[TenTec] IDing version of 525 Argosy w/o serial nbr?

[David Feldman]

Have a use 525 Argosy that doesn't have (maybe never had?) serial number on back panel (could it be inside instead)? Trying to figure out whether it would use the 223 NB (for SN < 825) or 223A (for SN > 825). Any other way to determine which version, perhaps based on type number of the internal PC board that hosts the NB connections (the 80784 RF/MIXER board; my 525 80784 board is labeled "REV B")?

73 Dave WB0GAZ wb0gaz at yahoo.com