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My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

Dave WB3DWE Temple, TX

The numbers you have are the input to the final tubes. The rig will put out
around 100 to 120 watts CW.

Dummy loads are usually rated for so much power for so long of a time. Some
will be good for 100 watts continious and maybe 300 or 500 for a short time
such as 30 seconds , with a cooling off period of 5 minuits.

I have a comercial one that is built with a pl259 on the end. The dummy
load is about 3 inches long and 2 inches in diameter. It is rated for 15
watts continious and 100 watts for 15 seconds with a cooling off period of
so long. I have ran a 100 watt rig into it for a short period of time. It
does get very hot after a few seconds. The old Heathkit dummy I have is a
resistor in a gallon 'paint can'. It is full of oil and can take a KW for a
short period of time.

I picked up some dummy loads at a hamfest that are good for about 50 watts
and not sure how long or how much power they will take. I did hit they
with around 100 watts for about 30 seconds to check out a rig and they took
it,but they did get very warm.

For the ts520 you can use a 100 watt light bulb. I would not recommend it
for any rig with transistors for the output, but it is fine for the tube
rigs. Just use about a foot of coax to the light bulb. They will radiate
a small ammount of power, but not enough to both most stations.
You just tune for maximum brightness. If you have a wattmeter, it will
probably not be accurate into the light bulb as it is not 50 ohms, but good
enough to tune the rig to see if the power out is around 100 watts.