Hello Dave, your 300 might have one of the more basic pulsers when compared to some that are available on other machines. It may give you PPS (pulses per second) and the ability to select a percentage of your peak amperage to determine your background amperage. Peak would be referring to the high amperage value in the pulse mode and background would be referring to the low amperage value. Essentially, in a simple form, pulsing is switching the amperage from a high value to a low value at different rates and possibly lengths of time to allow for a higher average amperage. This allows for a higher welding speed while still allowing for control of the puddle in out-of-position welds. It can also allow for the "surface tension breaking action" that 357 was referring to on the thin-gauge stainless and I believe it will also aid with "cleaning action" sometimes when welding on aluminum or magnesium. If your machine has a AC balance control this will allow you to select a balance of the DCEN vs. DCEP to aid with penetration or cleaning by allowing a longer dwell time on DCEP to aid with cleaning or a longer dwell time on DCEN to help with penetration while welding on aluminum or magnesium.
On many of the modern pulsing power sources(mainly referring to inverters), the parameters of control for pulsing can take on many different aspects of arc control. With DC Pulse: different amperage values for peak and background, different dwell times for peak compared to background, different frequencies, different pulse waveforms. AC Pulse can be even more complex and complicated as recent technological advances have incorporated many of the same basic control items as DC and have also included: variable hertz DCEP to DCEN switching times other than the traditional 60 hertz that used to be the rule, squarewave and other waveforms of EP/EN current transition, AC balance control of varying types, in some cases an imposition of DCEN in conjunction with the AC current. I'm sure there are other forms of technology that I haven't touched on. Hope this helps explain it a bit. Best regards, Allan
One additional thought to add: you've possibly noticed when you go to tack up with the GTAW process that if you ramp the heat up too slowly it will cause the two edges of the joint to melt and ball away from one another. On the other hand, if you are somewhat aggressive, initially, when you apply the amperage and then back-off, the tack will bridge much easier and allow for fusion between the two pieces. In a similar fashion the "pulsing" action, when pulse is engaged on a machine, can help with easier weld progression. An analogy that I believe illustrates a benefit of pulsing in some cases.
To set up pulsing gtaw. First, set the pulsing controls. Second, have a pen/pencil & paper; write it down! Third, weld and see what changes are made. Fourth, change one and only variable at a time. Fifth, do not change more than one variable at a time.
First alternating current, set the balance control at max penetration, imho it is a waste of this control to have anything but maximum time at negative polarity. The 300 has I believe 68% time at negative. Sharpen the ceriated tungsten to a point.
Use the formula - 1 amp of current for 0.001" thickness. Welding 1/8" (10 gauge) aluminum would call for 125 amperes. Multiply this amperage by 1 1 / 2 (1.5) = 187.5 or thereabouts - set 190 amps on the main amperage control. This is the peak amperage.
Multiply the 125 amps (nonpulsing) by 1 /4 (25%) = 31.25 or thereabouts - set 30 amps. This is the background amperage.
Set the Per Cent (%) on time control at 60%. This is peak amperage on time.
Set the Pulse frequency (Peak Amperage Pulses-Per-Second) to one or two peak amperage pulses per second.
The remote control device will limit all variables if it is not set at maximum; ie. foot control device/pedal all the way down.
If the tungsten melts excessively or balls/does not hold a point; increase the diameter of tungsten; change from the 3/32" to 1/8" diameter. (one variable change).
Determine the overlapping fusion weld nuggets. Increase/decrease the pulse frequency until the desired weld pool ripple is achieved.
Allen & 357: Thanks, I understood the basics and played with the pulse settings a bit when I first set the machine up just to verify that it worked, but this thread was the first I heard of using the pulse to break the surface tension. My machine has 1 to 10 on the wave balance, it may be 68% at max penetration. I know these machines don't go as far in that direction as the inverters do. My old machine [Airco version of a 360 A B/P] has a seperate pulser box, I never messed with it, and the previous owners didn't either. Once again, thanks for the specifics.
One can also pulse sort of - with a remote amperage foot pedal control if one doesn't have a built in pulsing attachment on their power source, or a separate attached unit... 
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