The 8CG7 and 8FQ7 tubes are an 8 volt version of the 6SN7 in a miniature 9 pin tube. The 8CG7 is supposed to have an internal sheild, while the 8FQ7 doesn't. The reality is that most 8CQ7 tubes do not have the shield as they are just 8FQ7 tubes. In fact most tubes that were produced later were combination labeled 8CG7/8FQ7. These tubes are an 8 volt verison of the 6CG7/6FQ7 tubes which are the guts of the venerable 6SN7 tube crammed into a 9 pin minature tube. If you want to play with 6SN7 tubes but don't want to pay for those expensive tubes, the 8CG7/8FQ7 tubes are a great way to do it.
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Bargain Bin Vacuum Tubes