There are lower cost rectifiers available with part number KBPC5010. They are known to cause problems so beware of buying a part with no numbers on show. I can assure you that the KBPC5010 is not a good idea on any valuable bike.
Triumph Tiger Cub T20B Bantam Cub Super Cub Oil Tank C15? (may be new old stock)
Triumph Tiger Cub T20B Bantam Cub 54935300 Speedometer Bulb Holder & 6V Bulb '
TRIUMPH TIGER CUB T20 & BANTAM CUB T20B SPEEDO CABLE 'NEW' 1963-1968 4' 10"
Triumph Tiger Cub T20B Bantam Cub 47205 Lucas RM21 Stator 2 Wire 12 Volt '
Triumph Tiger Cub Footrest Rubber (All Triumph Pillion)
Triumph Tiger Cub Oil Pipe