the specs say plus or minus 5 per cent...so yup, it's within spec.
The swr not being at flat 1 to 1 will throw it off a bit, usually by a 
couple watts either way.
and the radio's diagnostics will always be pretty generous.
I suspect the readings on the radio are programmed bassed upon settings 
rather than actual real world RF readings.
So if you set the rig to tx 57 watts, the meter on the rig will probably 
say, 57 watts.
but your outboard meter, measuring RF without any sort of  built in bias, 
will give you a more accurate reading.
presumably this is in cw mode your checking right?
Can you get 100W on the TW1 by setting mike gain all the way up, power all 
the way up and running the processer hot on SSB, and giving a whistle into 
the mike?

73
Colin, V A6BS
----- Original Message ----- 
From: "John Miller" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 30, 2011 4:18 PM
Subject: Re: Wonder if these TS590 output power readings sound reasonable?


> That's within spec for the tw-1. It may not be dead on but that is in the
> acceptable range.
> ----- Original Message ----- 
> From: "tom behler" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, June 30, 2011 6:08 PM
> Subject: Wonder if these TS590 output power readings sound reasonable?
>
>
>> Hi, all.
>>
>> Well, I have done some fairly extensive testing on the output power
>> readings
>> for my TS590, and I wonder if what I'm seeing is what can be reasonably
>> expected.
>>
>> Let me start with some general background:
>>
>> First of all, I took the voltage reading from my Astron RS35 linear power
>> supply, and it read about 13.8 volts--right where I had hoped it would 
>> be.
>>
>> Then, I took a bunch of SWR and output power readings, on various bands
>> and
>> frequencies, using my DXCC and Windom antennas.
>>
>> My best readings were found on 80 meters, where I could get my Alpha 
>> Delta
>> DXCC antenna down to an SWR of 1.2 to 1.  I can get reasonably low SWR's
>> on
>> other bands and frequencies with the DXCC or my Windom, but without an
>> antenna analyzer, the 80-meter frequency with the DXCC was the lowest I
>> could get.  All readings were taken with the internal automatic antenna
>> tuner off.
>>
>> With a 1.2 to 1 SWR reading on 80 meters, my LDG Tw1 gave me a forward
>> power
>> reading of 95 watts, and a reflected power reading of 1.2 watts.
>>
>> Just for kicks, I had my sighted XYL look at the watt meter on the TS590,
>> and she said it was pegged at the maximum 100 watt level.  My XYL also
>> approximated my output power using the meter on my Tentech 238A manual
>> tuner, and she said it looked to be just a hair below 100 watts.
>>
>> Interestingly, for reasons which I can't quite figure out, my output 
>> power
>> reading was slightly lower when I used a dry dummy load.  Specifically,
>> the
>> readings ranged from 90 to 93 watts with the dummy load connected after
>> the
>> TW1.
>>
>> Do these readings seem reasonable?
>>
>> Actually, I'm wondering if my TW1 is slightly off callibration.
>>
>> If so, does anyone know how or whether the TW1 can be callibrated?
>>
>> I'd be interested in any thoughts anyone has.
>>
>> 73 from Tom Behler:  KB8TYJ