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When your pellet grill gets to temp, it's just not producing much smoke. The pellets are burning more efficiently, in-order to produce higher BTU's, so they produce less smoke. Let the pellets in the hopper produce heat, and the Tube produce smoke. Best of both worlds!
An Oak Based pellet like BBQrs Delight actually produce pretty darn good smoke in the Tube Smoker. It may not be as strong as Hickory, but oak still has a good flavor.
I was very pleased with BBQ delight and B & B pellets. Good smoke flavor and low ash output. And for $12 a 20lb bag on B & B pellets it's a great deal. I like oak as a base wood much better than alder and I also think it's a good flavor wood too.
I have a PID on my traeger so it is very efficient and doesn't produce enough smoke for my tastes...hence the Amazn tube and 100% flavor wood like hickory, cherry or mesquite.