Dating hiwatt amps
Check all the bolts securing that speaker and make sure they're snug.
Though, when Geocities went down, I lost all the drafts of other pages I had in the works. I dont have pic yet as it is in the shop for service but will soon. The 1973 Orange amps have the serial number stamped into the chassis and the serial number will start in the 10000 range along with the pix and text faceplate. I wonder what that mod is on the front of the faceplate? First of all you got yourself the best clean cranking amp ever!
Various Mark 3 and Mark 4 PA heads also appeared, as did a few Mark 4-era "slave" heads.
It's easiest to determine the range of years of manufacture by the models themselves and by specific cosmeticdifferences between them (changes in grill cloth, piping and vein, trim, handles, corners, wheels, etc.). Seriously, the best way to determine value is by watching how much amps and cabs fetch on e Bay.
There really is no hard and fast method of appraising Sound City equipment; they've spent far too much time as poor stepchildren to Hiwatts for anyone to take them seriously as collectibles, but they are collectible in their own way.
To a great extent, condition, originality, and, especially, model determine price.
Search for dating hiwatt amps:
This is a tough one, and short of various inspection stickers, and reliable transformer codes and pot codes, there is currently no definitively reliable way to determine an accurate date based on serial numbers alone, with the possible exceptions of the DMI-era products and beyond.