Hi David, From fuzzy memory, I believe that the 454 had about 6 nuvistors includ= ing a few in the first vertical amp and the "A" was all transistor. 73 & Good morning, Marv WC6W -- "David C. Hallam" wrote: What is the difference between a TEK 454 and a 454A? David KC2JD _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ________________________________________________________________________ Try Juno Platinum for Free! Then, only $9.95/month! Unlimited Internet Access with 1GB of Email Storage. Visit http://www.juno.com/value to sign up today!