All Vintage Fender Amps are Clean Amps:

Fender has a reputation for amp with great clean tones so many people do not know that Fender also built amps with some of the most quintessential vintage over-driven  tones.  The Tweed amps and some of the Brownface/Blonde series amps have great over-driven tones.  In fact vintage Marshall amps are offshoots of the Western Electric circuit found in the 5F6A Tweed Bassman and 5F8A Tweed Twin.

 

Amps need Effect's Loops:

I cannot enumerate the amount of times customer have asked if I can put a effects loop in one amp or another. The fact of the matter is they are only really effective (pun intended!) in amps with lots of pre-amp gain.  An effects loop is placed between the pre-amp and power amp so to not have the effects sound become distorted by pre-amp distortion. This especially useful with reverb, delays and other time based effects .

 

Many vintage designs do not have enough pre-amp distortion for an effects loop to be beneficial.  Vintage designs often rely on power tube overdrive so this negates the usefulness the effects loop because the loop would be placed before the power section which is the main overdrive generator in such amps.