Hi Jeff,
New 6U5 tubes are still available but are a bit pricey. If you look here on NA under References you will find a article on "eye" tubes. There are substition tubes using a adaptor. The main one is the 1629 tube but requires the adaptor mentioned earlier.
You can use a 6E5 or 6G5 without an adaptor but again they are more costly than a 1629.
Take care
Bud
:The tuning Eye on my Silvertone Model 6438B does not light up. Can I Still get the 6U5 tube that is listed as the Tuning Tube. Also - I noticed some other posts that say other tubes will work. Thanks