"i have old linclon 250 idealarc ac/dc have airco hf pack on it. Would like to know if it would be worthwhile upgrading to new hf with pulse and square wave. I am a retired pipe welder and still like to do my hobby things."
If your unit is working ok, I dont know that you will realize great benefits from a newer square wave welder, especially if you weld infrequently and on hobby projects.
If you start doing a lot of aluminum that needs to be somewhat precise, Squarewave with A/C balance control makes a difference.
To take it one step further, A TIG inverter like a Miller dynasty 200dx gives you all kinds of options beyond squarewave ...as well as ability to pulse at 499 pulses per second. ( like love to pulse stainless at 150 pps).
That said, I have used some old welders like yours and was pretty much able get a good looking weld if I really wanted to. The pulsing and squarewave do make a difference , just not like night and day.
The biggest and cheapest difference would be to get a bottle of 50/50 argon/helium for welding aluminum with your current machine. This gives a lot of bang for the buck...you can probable get an owners size bottler (125 cubic feet) for around 200 bucks or maybe slightly less.
It makes a huge difference.