During my re-watching of some of the early SG-1 seasons, I came across a classic episode, "The Fifth Race". During this episode, using purely Terran technology, O'Neil constructs what is discovered to be a 'Power Booster Device'. While O'Neil DID have the entire repository of Ancient knowledge at his disposal, his materials (excepting the staff weapon power source) were entirely Terran.
This device, draining the entire power source for a Staff Weapon, was able to open a wormhole to an Asgard planet by supplementing the existing power source for the Earth gate.
They learned how to recharge it in a later episode, "Point of View", but left the device in an alternate reality.
Obviously, this device wouldn't solve all their problems - it's a one-shot device which requires some amount of rework before it can be used a second time, and it's doubtful it would work on non-Earth gates (without the power generators it's designed to hook into).
But why didn't they build a few more of these - they can be made from spare parts, powered by the plentiful staff weapons, and would have provided the Tau'Ri with a method of calling the Asgard in case of a serious emergency (prior to them gaining a reliable method of doing so). It also could have potentially served to open the wormhole to Atlantis...so why did they drain the Earth ZPM instead of building and using one of these?
In-universe answers preferred, the storytelling reasons are fairly obvious.