measuring it, a moot point."  end quote

I had been operating under the perhaps mistaken notion that having the antenna at resonance some how made it easier for the tuner to pass the full power from the amplifier to the antenna as this seemed to reflect (pun intended) what I was seeing happen. Though for what now seem to be the wrong reasons.

I'd hope it is not the Amp, I probably do have some imbalance in the antenna system as I have a tree branch near one side the 80M dipole. Having just redone the antenna system, I did not have any tree branches near the antenna before.

I'd need to be reassured about grounding the station to the same place as the lightning ground and as you say it won't fix a balance problem related to the tree branch or not. I just have to get to the tree branch.
I have not heard any RF in my audio but have no idea where the rig gets it's sample of audio for monitoring.

Considering RF in the shack as a source of the problem, the ladder line does not make a 'clean' path away from the balun. It's too close to the chassis. Conservatively speaking, running this antenna from 80m to 6M, how long can the coax between the tuner and the balun be, if the coax is well assembled, and not impact the performance?

Looking at your other points, I can put another SWR meter between the rig and amplifier to see if the rig or supply is folding back.

Thanks again Tom I have several things to look at, the length of coax between the balun and tuner is something I'll really need advice on. Is there any reason to believe that the longer the coax between the tuner and balun seems to decrease the amount of real 'R' seen by the tuner?
Time to back out of here before I become more incoherent.
73
Rob WA9UAA

Hi Tom and all,
Thanks for weighing in here. Yes there is a tuner in line between the amp and feed line. The length of ladder line to the antenna is 140 - 137 ft. No meters on the window line. There are two issues here, one is the power level (TPO) changing even though the the amplifier is tuned to a 1:1 match.  The other is the fact that I seem to be having to trim large amounts of wire to achieve resonance where I want it frequency wise. The dipole was cut by the book for the middle of the band and showed resonance about 140 Khz below the band. After cutting 4 feet off each  end of the dipole and using a foot of wire for the wrap on each end I found resonance at ~~3540 Khz or so. It's raining here and resonance is again below the band edge.    I started checking the antenna and tuner using my MFJ 259B and have been setting the tuner up to pretty much 50 Ohms (J0) with as much capacitance as possible. I have seen the low power thing in the paging industry on PAs and later saw the PA was in oscillation, not often, but it happened. One thing I can try is to see if I can find a better match on the high end of 75M with more capacitance on the output of the tuner.   I just had an A-HA moment, I left out what may be an important detail. Having a ladder line fed antenna, it is switched to ground outside the shack with a large DPDT knife switch. In my interest in draining charges from the antenna system I installed a pair of Dale HL-50D6z 100 K Ohm 50 watt wire wound resistors from the high side of the ground switch to ground through about 5 feet of inch wide strap to the ground system.   I seem to remember a little extra capacitance adds to the stability of any system. I going to stop here and wait for feed back on the power resistors, they are always connected between the feed line and ground.
73,
Rob WA9UAA

p.s. Hi Fred Yes, it is a THP 1.2 Kfx. I am actually trying to make the antenna resonant mid band on 75-80 meters. There is a 40M dipole connected in parallel with the 80m antenna though I don't seem to have as much if any problem on 40 meters. The 1:1 current balun is correct in this instance as the antenna should show 50 Ohms on 80M. I am suspecting the 100K Ohm Wire wound resistors that are acting as current drains. (see above)

ETA. I just took the resistors out of the circuit and did a quick tune up on each end of the band. On the low end of the band ~~3550 I show a bit over 550 Watts at max drive. At the high end of the band above 3950 I see a bit over 400 watts out.  

ETA 2 Tuning into the dummy load at the low end of the band I get 600W out and 550W at the high end of the band.  I guess the resistors can go back in later though I'll wait until the line drys out tomorrow.

Hi Fred,
Yes I am running window line. The antennas are 80M and 40M dipoles that show in band resonance via the 1:1 balun though the 80 meter resonant point could be a little higher. It's resonant at 3.540 or so. I decided to go with resonance on these two antennas and let the chips fall where they may on the higher frequencies. One antenna question I have is whether or not I could trim the ladder line to bring the 80M antenna closer to the center of the band? I took 5 feet off each side and that brought it up 140 Khz. Cut by the book it should have been resonant at 3750. All this to provide a more reasonable match for the tuner. The amplifier question is why do I get 600W output at the low end of the band and only (sic) 480W at 3950 where the tuner shows a 1:1 match and the uncorrected VSWR is ~~ 8:1?
73,
Rob WA9UAA

Hi Stan,
Same here, I didn't know about the need for a ground plane. The appeal for me was the "easy" setup. One pipe driven into the ground and some coax. hihi
73,
Rob WA9UAA

Additional info.
All readings through the tuner matched to 1:1

Rig at 3550 Khz................................................................3950 Khz
Output to DL 83W maximum.............................................82W to Ant.
Antenna  82W to DL..........................................................80W to Ant.
Amplifier 600W to DL.......................................................480W to Ant.

Amplifier
Meter      580W to DL........................................................590W to Ant.

Metering issues ? I have seen this on another tuner but with a different antenna.