[mikethedruid]

The G just refers to the outer form of the tube. A G tube has a glass envelope, tubes without the G are usually the metal outside kind. These will usually work fine. Problems can come from the wires going to grid caps, because the metal tubes are often shorter in height than the G suffix tubes. This can cause the wire to not reach the grid cap if the tube shield is left in place. Metal tubes do not really need the tube shield, so if this is a problem, just put it aside and save it for when you can get a G tube. The metal tube should be OK for testing and use, but SAVE THE SHIELD. One can have a similar, or worse problem using GT tubes which ARE glass envelope, and need a shield, but are smaller in form factor than the G tube... in that case one lengthens, or replaces with a longer wire, the grid cap wire. This trick can also work so you can use the shield around metal tubes, but be careful routing the wire, lengthening it can make it more susceptable to feedback and such.