Fulltone tube tape echo Owner's Manual page 2

Basic History of major TTE Revisions
Serial# 2326 6/2008: Discontinue 12AT7 for V3 Erase tube. Change to Fulltone
12AU7. Warning! You must use either Shugwang 12AU7 or Fulltone 12AU7. Most
tubes will not erase properly, no matter how much you'd like to use that vintage NOS
tube you bought for way too much money ;)
Serial# 3179 4/2011: Discontinue padded gig bag, first TTE with removable, hinged
Lid. Majority of production uses Blonde Tolex.
Serial# 3460 5/2012: Changed Preamp circuit, revised EQ of preamp to be more
Full-range, with less change to the original instrument tone. Previous versions were
much brighter, lacking in bass frequencies.
Serial# 3480 10/2012: First production TTE with "Relay-Activated Echo Cancel."
This is a major improvement in that using an Echo Cancel Footswitch no longer has
a negative effect on the sound quality and volume of the Echoes! From this point on,
you are not limited to using a short cable for an Echo Footswitch, and instead can
use up to 500' of any 2 conductor, standard instrument cable. Fulltone unveils our
Echo Cancel Footswitch (ECF) which requires no external power for its status LED's
(more info or purchase here)
Serial# 3664 6/2013: TTE goes to all black metal and black Tolex cabinet & lid.
Major improvement to tape transport initiated by changing the spacing on the tape
guide posts, eliminating much of the friction and reducing tape jam.