Which instrument to use as a replacement for the ASG100/140 depends on what features of the ASG you need. The ASG100 offered the following functions: 1.  Multitone test signals 2.  Audio/Video delay signals 3.  CCITT O.33 4.  Four second voice ID 5.  Left and right channel test tones, with frequency and amplitude selections, analog outputs via XLR connectors If you are in need of any of the items 1 through 4 (to drive a VM700T for example) then there is no current replacement product. Typically, ASG’s are available on the used market for those who still need these features. However, if you are simply interested in the features listed in item 5 (tone generation with selectable amplitude and frequency) then either the SPG300 or SPG600 would be a suitable replacement.